/*
 * Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javafx.scene.control;

import com.sun.javafx.collections.MappingChange;
import com.sun.javafx.collections.NonIterableChange;
import com.sun.javafx.scene.control.Properties;
import com.sun.javafx.scene.control.SelectedCellsMap;

import com.sun.javafx.scene.control.behavior.TableCellBehavior;
import com.sun.javafx.scene.control.behavior.TableCellBehaviorBase;
import com.sun.javafx.scene.control.behavior.TreeTableCellBehavior;
import javafx.beans.property.DoubleProperty;
import javafx.css.CssMetaData;
import javafx.css.PseudoClass;

import javafx.css.converter.SizeConverter;
import com.sun.javafx.scene.control.ReadOnlyUnbackedObservableList;
import com.sun.javafx.scene.control.TableColumnComparatorBase;

import javafx.css.Styleable;
import javafx.css.StyleableDoubleProperty;
import javafx.css.StyleableProperty;
import javafx.event.WeakEventHandler;

import javafx.scene.control.skin.TreeTableViewSkin;

import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

import javafx.application.Platform;
import javafx.beans.DefaultProperty;
import javafx.beans.InvalidationListener;
import javafx.beans.WeakInvalidationListener;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.ObjectPropertyBase;
import javafx.beans.property.ReadOnlyIntegerProperty;
import javafx.beans.property.ReadOnlyIntegerWrapper;
import javafx.beans.property.ReadOnlyObjectProperty;
import javafx.beans.property.ReadOnlyObjectWrapper;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.WeakChangeListener;
import javafx.beans.value.WritableValue;
import javafx.collections.FXCollections;
import javafx.collections.ListChangeListener;
import javafx.collections.MapChangeListener;
import javafx.collections.ObservableList;
import javafx.collections.WeakListChangeListener;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.event.EventType;
import javafx.scene.AccessibleAttribute;
import javafx.scene.AccessibleRole;
import javafx.scene.Node;
import javafx.scene.layout.Region;
import javafx.util.Callback;

The TreeTableView control is designed to visualize an unlimited number of rows of data, broken out into columns. The TreeTableView control is conceptually very similar to the TreeView and TableView controls, and as you read on you'll come to see the APIs are largely the same. However, to give a high-level overview, you'll note that the TreeTableView uses the same TreeItem API as TreeView, and that you therefore are required to simply set the root node in the TreeTableView. Similarly, the TreeTableView control makes use of the same TableColumn-based approach that the TableView control uses, except instead of using the TableView-specific TableColumn class, you should instead use the TreeTableView-specific TreeTableColumn class instead. For an example on how to create a TreeTableView instance, refer to the 'Creating a TreeTableView' control section below. 
As with the TableView control, the TreeTableView control has a number of features, including: 

Powerful TreeTableColumn API: 

  
Support for cell factories to easily customize cell contents in both rendering and editing states. 
Specification of minWidth/ prefWidth/ maxWidth, and also fixed width columns. 
Width resizing by the user at runtime.
  
Column reordering by the user at runtime.
  
Built-in support for column nesting 
Different resizing policies to dictate what happens when the user resizes columns. 
Support for multiple column sorting by clicking the column header (hold down Shift keyboard key whilst clicking on a header to sort by multiple columns). 
Creating a TreeTableView
Creating a TreeTableView is a multi-step process, and also depends on the
underlying data model needing to be represented. For this example we'll use
the TreeTableView to visualise a file system, and will therefore make use
of an imaginary (and vastly simplified) File class as defined below:

public class File {
    private StringProperty name;
    public void setName(String value) { nameProperty().set(value); }
    public String getName() { return nameProperty().get(); }
    public StringProperty nameProperty() {
        if (name == null) name = new SimpleStringProperty(this, "name");
        return name;
    }
    private LongProperty lastModified;
    public void setLastModified(long value) { lastModifiedProperty().set(value); }
    public long getLastModified() { return lastModifiedProperty().get(); }
    public LongProperty lastModifiedProperty() {
        if (lastModified == null) lastModified = new SimpleLongProperty(this, "lastModified");
        return lastModified;
    }
 }
Firstly, a TreeTableView instance needs to be defined, as such:

TreeTableView<File> treeTable = new TreeTableView<>();
With the basic TreeTableView instantiated, we next focus on the data model.
As mentioned, for this example, we'll be representing a file system using File
instances. To do this, we need to define the root node of the tree table, as such:

TreeItem<File> root = new TreeItem<>(new File("/"));
treeTable.setRoot(root);
With the root set as such, the TreeTableView will automatically update whenever the children of the root changes. 
At this point we now have a TreeTableView hooked up to observe the root TreeItem instance. The missing ingredient now is the means of splitting out the data contained within the model and representing it in one or more TreeTableColumn instances. To create a two-column TreeTableView to show the file name and last modified properties, we extend the code shown above as follows: 

TreeTableColumns<File,String> fileNameCol = new TreeTableColumn<>("Filename");
TreeTableColumns<File,Long> lastModifiedCol = new TreeTableColumn<>("Size");
table.getColumns().setAll(fileNameCol, lastModifiedCol);
With the code shown above we have nearly fully defined the minimum properties required to create a TreeTableView instance. The only thing missing is the cell value factories for the two columns - it is these that are responsible for determining the value of a cell in a given row. Commonly these can be specified using the TreeItemPropertyValueFactory class, but failing that you can also create an anonymous inner class and do whatever is necessary. For example, using TreeItemPropertyValueFactory you would do the following: 

fileNameCol.setCellValueFactory(new TreeItemPropertyValueFactory("name"));
lastModifiedCol.setCellValueFactory(new TreeItemPropertyValueFactory("lastModified"));
Running this code (assuming the file system structure is probably built up in
memory) will result in a TreeTableView being shown with two columns for name
and lastModified. Any other properties of the File class will not be shown, as
no TreeTableColumns are defined for them.
TreeTableView support for classes that don't contain properties
The code shown above is the shortest possible code for creating a TreeTableView when the domain objects are designed with JavaFX properties in mind (additionally, TreeItemPropertyValueFactory supports normal JavaBean properties too, although there is a caveat to this, so refer to the class documentation for more information). When this is not the case, it is necessary to provide a custom cell value factory. More information about cell value factories can be found in the TreeTableColumn API documentation, but briefly, here is how a TreeTableColumns could be specified: 

firstNameCol.setCellValueFactory(new Callback<CellDataFeatures<Person, String>, ObservableValue<String>>() {
    public ObservableValue<String> call(CellDataFeatures<Person, String> p) {
        // p.getValue() returns the TreeItem<Person> instance for a particular TreeTableView row,
        // p.getValue().getValue() returns the Person instance inside the TreeItem<Person>
        return p.getValue().getValue().firstNameProperty();
    }
 });
}
TreeTableView Selection / Focus APIs
To track selection and focus, it is necessary to become familiar with the SelectionModel and FocusModel classes. A TreeTableView has at most one instance of each of these classes, available from selectionModel and focusModel properties, respectively. Whilst it is possible to use this API to set a new selection model, in most circumstances this is not necessary - the default selection and focus models should work in most circumstances. 
The default SelectionModel used when instantiating a TreeTableView is an implementation of the MultipleSelectionModel abstract class. However, as noted in the API documentation for the selectionMode property, the default value is SelectionMode.SINGLE. To enable multiple selection in a default TreeTableView instance, it is therefore necessary to do the following: 

treeTableView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
Customizing TreeTableView Visuals
The visuals of the TreeTableView can be entirely customized by replacing the default row factory. A row factory is used to generate TreeTableRow instances, which are used to represent an entire row in the TreeTableView. 
In many cases, this is not what is desired however, as it is more commonly the case that cells be customized on a per-column basis, not a per-row basis. It is therefore important to note that a TreeTableRow is not a TreeTableCell. A TreeTableRow is simply a container for zero or more TreeTableCell, and in most circumstances it is more likely that you'll want to create custom TreeTableCells, rather than TreeTableRows. The primary use case for creating custom TreeTableRow instances would most probably be to introduce some form of column spanning support. 
You can create custom TreeTableCell instances per column by assigning the appropriate function to the TreeTableColumns cell factory property. 
See the Cell class documentation for a more complete description of how to write custom Cells. 
Editing
This control supports inline editing of values, and this section attempts to
give an overview of the available APIs and how you should use them.
Firstly, cell editing most commonly requires a different user interface than when a cell is not being edited. This is the responsibility of the Cell implementation being used. For TreeTableView, it is highly recommended that editing be per-TreeTableColumn, rather than per row, as more often than not you want users to edit each column value differently, and this approach allows for editors specific to each column. It is your choice whether the cell is permanently in an editing state (e.g. this is common for CheckBox cells), or to switch to a different UI when editing begins (e.g. when a double-click is received on a cell).
To know when editing has been requested on a cell, simply override the Cell.startEdit() method, and update the cell text and graphic properties as appropriate (e.g. set the text to null and set the graphic to be a TextField). Additionally, you should also override Cell.cancelEdit() to reset the UI back to its original visual state when the editing concludes. In both cases it is important that you also ensure that you call the super method to have the cell perform all duties it must do to enter or exit its editing mode.
Once your cell is in an editing state, the next thing you are most probably interested in is how to commit or cancel the editing that is taking place. This is your responsibility as the cell factory provider. Your cell implementation will know when the editing is over, based on the user input (e.g. when the user presses the Enter or ESC keys on their keyboard). When this happens, it is your responsibility to call Cell.commitEdit(Object) or Cell.cancelEdit(), as appropriate.
When you call Cell.commitEdit(Object) an event is fired to the TreeTableView, which you can observe by adding an EventHandler via TreeTableColumn.setOnEditCommit(EventHandler). Similarly, you can also observe edit events for edit start and edit cancel.
By default the TreeTableColumn edit commit handler is non-null, with a default handler that attempts to overwrite the property value for the item in the currently-being-edited row. It is able to do this as the Cell.commitEdit(Object) method is passed in the new value, and this is passed along to the edit commit handler via the CellEditEvent that is fired. It is simply a matter of calling CellEditEvent.getNewValue() to retrieve this value. 
It is very important to note that if you call TreeTableColumn.setOnEditCommit(EventHandler) with your own EventHandler, then you will be removing the default handler. Unless you then handle the writeback to the property (or the relevant data source), nothing will happen. You can work around this by using the TableColumnBase.addEventHandler(EventType, EventHandler) method to add a TreeTableColumn.EDIT_COMMIT_EVENT EventType with your desired EventHandler as the second argument. Using this method, you will not replace the default implementation, but you will be notified when an edit commit has occurred.
Hopefully this summary answers some of the commonly asked questions.
Fortunately, JavaFX ships with a number of pre-built cell factories that
handle all the editing requirements on your behalf. You can find these
pre-built cell factories in the javafx.scene.control.cell package.
Type parameters:
<S> – The type of the TreeItem instances used in this TreeTableView.
See Also:
TreeTableColumn
TreeTablePosition
Since:
JavaFX 8.0/**
 * The TreeTableView control is designed to visualize an unlimited number of rows
 * of data, broken out into columns. The TreeTableView control is conceptually
 * very similar to the {@link TreeView} and {@link TableView} controls,
 * and as you read on you'll come to see the APIs are largely the same.
 * However, to give a high-level overview, you'll note that the TreeTableView
 * uses the same {@link TreeItem} API as {@link TreeView},
 * and that you therefore are required to simply set the
 * {@link #rootProperty() root node} in the TreeTableView. Similarly, the
 * TreeTableView control makes use of the same TableColumn-based approach that
 * the {@link TableView} control uses, except instead of using the
 * TableView-specific {@link TableColumn} class, you should instead use the
 * TreeTableView-specific {@link TreeTableColumn} class instead. For an
 * example on how to create a TreeTableView instance, refer to the 'Creating a
 * TreeTableView' control section below.
 *
 * <p>As with the {@link TableView} control, the TreeTableView control has a
 * number of features, including:
 * <ul>
 * <li>Powerful {@link TreeTableColumn} API:
 *   <ul>
 *   <li>Support for {@link TreeTableColumn#cellFactoryProperty() cell factories} to
 *      easily customize {@link Cell cell} contents in both rendering and editing
 *      states.
 *   <li>Specification of {@link TreeTableColumn#minWidthProperty() minWidth}/
 *      {@link TreeTableColumn#prefWidthProperty() prefWidth}/
 *      {@link TreeTableColumn#maxWidthProperty() maxWidth},
 *      and also {@link TreeTableColumn#resizableProperty() fixed width columns}.
 *   <li>Width resizing by the user at runtime.
 *   <li>Column reordering by the user at runtime.
 *   <li>Built-in support for {@link TreeTableColumn#getColumns() column nesting}
 *   </ul>
 * <li>Different {@link #columnResizePolicyProperty() resizing policies} to
 *      dictate what happens when the user resizes columns.
 * <li>Support for {@link #getSortOrder() multiple column sorting} by clicking
 *      the column header (hold down Shift keyboard key whilst clicking on a
 *      header to sort by multiple columns).
 * </ul>
 *
 * <h2>Creating a TreeTableView</h2>
 *
 * <p>Creating a TreeTableView is a multi-step process, and also depends on the
 * underlying data model needing to be represented. For this example we'll use
 * the TreeTableView to visualise a file system, and will therefore make use
 * of an imaginary (and vastly simplified) File class as defined below:
 *
 * <pre>{@code
 * public class File {
 *     private StringProperty name;
 *     public void setName(String value) { nameProperty().set(value); }
 *     public String getName() { return nameProperty().get(); }
 *     public StringProperty nameProperty() {
 *         if (name == null) name = new SimpleStringProperty(this, "name");
 *         return name;
 *     }
 *
 *     private LongProperty lastModified;
 *     public void setLastModified(long value) { lastModifiedProperty().set(value); }
 *     public long getLastModified() { return lastModifiedProperty().get(); }
 *     public LongProperty lastModifiedProperty() {
 *         if (lastModified == null) lastModified = new SimpleLongProperty(this, "lastModified");
 *         return lastModified;
 *     }
 * }}</pre>
 *
 * <p>Firstly, a TreeTableView instance needs to be defined, as such:
 *
 * <pre>{@code
 * TreeTableView<File> treeTable = new TreeTableView<>();}</pre>
 *
 * <p>With the basic TreeTableView instantiated, we next focus on the data model.
 * As mentioned, for this example, we'll be representing a file system using File
 * instances. To do this, we need to define the root node of the tree table, as such:
 *
 * <pre>{@code
 * TreeItem<File> root = new TreeItem<>(new File("/"));
 * treeTable.setRoot(root);}</pre>
 *
 * <p>With the root set as such, the TreeTableView will automatically update whenever
 * the {@link TreeItem#getChildren() children} of the root changes.
 *
 * <p>At this point we now have a TreeTableView hooked up to observe the root
 * TreeItem instance. The missing ingredient
 * now is the means of splitting out the data contained within the model and
 * representing it in one or more {@link TreeTableColumn} instances. To
 * create a two-column TreeTableView to show the file name and last modified
 * properties, we extend the code shown above as follows:
 *
 * <pre>{@code
 * TreeTableColumns<File,String> fileNameCol = new TreeTableColumn<>("Filename");
 * TreeTableColumns<File,Long> lastModifiedCol = new TreeTableColumn<>("Size");
 *
 * table.getColumns().setAll(fileNameCol, lastModifiedCol);}</pre>
 *
 * <p>With the code shown above we have nearly fully defined the minimum properties
 * required to create a TreeTableView instance. The only thing missing is the
 * {@link javafx.scene.control.TreeTableColumn#cellValueFactoryProperty() cell value factories}
 * for the two columns - it is these that are responsible for determining the value
 * of a cell in a given row. Commonly these can be specified using the
 * {@link javafx.scene.control.cell.TreeItemPropertyValueFactory} class, but
 * failing that you can also create an anonymous inner class and do whatever is
 * necessary. For example, using {@link javafx.scene.control.cell.TreeItemPropertyValueFactory}
 * you would do the following:
 *
 * <pre>{@code
 * fileNameCol.setCellValueFactory(new TreeItemPropertyValueFactory("name"));
 * lastModifiedCol.setCellValueFactory(new TreeItemPropertyValueFactory("lastModified"));}</pre>
 *
 * Running this code (assuming the file system structure is probably built up in
 * memory) will result in a TreeTableView being shown with two columns for name
 * and lastModified. Any other properties of the File class will not be shown, as
 * no TreeTableColumns are defined for them.
 *
 * <h3>TreeTableView support for classes that don't contain properties</h3>
 *
 * <p>The code shown above is the shortest possible code for creating a TreeTableView
 * when the domain objects are designed with JavaFX properties in mind
 * (additionally, {@link javafx.scene.control.cell.TreeItemPropertyValueFactory} supports
 * normal JavaBean properties too, although there is a caveat to this, so refer
 * to the class documentation for more information). When this is not the case,
 * it is necessary to provide a custom cell value factory. More information
 * about cell value factories can be found in the {@link TreeTableColumn} API
 * documentation, but briefly, here is how a TreeTableColumns could be specified:
 *
 * <pre>{@code
 * firstNameCol.setCellValueFactory(new Callback<CellDataFeatures<Person, String>, ObservableValue<String>>() {
 *     public ObservableValue<String> call(CellDataFeatures<Person, String> p) {
 *         // p.getValue() returns the TreeItem<Person> instance for a particular TreeTableView row,
 *         // p.getValue().getValue() returns the Person instance inside the TreeItem<Person>
 *         return p.getValue().getValue().firstNameProperty();
 *     }
 *  });
 * }}</pre>
 *
 * <h3>TreeTableView Selection / Focus APIs</h3>
 * <p>To track selection and focus, it is necessary to become familiar with the
 * {@link SelectionModel} and {@link FocusModel} classes. A TreeTableView has at most
 * one instance of each of these classes, available from
 * {@link #selectionModelProperty() selectionModel} and
 * {@link #focusModelProperty() focusModel} properties, respectively.
 * Whilst it is possible to use this API to set a new selection model, in
 * most circumstances this is not necessary - the default selection and focus
 * models should work in most circumstances.
 *
 * <p>The default {@link SelectionModel} used when instantiating a TreeTableView is
 * an implementation of the {@link MultipleSelectionModel} abstract class.
 * However, as noted in the API documentation for
 * the {@link MultipleSelectionModel#selectionModeProperty() selectionMode}
 * property, the default value is {@link SelectionMode#SINGLE}. To enable
 * multiple selection in a default TreeTableView instance, it is therefore necessary
 * to do the following:
 *
 * <pre>
 * {@code
 * treeTableView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);}</pre>
 *
 * <h3>Customizing TreeTableView Visuals</h3>
 * <p>The visuals of the TreeTableView can be entirely customized by replacing the
 * default {@link #rowFactoryProperty() row factory}. A row factory is used to
 * generate {@link TreeTableRow} instances, which are used to represent an entire
 * row in the TreeTableView.
 *
 * <p>In many cases, this is not what is desired however, as it is more commonly
 * the case that cells be customized on a per-column basis, not a per-row basis.
 * It is therefore important to note that a {@link TreeTableRow} is not a
 * {@link TreeTableCell}. A  {@link TreeTableRow} is simply a container for zero or more
 * {@link TreeTableCell}, and in most circumstances it is more likely that you'll
 * want to create custom TreeTableCells, rather than TreeTableRows. The primary use case
 * for creating custom TreeTableRow instances would most probably be to introduce
 * some form of column spanning support.
 *
 * <p>You can create custom {@link TreeTableCell} instances per column by assigning
 * the appropriate function to the TreeTableColumns
 * {@link TreeTableColumn#cellFactoryProperty() cell factory} property.
 *
 * <p>See the {@link Cell} class documentation for a more complete
 * description of how to write custom Cells.
 *
 * <h3>Editing</h3>
 * <p>This control supports inline editing of values, and this section attempts to
 * give an overview of the available APIs and how you should use them.</p>
 *
 * <p>Firstly, cell editing most commonly requires a different user interface
 * than when a cell is not being edited. This is the responsibility of the
 * {@link Cell} implementation being used. For TreeTableView, it is highly
 * recommended that editing be
 * {@link javafx.scene.control.TreeTableColumn#cellFactoryProperty() per-TreeTableColumn},
 * rather than {@link #rowFactoryProperty() per row}, as more often than not
 * you want users to edit each column value differently, and this approach allows
 * for editors specific to each column. It is your choice whether the cell is
 * permanently in an editing state (e.g. this is common for {@link CheckBox} cells),
 * or to switch to a different UI when editing begins (e.g. when a double-click
 * is received on a cell).</p>
 *
 * <p>To know when editing has been requested on a cell,
 * simply override the {@link javafx.scene.control.Cell#startEdit()} method, and
 * update the cell {@link javafx.scene.control.Cell#textProperty() text} and
 * {@link javafx.scene.control.Cell#graphicProperty() graphic} properties as
 * appropriate (e.g. set the text to null and set the graphic to be a
 * {@link TextField}). Additionally, you should also override
 * {@link Cell#cancelEdit()} to reset the UI back to its original visual state
 * when the editing concludes. In both cases it is important that you also
 * ensure that you call the super method to have the cell perform all duties it
 * must do to enter or exit its editing mode.</p>
 *
 * <p>Once your cell is in an editing state, the next thing you are most probably
 * interested in is how to commit or cancel the editing that is taking place. This is your
 * responsibility as the cell factory provider. Your cell implementation will know
 * when the editing is over, based on the user input (e.g. when the user presses
 * the Enter or ESC keys on their keyboard). When this happens, it is your
 * responsibility to call {@link Cell#commitEdit(Object)} or
 * {@link Cell#cancelEdit()}, as appropriate.</p>
 *
 * <p>When you call {@link Cell#commitEdit(Object)} an event is fired to the
 * TreeTableView, which you can observe by adding an {@link EventHandler} via
 * {@link TreeTableColumn#setOnEditCommit(javafx.event.EventHandler)}. Similarly,
 * you can also observe edit events for
 * {@link TreeTableColumn#setOnEditStart(javafx.event.EventHandler) edit start}
 * and {@link TreeTableColumn#setOnEditCancel(javafx.event.EventHandler) edit cancel}.</p>
 *
 * <p>By default the TreeTableColumn edit commit handler is non-null, with a default
 * handler that attempts to overwrite the property value for the
 * item in the currently-being-edited row. It is able to do this as the
 * {@link Cell#commitEdit(Object)} method is passed in the new value, and this
 * is passed along to the edit commit handler via the
 * {@link javafx.scene.control.TreeTableColumn.CellEditEvent CellEditEvent} that is
 * fired. It is simply a matter of calling
 * {@link javafx.scene.control.TreeTableColumn.CellEditEvent#getNewValue()} to
 * retrieve this value.
 *
 * <p>It is very important to note that if you call
 * {@link TreeTableColumn#setOnEditCommit(javafx.event.EventHandler)} with your own
 * {@link EventHandler}, then you will be removing the default handler. Unless
 * you then handle the writeback to the property (or the relevant data source),
 * nothing will happen. You can work around this by using the
 * {@link TreeTableColumn#addEventHandler(javafx.event.EventType, javafx.event.EventHandler)}
 * method to add a {@link TreeTableColumn#EDIT_COMMIT_EVENT} {@link EventType} with
 * your desired {@link EventHandler} as the second argument. Using this method,
 * you will not replace the default implementation, but you will be notified when
 * an edit commit has occurred.</p>
 *
 * <p>Hopefully this summary answers some of the commonly asked questions.
 * Fortunately, JavaFX ships with a number of pre-built cell factories that
 * handle all the editing requirements on your behalf. You can find these
 * pre-built cell factories in the javafx.scene.control.cell package.</p>
 *
 * @see TreeTableColumn
 * @see TreeTablePosition
 * @param <S> The type of the TreeItem instances used in this TreeTableView.
 * @since JavaFX 8.0
 */
@DefaultProperty("root")
public class TreeTableView<S> extends Control {

    /***************************************************************************
     *                                                                         *
     * Constructors                                                            *
     *                                                                         *
     **************************************************************************/

    
Creates an empty TreeTableView.
Refer to the TreeTableView class documentation for details on the default state of other properties. /**
     * Creates an empty TreeTableView.
     *
     * <p>Refer to the {@link TreeTableView} class documentation for details on the
     * default state of other properties.
     */
    public TreeTableView() {
        this(null);
    }

    
Creates a TreeTableView with the provided root node.
Refer to the TreeTableView class documentation for details on the default state of other properties. 
Params:
root – The node to be the root in this TreeTableView./**
     * Creates a TreeTableView with the provided root node.
     *
     * <p>Refer to the {@link TreeTableView} class documentation for details on the
     * default state of other properties.
     *
     * @param root The node to be the root in this TreeTableView.
     */
    public TreeTableView(TreeItem<S> root) {
        getStyleClass().setAll(DEFAULT_STYLE_CLASS);
        setAccessibleRole(AccessibleRole.TREE_TABLE_VIEW);

        setRoot(root);
        updateExpandedItemCount(root);

        // install default selection and focus models - it's unlikely this will be changed
        // by many users.
        setSelectionModel(new TreeTableViewArrayListSelectionModel<S>(this));
        setFocusModel(new TreeTableViewFocusModel<S>(this));

        // we watch the columns list, such that when it changes we can update
        // the leaf columns and visible leaf columns lists (which are read-only).
        getColumns().addListener(weakColumnsObserver);

        // watch for changes to the sort order list - and when it changes run
        // the sort method.
        getSortOrder().addListener((ListChangeListener.Change<? extends TreeTableColumn<S, ?>> c) -> {
            doSort(TableUtil.SortEventType.SORT_ORDER_CHANGE, c);
        });

        // We're watching for changes to the content width such
        // that the resize policy can be run if necessary. This comes from
        // TreeTableViewSkin.
        getProperties().addListener((MapChangeListener<Object, Object>) c -> {
            if (c.wasAdded() && TableView.SET_CONTENT_WIDTH.equals(c.getKey())) {
                if (c.getValueAdded() instanceof Number) {
                    setContentWidth((Double) c.getValueAdded());
                }
                getProperties().remove(TableView.SET_CONTENT_WIDTH);
            }
        });

        isInited = true;
    }



    /***************************************************************************
     *                                                                         *
     * Static properties and methods                                           *
     *                                                                         *
     **************************************************************************/

    
An EventType that indicates some edit event has occurred. It is the parent type of all other edit events: editStartEvent, editCommitEvent and editCancelEvent. 
Type parameters:
<S> – The type of the TreeItem instances used in this TreeTableView
Returns:
An EventType that indicates some edit event has occurred/**
     * An EventType that indicates some edit event has occurred. It is the parent
     * type of all other edit events: {@link #editStartEvent},
     *  {@link #editCommitEvent} and {@link #editCancelEvent}.
     *
     * @param <S> The type of the TreeItem instances used in this TreeTableView
     * @return An EventType that indicates some edit event has occurred
     */
    @SuppressWarnings("unchecked")
    public static <S> EventType<TreeTableView.EditEvent<S>> editAnyEvent() {
        return (EventType<TreeTableView.EditEvent<S>>) EDIT_ANY_EVENT;
    }
    private static final EventType<?> EDIT_ANY_EVENT =
            new EventType<>(Event.ANY, "TREE_TABLE_VIEW_EDIT");

    
An EventType used to indicate that an edit event has started within the
TreeTableView upon which the event was fired.
Type parameters:
<S> – The type of the TreeItem instances used in this TreeTableView
Returns:
An EventType used to indicate that an edit event has started/**
     * An EventType used to indicate that an edit event has started within the
     * TreeTableView upon which the event was fired.
     *
     * @param <S> The type of the TreeItem instances used in this TreeTableView
     * @return An EventType used to indicate that an edit event has started
     */
    @SuppressWarnings("unchecked")
    public static <S> EventType<TreeTableView.EditEvent<S>> editStartEvent() {
        return (EventType<TreeTableView.EditEvent<S>>) EDIT_START_EVENT;
    }
    private static final EventType<?> EDIT_START_EVENT =
            new EventType<>(editAnyEvent(), "EDIT_START");

    
An EventType used to indicate that an edit event has just been canceled
within the TreeTableView upon which the event was fired.
Type parameters:
<S> – The type of the TreeItem instances used in this TreeTableView
Returns:
An EventType used to indicate that an edit event has just been
     canceled/**
     * An EventType used to indicate that an edit event has just been canceled
     * within the TreeTableView upon which the event was fired.
     *
     * @param <S> The type of the TreeItem instances used in this TreeTableView
     * @return An EventType used to indicate that an edit event has just been
     *      canceled
     */
    @SuppressWarnings("unchecked")
    public static <S> EventType<TreeTableView.EditEvent<S>> editCancelEvent() {
        return (EventType<TreeTableView.EditEvent<S>>) EDIT_CANCEL_EVENT;
    }
    private static final EventType<?> EDIT_CANCEL_EVENT =
            new EventType<>(editAnyEvent(), "EDIT_CANCEL");

    
An EventType that is used to indicate that an edit in a TreeTableView has been
committed. This means that user has made changes to the data of a
TreeItem, and that the UI should be updated.
Type parameters:
<S> – The type of the TreeItem instances used in this TreeTableView
Returns:
An EventType that is used to indicate that an edit in a TreeTableView
     has been committed/**
     * An EventType that is used to indicate that an edit in a TreeTableView has been
     * committed. This means that user has made changes to the data of a
     * TreeItem, and that the UI should be updated.
     *
     * @param <S> The type of the TreeItem instances used in this TreeTableView
     * @return An EventType that is used to indicate that an edit in a TreeTableView
     *      has been committed
     */
    @SuppressWarnings("unchecked")
    public static <S> EventType<TreeTableView.EditEvent<S>> editCommitEvent() {
        return (EventType<TreeTableView.EditEvent<S>>) EDIT_COMMIT_EVENT;
    }
    private static final EventType<?> EDIT_COMMIT_EVENT =
            new EventType<>(editAnyEvent(), "EDIT_COMMIT");

    
Returns the number of levels of 'indentation' of the given TreeItem, based on how many times TreeItem.getParent() can be recursively called. If the TreeItem does not have any parent set, the returned value will be zero. For each time getParent() is recursively called, the returned value is incremented by one. 
Important note: This method is deprecated as it does not consider the root node. This means that this method will iterate past the root node of the TreeTableView control, if the root node has a parent. If this is important, call getTreeItemLevel(TreeItem) instead. 
Params:
node – The TreeItem for which the level is needed.
Returns:
An integer representing the number of parents above the given node,
        or -1 if the given TreeItem is null.
Deprecated:
This method does not correctly calculate the distance from the given TreeItem to the root of the TreeTableView. As of JavaFX 8.0_20, the proper way to do this is via getTreeItemLevel(TreeItem)/**
     * Returns the number of levels of 'indentation' of the given TreeItem,
     * based on how many times {@link javafx.scene.control.TreeItem#getParent()}
     * can be recursively called. If the TreeItem does not have any parent set,
     * the returned value will be zero. For each time getParent() is recursively
     * called, the returned value is incremented by one.
     *
     * <p><strong>Important note: </strong>This method is deprecated as it does
     * not consider the root node. This means that this method will iterate
     * past the root node of the TreeTableView control, if the root node has a parent.
     * If this is important, call {@link TreeTableView#getTreeItemLevel(TreeItem)}
     * instead.
     *
     * @param node The TreeItem for which the level is needed.
     * @return An integer representing the number of parents above the given node,
     *         or -1 if the given TreeItem is null.
     * @deprecated This method does not correctly calculate the distance from the
     *          given TreeItem to the root of the TreeTableView. As of JavaFX 8.0_20,
     *          the proper way to do this is via
     *          {@link TreeTableView#getTreeItemLevel(TreeItem)}
     */
    @Deprecated(since="8u20")
    public static int getNodeLevel(TreeItem<?> node) {
        return TreeView.getNodeLevel(node);
    }

    
Very simple resize policy that just resizes the specified column by the
provided delta and shifts all other columns (to the right of the given column)
further to the right (when the delta is positive) or to the left (when the
delta is negative).
It also handles the case where we have nested columns by sharing the new space,
or subtracting the removed space, evenly between all immediate children columns.
Of course, the immediate children may themselves be nested, and they would
then use this policy on their children.
/**
     * <p>Very simple resize policy that just resizes the specified column by the
     * provided delta and shifts all other columns (to the right of the given column)
     * further to the right (when the delta is positive) or to the left (when the
     * delta is negative).
     *
     * <p>It also handles the case where we have nested columns by sharing the new space,
     * or subtracting the removed space, evenly between all immediate children columns.
     * Of course, the immediate children may themselves be nested, and they would
     * then use this policy on their children.
     */
    public static final Callback<TreeTableView.ResizeFeatures, Boolean> UNCONSTRAINED_RESIZE_POLICY =
            new Callback<TreeTableView.ResizeFeatures, Boolean>() {

        @Override public String toString() {
            return "unconstrained-resize";
        }

        @Override public Boolean call(TreeTableView.ResizeFeatures prop) {
            double result = TableUtil.resize(prop.getColumn(), prop.getDelta());
            return Double.compare(result, 0.0) == 0;
        }
    };

    
Simple policy that ensures the width of all visible leaf columns in
this table sum up to equal the width of the table itself.
When the user resizes a column width with this policy, the table automatically
adjusts the width of the right hand side columns. When the user increases a
column width, the table decreases the width of the rightmost column until it
reaches its minimum width. Then it decreases the width of the second
rightmost column until it reaches minimum width and so on. When all right
hand side columns reach minimum size, the user cannot increase the size of
resized column any more.
/**
     * <p>Simple policy that ensures the width of all visible leaf columns in
     * this table sum up to equal the width of the table itself.
     *
     * <p>When the user resizes a column width with this policy, the table automatically
     * adjusts the width of the right hand side columns. When the user increases a
     * column width, the table decreases the width of the rightmost column until it
     * reaches its minimum width. Then it decreases the width of the second
     * rightmost column until it reaches minimum width and so on. When all right
     * hand side columns reach minimum size, the user cannot increase the size of
     * resized column any more.
     */
    public static final Callback<TreeTableView.ResizeFeatures, Boolean> CONSTRAINED_RESIZE_POLICY =
            new Callback<TreeTableView.ResizeFeatures, Boolean>() {

        private boolean isFirstRun = true;

        @Override public String toString() {
            return "constrained-resize";
        }

        @Override public Boolean call(TreeTableView.ResizeFeatures prop) {
            TreeTableView<?> table = prop.getTable();
            List<? extends TableColumnBase<?,?>> visibleLeafColumns = table.getVisibleLeafColumns();
            Boolean result = TableUtil.constrainedResize(prop,
                                               isFirstRun,
                                               table.contentWidth,
                                               visibleLeafColumns);
            isFirstRun = ! isFirstRun ? false : ! result;
            return result;
        }
    };

    
The default sort policy that this TreeTableView will use if no other policy is specified. The sort policy is a simple Callback that accepts a TreeTableView as the sole argument and expects a Boolean response representing whether the sort succeeded or not. A Boolean response of true represents success, and a response of false (or null) will be considered to represent failure. /**
     * The default {@link #sortPolicyProperty() sort policy} that this TreeTableView
     * will use if no other policy is specified. The sort policy is a simple
     * {@link Callback} that accepts a TreeTableView as the sole argument and expects
     * a Boolean response representing whether the sort succeeded or not. A Boolean
     * response of true represents success, and a response of false (or null) will
     * be considered to represent failure.
     */
    public static final Callback<TreeTableView, Boolean> DEFAULT_SORT_POLICY = new Callback<TreeTableView, Boolean>() {
        @Override public Boolean call(TreeTableView table) {
            try {
                TreeItem rootItem = table.getRoot();
                if (rootItem == null) return false;

                TreeSortMode sortMode = table.getSortMode();
                if (sortMode == null) return false;

                rootItem.lastSortMode = sortMode;
                rootItem.lastComparator = table.getComparator();
                rootItem.sort();
                return true;
            } catch (UnsupportedOperationException e) {
                // TODO might need to support other exception types including:
                // ClassCastException - if the class of the specified element prevents it from being added to this list
                // NullPointerException - if the specified element is null and this list does not permit null elements
                // IllegalArgumentException - if some property of this element prevents it from being added to this list

                // If we are here the list does not support sorting, so we gracefully
                // fail the sort request and ensure the UI is put back to its previous
                // state. This is handled in the code that calls the sort policy.

                return false;
            }
        }
    };



    
                                                                        *
Instance Variables                                                      *
                                                                        *
/***************************************************************************
     *                                                                         *
     * Instance Variables                                                      *
     *                                                                         *
     **************************************************************************/

    // used in the tree item modification event listener. Used by the
    // layoutChildren method to determine whether the tree item count should
    // be recalculated.
    private boolean expandedItemCountDirty = true;

    // Used in the getTreeItem(int row) method to act as a cache.
    // See RT-26716 for the justification and performance gains.
    private Map<Integer, SoftReference<TreeItem<S>>> treeItemCacheMap = new HashMap<>();

    // this is the only publicly writable list for columns. This represents the
    // columns as they are given initially by the developer.
    private final ObservableList<TreeTableColumn<S,?>> columns = FXCollections.observableArrayList();

    // Finally, as convenience, we also have an observable list that contains
    // only the leaf columns that are currently visible.
    private final ObservableList<TreeTableColumn<S,?>> visibleLeafColumns = FXCollections.observableArrayList();
    private final ObservableList<TreeTableColumn<S,?>> unmodifiableVisibleLeafColumns = FXCollections.unmodifiableObservableList(visibleLeafColumns);

    // Allows for multiple column sorting based on the order of the TreeTableColumns
    // in this observableArrayList. Each TreeTableColumn is responsible for whether it is
    // sorted using ascending or descending order.
    private ObservableList<TreeTableColumn<S,?>> sortOrder = FXCollections.observableArrayList();

    // width of VirtualFlow minus the vbar width
    // package protected for testing only
    double contentWidth;

    // Used to minimise the amount of work performed prior to the table being
    // completely initialised. In particular it reduces the amount of column
    // resize operations that occur, which slightly improves startup time.
    private boolean isInited = false;



    
                                                                        *
Callbacks and Events                                                    *
                                                                        *
/***************************************************************************
     *                                                                         *
     * Callbacks and Events                                                    *
     *                                                                         *
     **************************************************************************/

    // we use this to forward events that have bubbled up TreeItem instances
    // to the TreeTableViewSkin, to force it to recalculate teh item count and redraw
    // if necessary
    private final EventHandler<TreeItem.TreeModificationEvent<S>> rootEvent = e -> {
        // this forces layoutChildren at the next pulse, and therefore
        // updates the item count if necessary
        EventType<?> eventType = e.getEventType();
        boolean match = false;
        while (eventType != null) {
            if (eventType.equals(TreeItem.<S>expandedItemCountChangeEvent())) {
                match = true;
                break;
            }
            eventType = eventType.getSuperType();
        }

        if (match) {
            expandedItemCountDirty = true;
            requestLayout();
        }
    };

    private final ListChangeListener<TreeTableColumn<S,?>> columnsObserver = new ListChangeListener<TreeTableColumn<S,?>>() {
        @Override public void onChanged(ListChangeListener.Change<? extends TreeTableColumn<S,?>> c) {
            final List<TreeTableColumn<S,?>> columns = getColumns();

            // Fix for RT-39822 - don't allow the same column to be installed twice
            while (c.next()) {
                if (c.wasAdded()) {
                    List<TreeTableColumn<S,?>> duplicates = new ArrayList<>();
                    for (TreeTableColumn<S,?> addedColumn : c.getAddedSubList()) {
                        if (addedColumn == null) continue;

                        int count = 0;
                        for (TreeTableColumn<S,?> column : columns) {
                            if (addedColumn == column) {
                                count++;
                            }
                        }

                        if (count > 1) {
                            duplicates.add(addedColumn);
                        }
                    }

                    if (!duplicates.isEmpty()) {
                        String titleList = "";
                        for (TreeTableColumn<S,?> dupe : duplicates) {
                            titleList += "'" + dupe.getText() + "', ";
                        }
                        throw new IllegalStateException("Duplicate TreeTableColumns detected in TreeTableView columns list with titles " + titleList);
                    }
                }
            }
            c.reset();

            // Fix for RT-15194: Need to remove removed columns from the
            // sortOrder list.
            List<TreeTableColumn<S,?>> toRemove = new ArrayList<TreeTableColumn<S,?>>();
            while (c.next()) {
                final List<? extends TreeTableColumn<S, ?>> removed = c.getRemoved();
                final List<? extends TreeTableColumn<S, ?>> added = c.getAddedSubList();

                if (c.wasRemoved()) {
                    toRemove.addAll(removed);
                    for (TreeTableColumn<S,?> tc : removed) {
                        tc.setTreeTableView(null);
                    }
                }

                if (c.wasAdded()) {
                    toRemove.removeAll(added);
                    for (TreeTableColumn<S,?> tc : added) {
                        tc.setTreeTableView(TreeTableView.this);
                    }
                }

                // set up listeners
                TableUtil.removeColumnsListener(removed, weakColumnsObserver);
                TableUtil.addColumnsListener(added, weakColumnsObserver);

                TableUtil.removeTableColumnListener(c.getRemoved(),
                        weakColumnVisibleObserver,
                        weakColumnSortableObserver,
                        weakColumnSortTypeObserver,
                        weakColumnComparatorObserver);
                TableUtil.addTableColumnListener(c.getAddedSubList(),
                        weakColumnVisibleObserver,
                        weakColumnSortableObserver,
                        weakColumnSortTypeObserver,
                        weakColumnComparatorObserver);
            }

            // We don't maintain a bind for leafColumns, we simply call this update
            // function behind the scenes in the appropriate places.
            updateVisibleLeafColumns();

            sortOrder.removeAll(toRemove);

            // Fix for RT-38892.
            final TreeTableViewFocusModel<S> fm = getFocusModel();
            final TreeTableViewSelectionModel<S> sm = getSelectionModel();
            c.reset();

            // we need to collect together all removed and all added columns, because
            // the code below works on the actually removed columns. If we perform
            // the code within this while loop, we'll be deselecting columns that
            // should be deselected (because they have just moved place, for example).
            List<TreeTableColumn<S,?>> removed = new ArrayList<>();
            List<TreeTableColumn<S,?>> added = new ArrayList<>();
            while (c.next()) {
                if (c.wasRemoved()) {
                    removed.addAll(c.getRemoved());
                }
                if (c.wasAdded()) {
                    added.addAll(c.getAddedSubList());
                }
            }
            removed.removeAll(added);


            // Fix for focus - we simply move focus to a cell to the left
            // of the focused cell if the focused cell was located within
            // a column that has been removed.
            if (fm != null) {
                TreeTablePosition<S, ?> focusedCell = fm.getFocusedCell();
                boolean match = false;
                for (TreeTableColumn<S, ?> tc : removed) {
                    match = focusedCell != null && focusedCell.getTableColumn() == tc;
                    if (match) {
                        break;
                    }
                }

                if (match) {
                    int matchingColumnIndex = lastKnownColumnIndex.getOrDefault(focusedCell.getTableColumn(), 0);
                    int newFocusColumnIndex =
                            matchingColumnIndex == 0 ? 0 :
                                    Math.min(getVisibleLeafColumns().size() - 1, matchingColumnIndex - 1);
                    fm.focus(focusedCell.getRow(), getVisibleLeafColumn(newFocusColumnIndex));
                }
            }

            // Fix for selection - we remove selection from all cells that
            // were within the removed column.
            if (sm != null) {
                List<TreeTablePosition> selectedCells = new ArrayList<>(sm.getSelectedCells());
                for (TreeTablePosition selectedCell : selectedCells) {
                    boolean match = false;
                    for (TreeTableColumn<S, ?> tc : removed) {
                        match = selectedCell != null && selectedCell.getTableColumn() == tc;
                        if (match) break;
                    }

                    if (match) {
                        // we can't just use the selectedCell.getTableColumn(), as that
                        // column no longer exists and therefore its index is not correct.
                        int matchingColumnIndex = lastKnownColumnIndex.getOrDefault(selectedCell.getTableColumn(), -1);
                        if (matchingColumnIndex == -1) continue;

                        if (sm instanceof TreeTableViewArrayListSelectionModel) {
                            // Also, because the table column no longer exists in the columns
                            // list at this point, we can't just call:
                            // sm.clearSelection(selectedCell.getRow(), selectedCell.getTableColumn());
                            // as the tableColumn would map to an index of -1, which means that
                            // selection will not be cleared. Instead, we have to create
                            // a new TablePosition with a fixed column index and use that.
                            TreeTablePosition<S,?> fixedTablePosition =
                                    new TreeTablePosition<S,Object>(TreeTableView.this,
                                            selectedCell.getRow(),
                                            selectedCell.getTableColumn());
                            fixedTablePosition.fixedColumnIndex = matchingColumnIndex;

                            ((TreeTableViewArrayListSelectionModel)sm).clearSelection(fixedTablePosition);
                        } else {
                            sm.clearSelection(selectedCell.getRow(), selectedCell.getTableColumn());
                        }
                    }
                }
            }


            // update the lastKnownColumnIndex map
            lastKnownColumnIndex.clear();
            for (TreeTableColumn<S,?> tc : getColumns()) {
                int index = getVisibleLeafIndex(tc);
                if (index > -1) {
                    lastKnownColumnIndex.put(tc, index);
                }
            }
        }
    };

    private final WeakHashMap<TreeTableColumn<S,?>, Integer> lastKnownColumnIndex = new WeakHashMap<>();

    private final InvalidationListener columnVisibleObserver = valueModel -> {
        updateVisibleLeafColumns();
    };

    private final InvalidationListener columnSortableObserver = valueModel -> {
        TreeTableColumn col = (TreeTableColumn) ((BooleanProperty)valueModel).getBean();
        if (! getSortOrder().contains(col)) return;
        doSort(TableUtil.SortEventType.COLUMN_SORTABLE_CHANGE, col);
    };

    private final InvalidationListener columnSortTypeObserver = valueModel -> {
        TreeTableColumn col = (TreeTableColumn) ((ObjectProperty)valueModel).getBean();
        if (! getSortOrder().contains(col)) return;
        doSort(TableUtil.SortEventType.COLUMN_SORT_TYPE_CHANGE, col);
    };

    private final InvalidationListener columnComparatorObserver = valueModel -> {
        TreeTableColumn col = (TreeTableColumn) ((SimpleObjectProperty)valueModel).getBean();
        if (! getSortOrder().contains(col)) return;
        doSort(TableUtil.SortEventType.COLUMN_COMPARATOR_CHANGE, col);
    };

    /* proxy pseudo-class state change from selectionModel's cellSelectionEnabledProperty */
    private final InvalidationListener cellSelectionModelInvalidationListener = o -> {
        boolean isCellSelection = ((BooleanProperty)o).get();
        pseudoClassStateChanged(PSEUDO_CLASS_CELL_SELECTION,  isCellSelection);
        pseudoClassStateChanged(PSEUDO_CLASS_ROW_SELECTION,  !isCellSelection);
    };

    private WeakEventHandler<TreeItem.TreeModificationEvent<S>> weakRootEventListener;

    private final WeakInvalidationListener weakColumnVisibleObserver =
            new WeakInvalidationListener(columnVisibleObserver);

    private final WeakInvalidationListener weakColumnSortableObserver =
            new WeakInvalidationListener(columnSortableObserver);

    private final WeakInvalidationListener weakColumnSortTypeObserver =
            new WeakInvalidationListener(columnSortTypeObserver);

    private final WeakInvalidationListener weakColumnComparatorObserver =
            new WeakInvalidationListener(columnComparatorObserver);

    private final WeakListChangeListener<TreeTableColumn<S,?>> weakColumnsObserver =
            new WeakListChangeListener<TreeTableColumn<S,?>>(columnsObserver);

    private final WeakInvalidationListener weakCellSelectionModelInvalidationListener =
            new WeakInvalidationListener(cellSelectionModelInvalidationListener);



    
                                                                        *
Properties                                                              *
                                                                        *
/***************************************************************************
     *                                                                         *
     * Properties                                                              *
     *                                                                         *
     **************************************************************************/

    // --- Root
    private ObjectProperty<TreeItem<S>> root = new SimpleObjectProperty<TreeItem<S>>(this, "root") {
        private WeakReference<TreeItem<S>> weakOldItem;

        @Override protected void invalidated() {
            TreeItem<S> oldTreeItem = weakOldItem == null ? null : weakOldItem.get();
            if (oldTreeItem != null && weakRootEventListener != null) {
                oldTreeItem.removeEventHandler(TreeItem.<S>treeNotificationEvent(), weakRootEventListener);
            }

            TreeItem<S> root = getRoot();
            if (root != null) {
                weakRootEventListener = new WeakEventHandler<>(rootEvent);
                getRoot().addEventHandler(TreeItem.<S>treeNotificationEvent(), weakRootEventListener);
                weakOldItem = new WeakReference<>(root);
            }

            // Fix for RT-35763
            getSortOrder().clear();

            expandedItemCountDirty = true;
            updateRootExpanded();
        }
    };

    
Sets the root node in this TreeTableView. See the TreeItem class level documentation for more details. 
Params:
value – The TreeItem that will be placed at the root of the TreeTableView./**
     * Sets the root node in this TreeTableView. See the {@link TreeItem} class level
     * documentation for more details.
     *
     * @param value The {@link TreeItem} that will be placed at the root of the
     *      TreeTableView.
     */
    public final void setRoot(TreeItem<S> value) {
        rootProperty().set(value);
    }

    
Returns the current root node of this TreeTableView, or null if no root node
is specified.
Returns:
The current root node, or null if no root node exists./**
     * Returns the current root node of this TreeTableView, or null if no root node
     * is specified.
     * @return The current root node, or null if no root node exists.
     */
    public final TreeItem<S> getRoot() {
        return root == null ? null : root.get();
    }

    
Property representing the root node of the TreeTableView.
Returns:
the root property/**
     * Property representing the root node of the TreeTableView.
     * @return the root property
     */
    public final ObjectProperty<TreeItem<S>> rootProperty() {
        return root;
    }



    // --- Show Root
    private BooleanProperty showRoot;

    
Specifies whether the root TreeItem should be shown within this TreeTableView. 
Params:
value – If true, the root TreeItem will be shown, and if false it
     will be hidden./**
     * Specifies whether the root {@code TreeItem} should be shown within this
     * TreeTableView.
     *
     * @param value If true, the root TreeItem will be shown, and if false it
     *      will be hidden.
     */
    public final void setShowRoot(boolean value) {
        showRootProperty().set(value);
    }

    
Returns true if the root of the TreeTableView should be shown, and false if
it should not. By default, the root TreeItem is visible in the TreeTableView.
Returns:
true if the root of the TreeTableView should be shown/**
     * Returns true if the root of the TreeTableView should be shown, and false if
     * it should not. By default, the root TreeItem is visible in the TreeTableView.
     * @return true if the root of the TreeTableView should be shown
     */
    public final boolean isShowRoot() {
        return showRoot == null ? true : showRoot.get();
    }

    
Property that represents whether or not the TreeTableView root node is visible.
Returns:
the show root property/**
     * Property that represents whether or not the TreeTableView root node is visible.
     * @return the show root property
     */
    public final BooleanProperty showRootProperty() {
        if (showRoot == null) {
            showRoot = new SimpleBooleanProperty(this, "showRoot", true) {
                @Override protected void invalidated() {
                    updateRootExpanded();
                    updateExpandedItemCount(getRoot());
                }
            };
        }
        return showRoot;
    }



    // --- Tree Column
    private ObjectProperty<TreeTableColumn<S,?>> treeColumn;
    
Property that represents which column should have the disclosure node shown in it (that is, the column with the arrow). By default this will be the left-most column if this property is null, otherwise it will be the specified column assuming it is non-null and contained within the visible leaf columns list. 
Returns:
the tree column property/**
     * Property that represents which column should have the disclosure node
     * shown in it (that is, the column with the arrow). By default this will be
     * the left-most column if this property is null, otherwise it will be the
     * specified column assuming it is non-null and contained within the
     * {@link #getVisibleLeafColumns() visible leaf columns} list.
     * @return the tree column property
     */
    public final ObjectProperty<TreeTableColumn<S,?>> treeColumnProperty() {
        if (treeColumn == null) {
            treeColumn = new SimpleObjectProperty<>(this, "treeColumn", null);
        }
        return treeColumn;
    }
    public final void setTreeColumn(TreeTableColumn<S,?> value) {
        treeColumnProperty().set(value);
    }
    public final TreeTableColumn<S,?> getTreeColumn() {
        return treeColumn == null ? null : treeColumn.get();
    }



    // --- Selection Model
    private ObjectProperty<TreeTableViewSelectionModel<S>> selectionModel;

    
Sets the MultipleSelectionModel to be used in the TreeTableView. Despite a TreeTableView requiring a MultipleSelectionModel, it is possible to configure it to only allow single selection (see MultipleSelectionModel.setSelectionMode(SelectionMode) for more information). 
Params:
value – the MultipleSelectionModel to be used/**
     * Sets the {@link MultipleSelectionModel} to be used in the TreeTableView.
     * Despite a TreeTableView requiring a <code><b>Multiple</b>SelectionModel</code>,
     * it is possible to configure it to only allow single selection (see
     * {@link MultipleSelectionModel#setSelectionMode(javafx.scene.control.SelectionMode)}
     * for more information).
     * @param value the {@link MultipleSelectionModel} to be used
     */
    public final void setSelectionModel(TreeTableViewSelectionModel<S> value) {
        selectionModelProperty().set(value);
    }

    
Returns the currently installed selection model.
Returns:
the currently installed selection model/**
     * Returns the currently installed selection model.
     * @return the currently installed selection model
     */
    public final TreeTableViewSelectionModel<S> getSelectionModel() {
        return selectionModel == null ? null : selectionModel.get();
    }

    
The SelectionModel provides the API through which it is possible
to select single or multiple items within a TreeTableView, as  well as inspect
which rows have been selected by the user. Note that it has a generic
type that must match the type of the TreeTableView itself.
Returns:
the selection model property/**
     * The SelectionModel provides the API through which it is possible
     * to select single or multiple items within a TreeTableView, as  well as inspect
     * which rows have been selected by the user. Note that it has a generic
     * type that must match the type of the TreeTableView itself.
     * @return the selection model property
     */
    public final ObjectProperty<TreeTableViewSelectionModel<S>> selectionModelProperty() {
        if (selectionModel == null) {
            selectionModel = new SimpleObjectProperty<TreeTableViewSelectionModel<S>>(this, "selectionModel") {

                TreeTableViewSelectionModel<S> oldValue = null;

                @Override protected void invalidated() {
                    // need to listen to the cellSelectionEnabledProperty
                    // in order to set pseudo-class state
                    if (oldValue != null) {
                        oldValue.cellSelectionEnabledProperty().removeListener(weakCellSelectionModelInvalidationListener);

                        if (oldValue instanceof TreeTableViewArrayListSelectionModel) {
                            ((TreeTableViewArrayListSelectionModel)oldValue).dispose();
                        }
                    }

                    oldValue = get();

                    if (oldValue != null) {
                        oldValue.cellSelectionEnabledProperty().addListener(weakCellSelectionModelInvalidationListener);
                        // fake invalidation to ensure updated pseudo-class states
                        weakCellSelectionModelInvalidationListener.invalidated(oldValue.cellSelectionEnabledProperty());
                    }
                }
            };
        }
        return selectionModel;
    }


    // --- Focus Model
    private ObjectProperty<TreeTableViewFocusModel<S>> focusModel;

    
Sets the FocusModel to be used in the TreeTableView. 
Params:
value – the FocusModel to be used/**
     * Sets the {@link FocusModel} to be used in the TreeTableView.
     * @param value the {@link FocusModel} to be used
     */
    public final void setFocusModel(TreeTableViewFocusModel<S> value) {
        focusModelProperty().set(value);
    }

    
Returns the currently installed FocusModel. 
Returns:
the currently installed FocusModel/**
     * Returns the currently installed {@link FocusModel}.
     * @return the currently installed {@link FocusModel}
     */
    public final TreeTableViewFocusModel<S> getFocusModel() {
        return focusModel == null ? null : focusModel.get();
    }

    
The FocusModel provides the API through which it is possible
to control focus on zero or one rows of the TreeTableView. Generally the
default implementation should be more than sufficient.
Returns:
the focus model property/**
     * The FocusModel provides the API through which it is possible
     * to control focus on zero or one rows of the TreeTableView. Generally the
     * default implementation should be more than sufficient.
     * @return the focus model property
     */
    public final ObjectProperty<TreeTableViewFocusModel<S>> focusModelProperty() {
        if (focusModel == null) {
            focusModel = new SimpleObjectProperty<TreeTableViewFocusModel<S>>(this, "focusModel");
        }
        return focusModel;
    }


    // --- Tree node count
    
Represents the number of tree nodes presently able to be visible in the
TreeTableView. This is essentially the count of all expanded tree items, and
their children.
For example, if just the root node is visible, the expandedItemCount will
be one. If the root had three children and the root was expanded, the value
will be four.
/**
     * <p>Represents the number of tree nodes presently able to be visible in the
     * TreeTableView. This is essentially the count of all expanded tree items, and
     * their children.
     *
     * <p>For example, if just the root node is visible, the expandedItemCount will
     * be one. If the root had three children and the root was expanded, the value
     * will be four.
     */
    private ReadOnlyIntegerWrapper expandedItemCount = new ReadOnlyIntegerWrapper(this, "expandedItemCount", 0);
    public final ReadOnlyIntegerProperty expandedItemCountProperty() {
        return expandedItemCount.getReadOnlyProperty();
    }
    private void setExpandedItemCount(int value) {
        expandedItemCount.set(value);
    }
    public final int getExpandedItemCount() {
        if (expandedItemCountDirty) {
            updateExpandedItemCount(getRoot());
        }
        return expandedItemCount.get();
    }


    // --- Editable
    private BooleanProperty editable;
    public final void setEditable(boolean value) {
        editableProperty().set(value);
    }
    public final boolean isEditable() {
        return editable == null ? false : editable.get();
    }
    
Specifies whether this TreeTableView is editable - only if the TreeTableView and
the TreeCells within it are both editable will a TreeCell be able to go
into their editing state.
Returns:
the editable property/**
     * Specifies whether this TreeTableView is editable - only if the TreeTableView and
     * the TreeCells within it are both editable will a TreeCell be able to go
     * into their editing state.
     * @return the editable property
     */
    public final BooleanProperty editableProperty() {
        if (editable == null) {
            editable = new SimpleBooleanProperty(this, "editable", false);
        }
        return editable;
    }


    // --- Editing Cell
    private ReadOnlyObjectWrapper<TreeTablePosition<S,?>> editingCell;
    private void setEditingCell(TreeTablePosition<S,?> value) {
        editingCellPropertyImpl().set(value);
    }
    public final TreeTablePosition<S,?> getEditingCell() {
        return editingCell == null ? null : editingCell.get();
    }

    
Represents the current cell being edited, or null if
there is no cell being edited.
Returns:
the editing cell property/**
     * Represents the current cell being edited, or null if
     * there is no cell being edited.
     * @return the editing cell property
     */
    public final ReadOnlyObjectProperty<TreeTablePosition<S,?>> editingCellProperty() {
        return editingCellPropertyImpl().getReadOnlyProperty();
    }

    private ReadOnlyObjectWrapper<TreeTablePosition<S,?>> editingCellPropertyImpl() {
        if (editingCell == null) {
            editingCell = new ReadOnlyObjectWrapper<TreeTablePosition<S,?>>(this, "editingCell");
        }
        return editingCell;
    }


    // --- Table menu button visible
    private BooleanProperty tableMenuButtonVisible;
    
This controls whether a menu button is available when the user clicks
in a designated space within the TableView, within which is a radio menu
item for each TreeTableColumn in this table. This menu allows for the user to
show and hide all TreeTableColumns easily.
Returns:
the table menu button visible property/**
     * This controls whether a menu button is available when the user clicks
     * in a designated space within the TableView, within which is a radio menu
     * item for each TreeTableColumn in this table. This menu allows for the user to
     * show and hide all TreeTableColumns easily.
     * @return the table menu button visible property
     */
    public final BooleanProperty tableMenuButtonVisibleProperty() {
        if (tableMenuButtonVisible == null) {
            tableMenuButtonVisible = new SimpleBooleanProperty(this, "tableMenuButtonVisible");
        }
        return tableMenuButtonVisible;
    }
    public final void setTableMenuButtonVisible (boolean value) {
        tableMenuButtonVisibleProperty().set(value);
    }
    public final boolean isTableMenuButtonVisible() {
        return tableMenuButtonVisible == null ? false : tableMenuButtonVisible.get();
    }


    // --- Column Resize Policy
    private ObjectProperty<Callback<TreeTableView.ResizeFeatures, Boolean>> columnResizePolicy;
    public final void setColumnResizePolicy(Callback<TreeTableView.ResizeFeatures, Boolean> callback) {
        columnResizePolicyProperty().set(callback);
    }
    public final Callback<TreeTableView.ResizeFeatures, Boolean> getColumnResizePolicy() {
        return columnResizePolicy == null ? UNCONSTRAINED_RESIZE_POLICY : columnResizePolicy.get();
    }

    
This is the function called when the user completes a column-resize operation. The two most common policies are available as static functions in the TableView class: TreeTableView<S>.UNCONSTRAINED_RESIZE_POLICY and TreeTableView<S>.CONSTRAINED_RESIZE_POLICY. 
Returns:
the column resize policy property/**
     * This is the function called when the user completes a column-resize
     * operation. The two most common policies are available as static functions
     * in the TableView class: {@link #UNCONSTRAINED_RESIZE_POLICY} and
     * {@link #CONSTRAINED_RESIZE_POLICY}.
     * @return the column resize policy property
     */
    public final ObjectProperty<Callback<TreeTableView.ResizeFeatures, Boolean>> columnResizePolicyProperty() {
        if (columnResizePolicy == null) {
            columnResizePolicy = new SimpleObjectProperty<Callback<TreeTableView.ResizeFeatures, Boolean>>(this, "columnResizePolicy", UNCONSTRAINED_RESIZE_POLICY) {
                private Callback<TreeTableView.ResizeFeatures, Boolean> oldPolicy;

                @Override protected void invalidated() {
                    if (isInited) {
                        get().call(new TreeTableView.ResizeFeatures(TreeTableView.this, null, 0.0));

                        if (oldPolicy != null) {
                            PseudoClass state = PseudoClass.getPseudoClass(oldPolicy.toString());
                            pseudoClassStateChanged(state, false);
                        }
                        if (get() != null) {
                            PseudoClass state = PseudoClass.getPseudoClass(get().toString());
                            pseudoClassStateChanged(state, true);
                        }
                        oldPolicy = get();
                    }
                }
            };
        }
        return columnResizePolicy;
    }


    // --- Row Factory
    private ObjectProperty<Callback<TreeTableView<S>, TreeTableRow<S>>> rowFactory;

    
A function which produces a TreeTableRow. The system is responsible for
reusing TreeTableRows. Return from this function a TreeTableRow which
might be usable for representing a single row in a TableView.

Note that a TreeTableRow is not a TableCell. A TreeTableRow is
simply a container for a TableCell, and in most circumstances it is more
likely that you'll want to create custom TableCells, rather than
TreeTableRows. The primary use case for creating custom TreeTableRow
instances would most probably be to introduce some form of column
spanning support.

You can create custom TableCell instances per column by assigning the
appropriate function to the cellFactory property in the TreeTableColumn class.
Returns:
the row factory property/**
     * A function which produces a TreeTableRow. The system is responsible for
     * reusing TreeTableRows. Return from this function a TreeTableRow which
     * might be usable for representing a single row in a TableView.
     * <p>
     * Note that a TreeTableRow is <b>not</b> a TableCell. A TreeTableRow is
     * simply a container for a TableCell, and in most circumstances it is more
     * likely that you'll want to create custom TableCells, rather than
     * TreeTableRows. The primary use case for creating custom TreeTableRow
     * instances would most probably be to introduce some form of column
     * spanning support.
     * <p>
     * You can create custom TableCell instances per column by assigning the
     * appropriate function to the cellFactory property in the TreeTableColumn class.
     * @return the row factory property
     */
    public final ObjectProperty<Callback<TreeTableView<S>, TreeTableRow<S>>> rowFactoryProperty() {
        if (rowFactory == null) {
            rowFactory = new SimpleObjectProperty<Callback<TreeTableView<S>, TreeTableRow<S>>>(this, "rowFactory");
        }
        return rowFactory;
    }
    public final void setRowFactory(Callback<TreeTableView<S>, TreeTableRow<S>> value) {
        rowFactoryProperty().set(value);
    }
    public final Callback<TreeTableView<S>, TreeTableRow<S>> getRowFactory() {
        return rowFactory == null ? null : rowFactory.get();
    }


    // --- Placeholder Node
    private ObjectProperty<Node> placeholder;
    
This Node is shown to the user when the table has no content to show.
This may be the case because the table model has no data in the first
place, that a filter has been applied to the table model, resulting
in there being nothing to show the user, or that there are no currently
visible columns.
Returns:
the placeholder property/**
     * This Node is shown to the user when the table has no content to show.
     * This may be the case because the table model has no data in the first
     * place, that a filter has been applied to the table model, resulting
     * in there being nothing to show the user, or that there are no currently
     * visible columns.
     * @return the placeholder property
     */
    public final ObjectProperty<Node> placeholderProperty() {
        if (placeholder == null) {
            placeholder = new SimpleObjectProperty<Node>(this, "placeholder");
        }
        return placeholder;
    }
    public final void setPlaceholder(Node value) {
        placeholderProperty().set(value);
    }
    public final Node getPlaceholder() {
        return placeholder == null ? null : placeholder.get();
    }


    // --- Fixed cell size
    private DoubleProperty fixedCellSize;

    
Sets the new fixed cell size for this control. Any value greater than
zero will enable fixed cell size mode, whereas a zero or negative value
(or Region.USE_COMPUTED_SIZE) will be used to disabled fixed cell size
mode.
Params:
value – The new fixed cell size value, or a value less than or equal
             to zero (or Region.USE_COMPUTED_SIZE) to disable.
Since:
JavaFX 8.0/**
     * Sets the new fixed cell size for this control. Any value greater than
     * zero will enable fixed cell size mode, whereas a zero or negative value
     * (or Region.USE_COMPUTED_SIZE) will be used to disabled fixed cell size
     * mode.
     *
     * @param value The new fixed cell size value, or a value less than or equal
     *              to zero (or Region.USE_COMPUTED_SIZE) to disable.
     * @since JavaFX 8.0
     */
    public final void setFixedCellSize(double value) {
        fixedCellSizeProperty().set(value);
    }

    
Returns the fixed cell size value. A value less than or equal to zero is
used to represent that fixed cell size mode is disabled, and a value
greater than zero represents the size of all cells in this control.
Returns:
A double representing the fixed cell size of this control, or a
     value less than or equal to zero if fixed cell size mode is disabled.
Since:
JavaFX 8.0/**
     * Returns the fixed cell size value. A value less than or equal to zero is
     * used to represent that fixed cell size mode is disabled, and a value
     * greater than zero represents the size of all cells in this control.
     *
     * @return A double representing the fixed cell size of this control, or a
     *      value less than or equal to zero if fixed cell size mode is disabled.
     * @since JavaFX 8.0
     */
    public final double getFixedCellSize() {
        return fixedCellSize == null ? Region.USE_COMPUTED_SIZE : fixedCellSize.get();
    }
    
Specifies whether this control has cells that are a fixed height (of the
specified value). If this value is less than or equal to zero,
then all cells are individually sized and positioned. This is a slow
operation. Therefore, when performance matters and developers are not
dependent on variable cell sizes it is a good idea to set the fixed cell
size value. Generally cells are around 24px, so setting a fixed cell size
of 24 is likely to result in very little difference in visuals, but a
improvement to performance.
To set this property via CSS, use the -fx-fixed-cell-size property.
This should not be confused with the -fx-cell-size property. The difference
between these two CSS properties is that -fx-cell-size will size all
cells to the specified size, but it will not enforce that this is the
only size (thus allowing for variable cell sizes, and preventing the
performance gains from being possible). Therefore, when performance matters
use -fx-fixed-cell-size, instead of -fx-cell-size. If both properties are
specified in CSS, -fx-fixed-cell-size takes precedence.
Returns:
the fixed cell size property
Since:
JavaFX 8.0/**
     * Specifies whether this control has cells that are a fixed height (of the
     * specified value). If this value is less than or equal to zero,
     * then all cells are individually sized and positioned. This is a slow
     * operation. Therefore, when performance matters and developers are not
     * dependent on variable cell sizes it is a good idea to set the fixed cell
     * size value. Generally cells are around 24px, so setting a fixed cell size
     * of 24 is likely to result in very little difference in visuals, but a
     * improvement to performance.
     *
     * <p>To set this property via CSS, use the -fx-fixed-cell-size property.
     * This should not be confused with the -fx-cell-size property. The difference
     * between these two CSS properties is that -fx-cell-size will size all
     * cells to the specified size, but it will not enforce that this is the
     * only size (thus allowing for variable cell sizes, and preventing the
     * performance gains from being possible). Therefore, when performance matters
     * use -fx-fixed-cell-size, instead of -fx-cell-size. If both properties are
     * specified in CSS, -fx-fixed-cell-size takes precedence.</p>
     *
     * @return the fixed cell size property
     * @since JavaFX 8.0
     */
    public final DoubleProperty fixedCellSizeProperty() {
        if (fixedCellSize == null) {
            fixedCellSize = new StyleableDoubleProperty(Region.USE_COMPUTED_SIZE) {
                @Override public CssMetaData<TreeTableView<?>,Number> getCssMetaData() {
                    return StyleableProperties.FIXED_CELL_SIZE;
                }

                @Override public Object getBean() {
                    return TreeTableView.this;
                }

                @Override public String getName() {
                    return "fixedCellSize";
                }
            };
        }
        return fixedCellSize;
    }


    // --- SortMode
    
Specifies the sort mode to use when sorting the contents of this TreeTableView, should any columns be specified in the sort order list. /**
     * Specifies the sort mode to use when sorting the contents of this TreeTableView,
     * should any columns be specified in the {@link #getSortOrder() sort order}
     * list.
     */
    private ObjectProperty<TreeSortMode> sortMode;
    public final ObjectProperty<TreeSortMode> sortModeProperty() {
        if (sortMode == null) {
            sortMode = new SimpleObjectProperty<>(this, "sortMode", TreeSortMode.ALL_DESCENDANTS);
        }
        return sortMode;
    }
    public final void setSortMode(TreeSortMode value) {
        sortModeProperty().set(value);
    }
    public final TreeSortMode getSortMode() {
        return sortMode == null ? TreeSortMode.ALL_DESCENDANTS : sortMode.get();
    }


    // --- Comparator (built via sortOrder list, so read-only)
    
The comparator property is a read-only property that is representative of the current state of the sort order list. The sort order list contains the columns that have been added to it either programmatically or via a user clicking on the headers themselves. /**
     * The comparator property is a read-only property that is representative of the
     * current state of the {@link #getSortOrder() sort order} list. The sort
     * order list contains the columns that have been added to it either programmatically
     * or via a user clicking on the headers themselves.
     */
    private ReadOnlyObjectWrapper<Comparator<TreeItem<S>>> comparator;
    private void setComparator(Comparator<TreeItem<S>> value) {
        comparatorPropertyImpl().set(value);
    }
    public final Comparator<TreeItem<S>> getComparator() {
        return comparator == null ? null : comparator.get();
    }
    public final ReadOnlyObjectProperty<Comparator<TreeItem<S>>> comparatorProperty() {
        return comparatorPropertyImpl().getReadOnlyProperty();
    }
    private ReadOnlyObjectWrapper<Comparator<TreeItem<S>>> comparatorPropertyImpl() {
        if (comparator == null) {
            comparator = new ReadOnlyObjectWrapper<>(this, "comparator");
        }
        return comparator;
    }


    // --- sortPolicy
    
The sort policy specifies how sorting in this TreeTableView should be performed.
For example, a basic sort policy may just recursively sort the children of
the root tree item, whereas a more advanced sort policy may call to a
database to perform the necessary sorting on the server-side.
TreeTableView ships with a default
sort policy that does precisely as mentioned above: it simply attempts to sort the tree hierarchy in-place. 
It is recommended that rather than override the sort method that a different sort policy be provided instead. /**
     * The sort policy specifies how sorting in this TreeTableView should be performed.
     * For example, a basic sort policy may just recursively sort the children of
     * the root tree item, whereas a more advanced sort policy may call to a
     * database to perform the necessary sorting on the server-side.
     *
     * <p>TreeTableView ships with a {@link TableView#DEFAULT_SORT_POLICY default
     * sort policy} that does precisely as mentioned above: it simply attempts
     * to sort the tree hierarchy in-place.
     *
     * <p>It is recommended that rather than override the {@link TreeTableView#sort() sort}
     * method that a different sort policy be provided instead.
     */
    private ObjectProperty<Callback<TreeTableView<S>, Boolean>> sortPolicy;
    public final void setSortPolicy(Callback<TreeTableView<S>, Boolean> callback) {
        sortPolicyProperty().set(callback);
    }
    @SuppressWarnings("unchecked")
    public final Callback<TreeTableView<S>, Boolean> getSortPolicy() {
        return sortPolicy == null ?
                (Callback<TreeTableView<S>, Boolean>)(Object) DEFAULT_SORT_POLICY :
                sortPolicy.get();
    }
    @SuppressWarnings("unchecked")
    public final ObjectProperty<Callback<TreeTableView<S>, Boolean>> sortPolicyProperty() {
        if (sortPolicy == null) {
            sortPolicy = new SimpleObjectProperty<Callback<TreeTableView<S>, Boolean>>(
                    this, "sortPolicy", (Callback<TreeTableView<S>, Boolean>)(Object) DEFAULT_SORT_POLICY) {
                @Override protected void invalidated() {
                    sort();
                }
            };
        }
        return sortPolicy;
    }


    // onSort
    
Called when there's a request to sort the control.
/**
     * Called when there's a request to sort the control.
     */
    private ObjectProperty<EventHandler<SortEvent<TreeTableView<S>>>> onSort;

    public void setOnSort(EventHandler<SortEvent<TreeTableView<S>>> value) {
        onSortProperty().set(value);
    }

    public EventHandler<SortEvent<TreeTableView<S>>> getOnSort() {
        if( onSort != null ) {
            return onSort.get();
        }
        return null;
    }

    public ObjectProperty<EventHandler<SortEvent<TreeTableView<S>>>> onSortProperty() {
        if( onSort == null ) {
            onSort = new ObjectPropertyBase<EventHandler<SortEvent<TreeTableView<S>>>>() {
                @Override protected void invalidated() {
                    EventType<SortEvent<TreeTableView<S>>> eventType = SortEvent.sortEvent();
                    EventHandler<SortEvent<TreeTableView<S>>> eventHandler = get();
                    setEventHandler(eventType, eventHandler);
                }

                @Override public Object getBean() {
                    return TreeTableView.this;
                }

                @Override public String getName() {
                    return "onSort";
                }
            };
        }
        return onSort;
    }



    /***************************************************************************
     *                                                                         *
     * Public API                                                              *
     *                                                                         *
     **************************************************************************/

    
{@inheritDoc} /** {@inheritDoc} */
    @Override protected void layoutChildren() {
        if (expandedItemCountDirty) {
            updateExpandedItemCount(getRoot());
        }

        super.layoutChildren();
    }

    
Scrolls the TreeTableView such that the item in the given index is visible to
the end user.
Params:
index – The index that should be made visible to the user, assuming
     of course that it is greater than, or equal to 0, and less than the
     number of the visible items in the TreeTableView./**
     * Scrolls the TreeTableView such that the item in the given index is visible to
     * the end user.
     *
     * @param index The index that should be made visible to the user, assuming
     *      of course that it is greater than, or equal to 0, and less than the
     *      number of the visible items in the TreeTableView.
     */
    public void scrollTo(int index) {
        ControlUtils.scrollToIndex(this, index);
    }

    
Called when there's a request to scroll an index into view using scrollTo(int) /**
     * Called when there's a request to scroll an index into view using {@link #scrollTo(int)}
     */
    private ObjectProperty<EventHandler<ScrollToEvent<Integer>>> onScrollTo;

    public void setOnScrollTo(EventHandler<ScrollToEvent<Integer>> value) {
        onScrollToProperty().set(value);
    }

    public EventHandler<ScrollToEvent<Integer>> getOnScrollTo() {
        if( onScrollTo != null ) {
            return onScrollTo.get();
        }
        return null;
    }

    public ObjectProperty<EventHandler<ScrollToEvent<Integer>>> onScrollToProperty() {
        if( onScrollTo == null ) {
            onScrollTo = new ObjectPropertyBase<EventHandler<ScrollToEvent<Integer>>>() {
                @Override protected void invalidated() {
                    setEventHandler(ScrollToEvent.scrollToTopIndex(), get());
                }

                @Override public Object getBean() {
                    return TreeTableView.this;
                }

                @Override public String getName() {
                    return "onScrollTo";
                }
            };
        }
        return onScrollTo;
    }

    
Scrolls the TreeTableView so that the given column is visible within the viewport.
Params:
column – The column that should be visible to the user./**
     * Scrolls the TreeTableView so that the given column is visible within the viewport.
     * @param column The column that should be visible to the user.
     */
    public void scrollToColumn(TreeTableColumn<S, ?> column) {
        ControlUtils.scrollToColumn(this, column);
    }

    
Scrolls the TreeTableView so that the given index is visible within the viewport.
Params:
columnIndex – The index of a column that should be visible to the user./**
     * Scrolls the TreeTableView so that the given index is visible within the viewport.
     * @param columnIndex The index of a column that should be visible to the user.
     */
    public void scrollToColumnIndex(int columnIndex) {
        if( getColumns() != null ) {
            ControlUtils.scrollToColumn(this, getColumns().get(columnIndex));
        }
    }

    
Called when there's a request to scroll a column into view using scrollToColumn(TreeTableColumn) or scrollToColumnIndex(int) /**
     * Called when there's a request to scroll a column into view using {@link #scrollToColumn(TreeTableColumn)}
     * or {@link #scrollToColumnIndex(int)}
     */
    private ObjectProperty<EventHandler<ScrollToEvent<TreeTableColumn<S, ?>>>> onScrollToColumn;

    public void setOnScrollToColumn(EventHandler<ScrollToEvent<TreeTableColumn<S, ?>>> value) {
        onScrollToColumnProperty().set(value);
    }

    public EventHandler<ScrollToEvent<TreeTableColumn<S, ?>>> getOnScrollToColumn() {
        if( onScrollToColumn != null ) {
            return onScrollToColumn.get();
        }
        return null;
    }

    public ObjectProperty<EventHandler<ScrollToEvent<TreeTableColumn<S, ?>>>> onScrollToColumnProperty() {
        if( onScrollToColumn == null ) {
            onScrollToColumn = new ObjectPropertyBase<EventHandler<ScrollToEvent<TreeTableColumn<S, ?>>>>() {
                @Override
                protected void invalidated() {
                    EventType<ScrollToEvent<TreeTableColumn<S, ?>>> type = ScrollToEvent.scrollToColumn();
                    setEventHandler(type, get());
                }
                @Override
                public Object getBean() {
                    return TreeTableView.this;
                }

                @Override
                public String getName() {
                    return "onScrollToColumn";
                }
            };
        }
        return onScrollToColumn;
    }

    
Returns the index position of the given TreeItem, assuming that it is
currently accessible through the tree hierarchy (most notably, that all
parent tree items are expanded). If a parent tree item is collapsed,
the result is that this method will return -1 to indicate that the
given tree item is not accessible in the tree.
Params:
item – The TreeItem for which the index is sought.
Returns:
An integer representing the location in the current TreeTableView of the
     first instance of the given TreeItem, or -1 if it is null or can not
     be found (for example, if a parent (all the way up to the root) is
     collapsed)./**
     * Returns the index position of the given TreeItem, assuming that it is
     * currently accessible through the tree hierarchy (most notably, that all
     * parent tree items are expanded). If a parent tree item is collapsed,
     * the result is that this method will return -1 to indicate that the
     * given tree item is not accessible in the tree.
     *
     * @param item The TreeItem for which the index is sought.
     * @return An integer representing the location in the current TreeTableView of the
     *      first instance of the given TreeItem, or -1 if it is null or can not
     *      be found (for example, if a parent (all the way up to the root) is
     *      collapsed).
     */
    public int getRow(TreeItem<S> item) {
        return TreeUtil.getRow(item, getRoot(), expandedItemCountDirty, isShowRoot());
    }

    
Returns the TreeItem in the given index, or null if it is out of bounds.
Params:
row – The index of the TreeItem being sought.
Returns:
The TreeItem in the given index, or null if it is out of bounds./**
     * Returns the TreeItem in the given index, or null if it is out of bounds.
     *
     * @param row The index of the TreeItem being sought.
     * @return The TreeItem in the given index, or null if it is out of bounds.
     */
    public TreeItem<S> getTreeItem(int row) {
        if (row < 0) return null;

        // normalize the requested row based on whether showRoot is set
        final int _row = isShowRoot() ? row : (row + 1);

        if (expandedItemCountDirty) {
            updateExpandedItemCount(getRoot());
        } else {
            if (treeItemCacheMap.containsKey(_row)) {
                SoftReference<TreeItem<S>> treeItemRef = treeItemCacheMap.get(_row);
                TreeItem<S> treeItem = treeItemRef.get();
                if (treeItem != null) {
                    return treeItem;
                }
            }
        }

        TreeItem<S> treeItem = TreeUtil.getItem(getRoot(), _row, expandedItemCountDirty);
        treeItemCacheMap.put(_row, new SoftReference<>(treeItem));
        return treeItem;
    }

    
Returns the number of levels of 'indentation' of the given TreeItem,
based on how many times getParent() can be recursively called. If the
given TreeItem is the root node of this TreeTableView, or if the TreeItem
does not have any parent set, the returned value will be zero. For each
time getParent() is recursively called, the returned value is incremented
by one.
Params:
node – The TreeItem for which the level is needed.
Returns:
An integer representing the number of parents above the given node,
        or -1 if the given TreeItem is null./**
     * Returns the number of levels of 'indentation' of the given TreeItem,
     * based on how many times getParent() can be recursively called. If the
     * given TreeItem is the root node of this TreeTableView, or if the TreeItem
     * does not have any parent set, the returned value will be zero. For each
     * time getParent() is recursively called, the returned value is incremented
     * by one.
     *
     * @param node The TreeItem for which the level is needed.
     * @return An integer representing the number of parents above the given node,
     *         or -1 if the given TreeItem is null.
     */
    public int getTreeItemLevel(TreeItem<?> node) {
        final TreeItem<?> root = getRoot();

        if (node == null) return -1;
        if (node == root) return 0;

        int level = 0;
        TreeItem<?> parent = node.getParent();
        while (parent != null) {
            level++;

            if (parent == root) {
                break;
            }

            parent = parent.getParent();
        }

        return level;
    }

    
The TreeTableColumns that are part of this TableView. As the user reorders
the TableView columns, this list will be updated to reflect the current
visual ordering.
Note: to display any data in a TableView, there must be at least one
TreeTableColumn in this ObservableList.
Returns:
the table table column/**
     * The TreeTableColumns that are part of this TableView. As the user reorders
     * the TableView columns, this list will be updated to reflect the current
     * visual ordering.
     *
     * <p>Note: to display any data in a TableView, there must be at least one
     * TreeTableColumn in this ObservableList.</p>
     * @return the table table column
     */
    public final ObservableList<TreeTableColumn<S,?>> getColumns() {
        return columns;
    }

    
The sortOrder list defines the order in which TreeTableColumn instances are sorted. An empty sortOrder list means that no sorting is being applied on the TableView. If the sortOrder list has one TreeTableColumn within it, the TableView will be sorted using the sortType and comparator properties of this TreeTableColumn (assuming TreeTableColumn.sortable is true). If the sortOrder list contains multiple TreeTableColumn instances, then the TableView is firstly sorted based on the properties of the first TreeTableColumn. If two elements are considered equal, then the second TreeTableColumn in the list is used to determine ordering. This repeats until the results from all TreeTableColumn comparators are considered, if necessary. 
Returns:
An ObservableList containing zero or more TreeTableColumn instances./**
     * The sortOrder list defines the order in which {@link TreeTableColumn} instances
     * are sorted. An empty sortOrder list means that no sorting is being applied
     * on the TableView. If the sortOrder list has one TreeTableColumn within it,
     * the TableView will be sorted using the
     * {@link TreeTableColumn#sortTypeProperty() sortType} and
     * {@link TreeTableColumn#comparatorProperty() comparator} properties of this
     * TreeTableColumn (assuming
     * {@link TreeTableColumn#sortableProperty() TreeTableColumn.sortable} is true).
     * If the sortOrder list contains multiple TreeTableColumn instances, then
     * the TableView is firstly sorted based on the properties of the first
     * TreeTableColumn. If two elements are considered equal, then the second
     * TreeTableColumn in the list is used to determine ordering. This repeats until
     * the results from all TreeTableColumn comparators are considered, if necessary.
     *
     * @return An ObservableList containing zero or more TreeTableColumn instances.
     */
    public final ObservableList<TreeTableColumn<S,?>> getSortOrder() {
        return sortOrder;
    }

    
Applies the currently installed resize policy against the given column,
resizing it based on the delta value provided.
Params:
column – the column
delta – the delta
Returns:
true if column resizing is applied/**
     * Applies the currently installed resize policy against the given column,
     * resizing it based on the delta value provided.
     * @param column the column
     * @param delta the delta
     * @return true if column resizing is applied
     */
    public boolean resizeColumn(TreeTableColumn<S,?> column, double delta) {
        if (column == null || Double.compare(delta, 0.0) == 0) return false;

        boolean allowed = getColumnResizePolicy().call(new TreeTableView.ResizeFeatures<S>(TreeTableView.this, column, delta));
        if (!allowed) return false;
        return true;
    }

    
Causes the cell at the given row/column view indexes to switch into
its editing state, if it is not already in it, and assuming that the
TableView and column are also editable.
Params:
row – the row
column – the column/**
     * Causes the cell at the given row/column view indexes to switch into
     * its editing state, if it is not already in it, and assuming that the
     * TableView and column are also editable.
     * @param row the row
     * @param column the column
     */
    public void edit(int row, TreeTableColumn<S,?> column) {
        if (!isEditable() || (column != null && ! column.isEditable())) {
            return;
        }

        if (row < 0 && column == null) {
            setEditingCell(null);
        } else {
            setEditingCell(new TreeTablePosition<>(this, row, column));
        }
    }

    
Returns an unmodifiable list containing the currently visible leaf columns.
Returns:
an unmodifiable list containing the currently visible leaf columns/**
     * Returns an unmodifiable list containing the currently visible leaf columns.
     * @return an unmodifiable list containing the currently visible leaf columns
     */
    public ObservableList<TreeTableColumn<S,?>> getVisibleLeafColumns() {
        return unmodifiableVisibleLeafColumns;
    }

    
Returns the position of the given column, relative to all other
visible leaf columns.
Params:
column – the column
Returns:
the position of the given column, relative to all other
visible leaf columns/**
     * Returns the position of the given column, relative to all other
     * visible leaf columns.
     * @param column the column
     * @return the position of the given column, relative to all other
     * visible leaf columns
     */
    public int getVisibleLeafIndex(TreeTableColumn<S,?> column) {
        return getVisibleLeafColumns().indexOf(column);
    }

    
Returns the TreeTableColumn in the given column index, relative to all other
visible leaf columns.
Params:
column – the column
Returns:
the TreeTableColumn in the given column index, relative to all other
visible leaf columns/**
     * Returns the TreeTableColumn in the given column index, relative to all other
     * visible leaf columns.
     * @param column the column
     * @return the TreeTableColumn in the given column index, relative to all other
     * visible leaf columns
     */
    public TreeTableColumn<S,?> getVisibleLeafColumn(int column) {
        if (column < 0 || column >= visibleLeafColumns.size()) return null;
        return visibleLeafColumns.get(column);
    }

    
The sort method forces the TreeTableView to re-run its sorting algorithm. More often than not it is not necessary to call this method directly, as it is automatically called when the sort order, sort policy, or the state of the TreeTableColumn sort type properties change. In other words, this method should only be called directly when something external changes and a sort is required. /**
     * The sort method forces the TreeTableView to re-run its sorting algorithm. More
     * often than not it is not necessary to call this method directly, as it is
     * automatically called when the {@link #getSortOrder() sort order},
     * {@link #sortPolicyProperty() sort policy}, or the state of the
     * TreeTableColumn {@link TreeTableColumn#sortTypeProperty() sort type} properties
     * change. In other words, this method should only be called directly when
     * something external changes and a sort is required.
     */
    public void sort() {
        final ObservableList<TreeTableColumn<S,?>> sortOrder = getSortOrder();

        // update the Comparator property
        final Comparator<TreeItem<S>> oldComparator = getComparator();
        setComparator(sortOrder.isEmpty() ? null : new TableColumnComparatorBase.TreeTableColumnComparator(sortOrder));

        // fire the onSort event and check if it is consumed, if
        // so, don't run the sort
        SortEvent<TreeTableView<S>> sortEvent = new SortEvent<>(TreeTableView.this, TreeTableView.this);
        fireEvent(sortEvent);
        if (sortEvent.isConsumed()) {
            // if the sort is consumed we could back out the last action (the code
            // is commented out right below), but we don't as we take it as a
            // sign that the developer has decided to handle the event themselves.

            // sortLock = true;
            // TableUtil.handleSortFailure(sortOrder, lastSortEventType, lastSortEventSupportInfo);
            // sortLock = false;
            return;
        }

        final List<TreeTablePosition<S,?>> prevState = new ArrayList<>(getSelectionModel().getSelectedCells());
        final int itemCount = prevState.size();

        // we set makeAtomic to true here, so that we don't fire intermediate
        // sort events - instead we send a single permutation event at the end
        // of this method.
        getSelectionModel().startAtomic();

        // get the sort policy and run it
        Callback<TreeTableView<S>, Boolean> sortPolicy = getSortPolicy();
        if (sortPolicy == null) return;
        Boolean success = sortPolicy.call(this);

        getSelectionModel().stopAtomic();

        if (success == null || ! success) {
            // the sort was a failure. Need to backout if possible
            sortLock = true;
            TableUtil.handleSortFailure(sortOrder, lastSortEventType, lastSortEventSupportInfo);
            setComparator(oldComparator);
            sortLock = false;
        } else {
            // sorting was a success, now we possibly fire an event on the
            // selection model that the items list has 'permutated' to a new ordering

            // FIXME we should support alternative selection model implementations!
            if (getSelectionModel() instanceof TreeTableViewArrayListSelectionModel) {
                final TreeTableViewArrayListSelectionModel<S> sm = (TreeTableViewArrayListSelectionModel<S>) getSelectionModel();
                final ObservableList<TreeTablePosition<S, ?>> newState = sm.getSelectedCells();

                List<TreeTablePosition<S, ?>> removed = new ArrayList<>();
                for (int i = 0; i < itemCount; i++) {
                    TreeTablePosition<S, ?> prevItem = prevState.get(i);
                    if (!newState.contains(prevItem)) {
                        removed.add(prevItem);
                    }
                }

                if (!removed.isEmpty()) {
                    // the sort operation effectively permutates the selectedCells list,
                    // but we cannot fire a permutation event as we are talking about
                    // TreeTablePosition's changing (which may reside in the same list
                    // position before and after the sort). Therefore, we need to fire
                    // a single add/remove event to cover the added and removed positions.
                    ListChangeListener.Change<TreeTablePosition<S, ?>> c = new NonIterableChange.GenericAddRemoveChange<>(0, itemCount, removed, newState);
                    sm.fireCustomSelectedCellsListChangeEvent(c);
                }
            }
        }
    }

    
Calling refresh() forces the TreeTableView control to recreate and repopulate the cells necessary to populate the visual bounds of the control. In other words, this forces the TreeTableView to update what it is showing to the user. This is useful in cases where the underlying data source has changed in a way that is not observed by the TreeTableView itself. 
Since:
JavaFX 8u60/**
     * Calling {@code refresh()} forces the TreeTableView control to recreate and
     * repopulate the cells necessary to populate the visual bounds of the control.
     * In other words, this forces the TreeTableView to update what it is showing to
     * the user. This is useful in cases where the underlying data source has
     * changed in a way that is not observed by the TreeTableView itself.
     *
     * @since JavaFX 8u60
     */
    public void refresh() {
        getProperties().put(Properties.RECREATE, Boolean.TRUE);
    }



    
                                                                        *
Private Implementation                                                  *
                                                                        *
/***************************************************************************
     *                                                                         *
     * Private Implementation                                                  *
     *                                                                         *
     **************************************************************************/

    private boolean sortLock = false;
    private TableUtil.SortEventType lastSortEventType = null;
    private Object[] lastSortEventSupportInfo = null;

    private void doSort(final TableUtil.SortEventType sortEventType, final Object... supportInfo) {
        if (sortLock) {
            return;
        }

        this.lastSortEventType = sortEventType;
        this.lastSortEventSupportInfo = supportInfo;
        sort();
        this.lastSortEventType = null;
        this.lastSortEventSupportInfo = null;
    }

    private void updateExpandedItemCount(TreeItem<S> treeItem) {
        setExpandedItemCount(TreeUtil.updateExpandedItemCount(treeItem, expandedItemCountDirty, isShowRoot()));

        if (expandedItemCountDirty) {
            // this is a very inefficient thing to do, but for now having a cache
            // is better than nothing at all...
            treeItemCacheMap.clear();
        }

        expandedItemCountDirty = false;
    }

    private void updateRootExpanded() {
        // if we aren't showing the root, and the root isn't expanded, we expand
        // it now so that something is shown.
        if (!isShowRoot() && getRoot() != null && ! getRoot().isExpanded()) {
            getRoot().setExpanded(true);
        }
    }


    // --- Content width
    private void setContentWidth(double contentWidth) {
        this.contentWidth = contentWidth;
        if (isInited) {
            // sometimes the current column resize policy will have to modify the
            // column width of all columns in the table if the table width changes,
            // so we short-circuit the resize function and just go straight there
            // with a null TreeTableColumn, which indicates to the resize policy function
            // that it shouldn't actually do anything specific to one column.
            getColumnResizePolicy().call(new TreeTableView.ResizeFeatures<S>(TreeTableView.this, null, 0.0));
        }
    }

    
Recomputes the currently visible leaf columns in this TableView.
/**
     * Recomputes the currently visible leaf columns in this TableView.
     */
    private void updateVisibleLeafColumns() {
        // update visible leaf columns list
        List<TreeTableColumn<S,?>> cols = new ArrayList<TreeTableColumn<S,?>>();
        buildVisibleLeafColumns(getColumns(), cols);
        visibleLeafColumns.setAll(cols);

        // sometimes the current column resize policy will have to modify the
        // column width of all columns in the table if the table width changes,
        // so we short-circuit the resize function and just go straight there
        // with a null TreeTableColumn, which indicates to the resize policy function
        // that it shouldn't actually do anything specific to one column.
        getColumnResizePolicy().call(new TreeTableView.ResizeFeatures<S>(TreeTableView.this, null, 0.0));
    }

    private void buildVisibleLeafColumns(List<TreeTableColumn<S,?>> cols, List<TreeTableColumn<S,?>> vlc) {
        for (TreeTableColumn<S,?> c : cols) {
            if (c == null) continue;

            boolean hasChildren = ! c.getColumns().isEmpty();

            if (hasChildren) {
                buildVisibleLeafColumns(c.getColumns(), vlc);
            } else if (c.isVisible()) {
                vlc.add(c);
            }
        }
    }



    
                                                                        *
Stylesheet Handling                                                     *
                                                                        *
/***************************************************************************
     *                                                                         *
     * Stylesheet Handling                                                     *
     *                                                                         *
     **************************************************************************/

    private static final String DEFAULT_STYLE_CLASS = "tree-table-view";

    private static final PseudoClass PSEUDO_CLASS_CELL_SELECTION =
            PseudoClass.getPseudoClass("cell-selection");
    private static final PseudoClass PSEUDO_CLASS_ROW_SELECTION =
            PseudoClass.getPseudoClass("row-selection");

    private static class StyleableProperties {
        private static final CssMetaData<TreeTableView<?>,Number> FIXED_CELL_SIZE =
                new CssMetaData<TreeTableView<?>,Number>("-fx-fixed-cell-size",
                                                     SizeConverter.getInstance(),
                                                     Region.USE_COMPUTED_SIZE) {

                    @Override public Double getInitialValue(TreeTableView<?> node) {
                        return node.getFixedCellSize();
                    }

                    @Override public boolean isSettable(TreeTableView<?> n) {
                        return n.fixedCellSize == null || !n.fixedCellSize.isBound();
                    }

                    @Override public StyleableProperty<Number> getStyleableProperty(TreeTableView<?> n) {
                        return (StyleableProperty<Number>)(WritableValue<Number>) n.fixedCellSizeProperty();
                    }
                };

        private static final List<CssMetaData<? extends Styleable, ?>> STYLEABLES;
        static {
            final List<CssMetaData<? extends Styleable, ?>> styleables =
                    new ArrayList<CssMetaData<? extends Styleable, ?>>(Control.getClassCssMetaData());
            styleables.add(FIXED_CELL_SIZE);
            STYLEABLES = Collections.unmodifiableList(styleables);
        }
    }

    
Returns:
The CssMetaData associated with this class, which may include the
CssMetaData of its superclasses./**
     * @return The CssMetaData associated with this class, which may include the
     * CssMetaData of its superclasses.
     */
    public static List<CssMetaData<? extends Styleable, ?>> getClassCssMetaData() {
        return StyleableProperties.STYLEABLES;
    }

    
{@inheritDoc}
Since:
JavaFX 8.0/**
     * {@inheritDoc}
     * @since JavaFX 8.0
     */
    @Override
    public List<CssMetaData<? extends Styleable, ?>> getControlCssMetaData() {
        return getClassCssMetaData();
    }

    
{@inheritDoc} /** {@inheritDoc} */
    @Override protected Skin<?> createDefaultSkin() {
        return new TreeTableViewSkin<S>(this);
    }



    /***************************************************************************
     *                                                                         *
     * Accessibility handling                                                  *
     *                                                                         *
     **************************************************************************/

    
{@inheritDoc} /** {@inheritDoc} */
    @Override
    public Object queryAccessibleAttribute(AccessibleAttribute attribute, Object... parameters) {
        switch (attribute) {
            case ROW_COUNT: return getExpandedItemCount();
            case COLUMN_COUNT: return getVisibleLeafColumns().size();

            /*
             * TreeTableViewSkin returns TreeTableRows back to TreeTableView.
             * TreeTableRowSkin returns TreeTableCells back to TreeTableRow.
             */
            case SELECTED_ITEMS: {
                @SuppressWarnings("unchecked")
                ObservableList<TreeTableRow<S>> rows = (ObservableList<TreeTableRow<S>>)super.queryAccessibleAttribute(attribute, parameters);
                List<Node> selection = new ArrayList<>();
                for (TreeTableRow<S> row : rows) {
                    @SuppressWarnings("unchecked")
                    ObservableList<Node> cells = (ObservableList<Node>)row.queryAccessibleAttribute(attribute, parameters);
                    if (cells != null) selection.addAll(cells);
                }
                return FXCollections.observableArrayList(selection);
            }
            case FOCUS_ITEM: {
                Node row = (Node)super.queryAccessibleAttribute(attribute, parameters);
                if (row == null) return null;
                Node cell = (Node)row.queryAccessibleAttribute(attribute, parameters);
                /* cell equals to null means the row is a placeholder node */
                return cell != null ?  cell : row;
            }
            case CELL_AT_ROW_COLUMN: {
                @SuppressWarnings("unchecked")
                TreeTableRow<S> row = (TreeTableRow<S>)super.queryAccessibleAttribute(attribute, parameters);
                return row != null ? row.queryAccessibleAttribute(attribute, parameters) : null;
            }
            case MULTIPLE_SELECTION: {
                TreeTableViewSelectionModel<S> sm = getSelectionModel();
                return sm != null && sm.getSelectionMode() == SelectionMode.MULTIPLE;
            }
            default: return super.queryAccessibleAttribute(attribute, parameters);
        }
    }

    /***************************************************************************
     *                                                                         *
     * Support Classes                                                         *
     *                                                                         *
     **************************************************************************/

     
An immutable wrapper class for use in the TableView column resize functionality. 
Since:
JavaFX 8.0/**
      * An immutable wrapper class for use in the TableView
     * {@link TreeTableView#columnResizePolicyProperty() column resize} functionality.
      * @since JavaFX 8.0
      */
     public static class ResizeFeatures<S> extends ResizeFeaturesBase<TreeItem<S>> {
        private TreeTableView<S> treeTable;

        
Creates an instance of this class, with the provided TreeTableView,
TreeTableColumn and delta values being set and stored in this immutable
instance.
Params:
treeTable – The TreeTableView upon which the resize operation is occurring.
column – The column upon which the resize is occurring, or null
     if this ResizeFeatures instance is being created as a result of a
     TreeTableView resize operation.
delta – The amount of horizontal space added or removed in the
     resize operation./**
         * Creates an instance of this class, with the provided TreeTableView,
         * TreeTableColumn and delta values being set and stored in this immutable
         * instance.
         *
         * @param treeTable The TreeTableView upon which the resize operation is occurring.
         * @param column The column upon which the resize is occurring, or null
         *      if this ResizeFeatures instance is being created as a result of a
         *      TreeTableView resize operation.
         * @param delta The amount of horizontal space added or removed in the
         *      resize operation.
         */
        public ResizeFeatures(TreeTableView<S> treeTable, TreeTableColumn<S,?> column, Double delta) {
            super(column, delta);
            this.treeTable = treeTable;
        }

        
Returns the column upon which the resize is occurring, or null
if this ResizeFeatures instance was created as a result of a
TreeTableView resize operation.
/**
         * Returns the column upon which the resize is occurring, or null
         * if this ResizeFeatures instance was created as a result of a
         * TreeTableView resize operation.
         */
        @Override public TreeTableColumn<S,?> getColumn() {
            return (TreeTableColumn<S,?>) super.getColumn();
        }

        
Returns the TreeTableView upon which the resize operation is occurring.
Returns:
the TreeTableView upon which the resize operation is occurring/**
         * Returns the TreeTableView upon which the resize operation is occurring.
         * @return the TreeTableView upon which the resize operation is occurring
         */
        public TreeTableView<S> getTable() { return treeTable; }
    }



    
An Event subclass used specifically in TreeTableView for representing edit-related events. It provides additional API to easily access the TreeItem that the edit event took place on, as well as the input provided by the end user. 
Type parameters:
<S> – The type of the input, which is the same type as the TreeTableView
     itself.
Since:
JavaFX 8.0/**
     * An {@link Event} subclass used specifically in TreeTableView for representing
     * edit-related events. It provides additional API to easily access the
     * TreeItem that the edit event took place on, as well as the input provided
     * by the end user.
     *
     * @param <S> The type of the input, which is the same type as the TreeTableView
     *      itself.
     * @since JavaFX 8.0
     */
    public static class EditEvent<S> extends Event {
        private static final long serialVersionUID = -4437033058917528976L;

        
Common supertype for all edit event types.
/**
         * Common supertype for all edit event types.
         */
        public static final EventType<?> ANY = EDIT_ANY_EVENT;

        private final TreeTableView<S> source;
        private final S oldValue;
        private final S newValue;
        private transient final TreeItem<S> treeItem;

        
Creates a new EditEvent instance to represent an edit event. This event is used for TreeTableView.editStartEvent(), TreeTableView.editCommitEvent() and TreeTableView.editCancelEvent() types. 
Params:
source – the source
eventType – the eventType
treeItem – the treeItem
oldValue – the oldValue
newValue – the newValue/**
         * Creates a new EditEvent instance to represent an edit event. This
         * event is used for {@link #editStartEvent()},
         * {@link #editCommitEvent()} and {@link #editCancelEvent()} types.
         * @param source the source
         * @param eventType the eventType
         * @param treeItem the treeItem
         * @param oldValue the oldValue
         * @param newValue the newValue
         */
        public EditEvent(TreeTableView<S> source,
                         EventType<? extends TreeTableView.EditEvent> eventType,
                         TreeItem<S> treeItem, S oldValue, S newValue) {
            super(source, Event.NULL_SOURCE_TARGET, eventType);
            this.source = source;
            this.oldValue = oldValue;
            this.newValue = newValue;
            this.treeItem = treeItem;
        }

        
Returns the TreeTableView upon which the edit took place.
Returns:
the TreeTableView upon which the edit took place/**
         * Returns the TreeTableView upon which the edit took place.
         * @return the TreeTableView upon which the edit took place
         */
        @Override public TreeTableView<S> getSource() {
            return source;
        }

        
Returns the TreeItem upon which the edit took place. 
Returns:
the TreeItem upon which the edit took place/**
         * Returns the {@link TreeItem} upon which the edit took place.
         * @return the {@link TreeItem} upon which the edit took place
         */
        public TreeItem<S> getTreeItem() {
            return treeItem;
        }

        
Returns the new value input into the TreeItem by the end user.
Returns:
the new value input into the TreeItem by the end user/**
         * Returns the new value input into the TreeItem by the end user.
         * @return the new value input into the TreeItem by the end user
         */
        public S getNewValue() {
            return newValue;
        }

        
Returns the old value that existed in the TreeItem prior to the current
edit event.
Returns:
the old value that existed in the TreeItem prior to the current
edit event/**
         * Returns the old value that existed in the TreeItem prior to the current
         * edit event.
         * @return the old value that existed in the TreeItem prior to the current
         * edit event
         */
        public S getOldValue() {
            return oldValue;
        }
    }



     
A simple extension of the SelectionModel abstract class to allow for special support for TreeTableView controls. 
Since:
JavaFX 8.0/**
     * A simple extension of the {@link SelectionModel} abstract class to
     * allow for special support for TreeTableView controls.
      *
     * @since JavaFX 8.0
     */
    public static abstract class TreeTableViewSelectionModel<S> extends
            TableSelectionModel<TreeItem<S>> {

        
                                                                    *
Private fields                                                      *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Private fields                                                      *
         *                                                                     *
         **********************************************************************/

        private final TreeTableView<S> treeTableView;


        /***********************************************************************
         *                                                                     *
         * Constructors                                                        *
         *                                                                     *
         **********************************************************************/

        
Builds a default TreeTableViewSelectionModel instance with the provided
TreeTableView.
Params:
treeTableView – The TreeTableView upon which this selection model should
     operate.
Throws:
NullPointerException – TreeTableView can not be null./**
         * Builds a default TreeTableViewSelectionModel instance with the provided
         * TreeTableView.
         * @param treeTableView The TreeTableView upon which this selection model should
         *      operate.
         * @throws NullPointerException TreeTableView can not be null.
         */
        public TreeTableViewSelectionModel(final TreeTableView<S> treeTableView) {
            if (treeTableView == null) {
                throw new NullPointerException("TreeTableView can not be null");
            }

            this.treeTableView = treeTableView;
        }



        /***********************************************************************
         *                                                                     *
         * Abstract API                                                        *
         *                                                                     *
         **********************************************************************/

         
A read-only ObservableList representing the currently selected cells
in this TreeTableView. Rather than directly modify this list, please
use the other methods provided in the TreeTableViewSelectionModel.
Returns:
a list of selected cells/**
         * A read-only ObservableList representing the currently selected cells
         * in this TreeTableView. Rather than directly modify this list, please
         * use the other methods provided in the TreeTableViewSelectionModel.
         * @return a list of selected cells
         */
        public abstract ObservableList<TreeTablePosition<S,?>> getSelectedCells();



        /***********************************************************************
         *                                                                     *
         * Public API                                                          *
         *                                                                     *
         **********************************************************************/

         
Returns the TreeTableView instance that this selection model is installed in.
Returns:
the TreeTableView instance that this selection model is installed in/**
          * Returns the TreeTableView instance that this selection model is installed in.
         * @return the TreeTableView instance that this selection model is installed in
          */
         public TreeTableView<S> getTreeTableView() {
             return treeTableView;
         }

         
{@inheritDoc} /** {@inheritDoc} */
         @Override public TreeItem<S> getModelItem(int index) {
             return treeTableView.getTreeItem(index);
         }

         
{@inheritDoc} /** {@inheritDoc} */
         @Override protected int getItemCount() {
             return treeTableView.getExpandedItemCount();
         }

         
{@inheritDoc} /** {@inheritDoc} */
         @Override public void focus(int row) {
             focus(row, null);
         }

         
{@inheritDoc} /** {@inheritDoc} */
         @Override public int getFocusedIndex() {
             return getFocusedCell().getRow();
         }

         
{@inheritDoc} /** {@inheritDoc} */
         @Override public void selectRange(int minRow, TableColumnBase<TreeItem<S>,?> minColumn,
                                           int maxRow, TableColumnBase<TreeItem<S>,?> maxColumn) {
             final int minColumnIndex = treeTableView.getVisibleLeafIndex((TreeTableColumn<S,?>)minColumn);
             final int maxColumnIndex = treeTableView.getVisibleLeafIndex((TreeTableColumn<S,?>)maxColumn);
             for (int _row = minRow; _row <= maxRow; _row++) {
                 for (int _col = minColumnIndex; _col <= maxColumnIndex; _col++) {
                     select(_row, treeTableView.getVisibleLeafColumn(_col));
                 }
             }
         }



        
                                                                    *
Private implementation                                              *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Private implementation                                              *
         *                                                                     *
         **********************************************************************/

         private void focus(int row, TreeTableColumn<S,?> column) {
             focus(new TreeTablePosition<>(getTreeTableView(), row, column));
         }

         private void focus(TreeTablePosition<S,?> pos) {
             if (getTreeTableView().getFocusModel() == null) return;

             getTreeTableView().getFocusModel().focus(pos.getRow(), pos.getTableColumn());
         }

         private TreeTablePosition<S,?> getFocusedCell() {
             if (treeTableView.getFocusModel() == null) {
                 return new TreeTablePosition<>(treeTableView, -1, null);
             }
             return treeTableView.getFocusModel().getFocusedCell();
         }
     }



    
A primitive selection model implementation, using a List to store all
selected indices.
/**
     * A primitive selection model implementation, using a List<Integer> to store all
     * selected indices.
     */
    // package for testing
    static class TreeTableViewArrayListSelectionModel<S> extends TreeTableViewSelectionModel<S> {

        private final MappingChange.Map<TreeTablePosition<S,?>,Integer> cellToIndicesMap = f -> f.getRow();

        private TreeTableView<S> treeTableView = null;

        
                                                                    *
Constructors                                                        *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Constructors                                                        *
         *                                                                     *
         **********************************************************************/

        public TreeTableViewArrayListSelectionModel(final TreeTableView<S> treeTableView) {
            super(treeTableView);
            this.treeTableView = treeTableView;

            this.treeTableView.rootProperty().addListener(weakRootPropertyListener);
            this.treeTableView.showRootProperty().addListener(showRootPropertyListener);
            updateTreeEventListener(null, treeTableView.getRoot());

            selectedCellsMap = new SelectedCellsMap<TreeTablePosition<S,?>>(this::fireCustomSelectedCellsListChangeEvent) {
                @Override public boolean isCellSelectionEnabled() {
                    return TreeTableViewArrayListSelectionModel.this.isCellSelectionEnabled();
                }
            };

            selectedCellsSeq = new ReadOnlyUnbackedObservableList<TreeTablePosition<S,?>>() {
                @Override public TreeTablePosition<S,?> get(int i) {
                    return selectedCellsMap.get(i);
                }

                @Override public int size() {
                    return selectedCellsMap.size();
                }
            };
//            selectedCellsSeq.addListener((ListChangeListener<? super TreeTablePosition<S,?>>) c -> {
//                ControlUtils.updateSelectedIndices(this, c);
//            });

            updateDefaultSelection();

            cellSelectionEnabledProperty().addListener(o -> {
                updateDefaultSelection();
                TableCellBehaviorBase.setAnchor(treeTableView, getFocusedCell(), true);
            });
        }

        private void dispose() {
            this.treeTableView.rootProperty().removeListener(weakRootPropertyListener);
            this.treeTableView.showRootProperty().removeListener(showRootPropertyListener);

            TreeItem<S> root = this.treeTableView.getRoot();
            if (root != null) {
                root.removeEventHandler(TreeItem.<S>expandedItemCountChangeEvent(), weakTreeItemListener);
            }
        }

        private void updateTreeEventListener(TreeItem<S> oldRoot, TreeItem<S> newRoot) {
            if (oldRoot != null && weakTreeItemListener != null) {
                oldRoot.removeEventHandler(TreeItem.<S>expandedItemCountChangeEvent(), weakTreeItemListener);
            }

            if (newRoot != null) {
                weakTreeItemListener = new WeakEventHandler<>(treeItemListener);
                newRoot.addEventHandler(TreeItem.<S>expandedItemCountChangeEvent(), weakTreeItemListener);
            }
        }

        private ChangeListener<TreeItem<S>> rootPropertyListener = (observable, oldValue, newValue) -> {
            updateDefaultSelection();

            updateTreeEventListener(oldValue, newValue);
        };

        private InvalidationListener showRootPropertyListener = o -> {
            shiftSelection(0, treeTableView.isShowRoot() ? 1 : -1, null);
        };

        private EventHandler<TreeItem.TreeModificationEvent<S>> treeItemListener = new EventHandler<>() {
            @Override public void handle(TreeItem.TreeModificationEvent<S> e) {

                if (getSelectedIndex() == -1 && getSelectedItem() == null) return;

                final TreeItem<S> treeItem = e.getTreeItem();
                if (treeItem == null) return;

                final int oldSelectedIndex = getSelectedIndex();

                treeTableView.expandedItemCountDirty = true;

                // we only shift selection from this row - everything before it
                // is safe. We might change this below based on certain criteria
                int startRow = treeTableView.getRow(treeItem);

                int shift = 0;
                ListChangeListener.Change<? extends TreeItem<?>> change = e.getChange();
                if (change != null) {
                    change.next();
                }

                do {
                    final int addedSize = change == null ? 0 : change.getAddedSize();
                    final int removedSize = change == null ? 0 : change.getRemovedSize();

                    if (e.wasExpanded()) {
                        // need to shuffle selection by the number of visible children
                        shift += treeItem.getExpandedDescendentCount(false) - 1;
                        startRow++;
                    } else if (e.wasCollapsed()) {
                        // remove selection from any child treeItem, and also determine
                        // if any child item was selected (in which case the parent
                        // takes the selection on collapse)
                        treeItem.getExpandedDescendentCount(false);
                        final int count = treeItem.previousExpandedDescendentCount;

                        final int selectedIndex = getSelectedIndex();
                        final boolean wasPrimarySelectionInChild =
                                selectedIndex >= (startRow + 1) &&
                                        selectedIndex < (startRow + count);

                        boolean wasAnyChildSelected = false;
                        final boolean isCellSelectionMode = isCellSelectionEnabled();
                        ObservableList<TreeTableColumn<S, ?>> columns = getTreeTableView().getVisibleLeafColumns();

                        selectedIndices._beginChange();
                        final int from = startRow + 1;
                        final int to = startRow + count;
                        final List<Integer> removed = new ArrayList<>();
                        TreeTableColumn<S, ?> selectedColumn = null;
                        for (int i = from; i < to; i++) {
                            // we have to handle cell selection mode differently than
                            // row selection mode. Refer to RT-34103 for the bug report
                            // that drove this change, but in short the issue was that
                            // when collapsing a branch that had selection, we were
                            // always calling isSelected(row), but that always returns
                            // false in cell selection mode.
                            if (isCellSelectionMode) {
                                for (int column = 0; column < columns.size(); column++) {
                                    final TreeTableColumn<S, ?> col = columns.get(column);
                                    if (isSelected(i, col)) {
                                        wasAnyChildSelected = true;
                                        clearSelection(i, col);
                                        selectedColumn = col;
                                    }
                                }
                            } else {
                                if (isSelected(i)) {
                                    wasAnyChildSelected = true;
                                    removed.add(i);
                                }
                            }
                        }

                        ControlUtils.reducingChange(selectedIndices, removed);

                        for (int index : removed) {
                            startAtomic();
                            // we pass in false here to prevent a lookup into the TreeItem, as it is unnecessary
                            // and results in JDK-8152396
                            clearSelection(new TreeTablePosition<>(treeTableView, index, null, false));
                            stopAtomic();
                        }
                        selectedIndices._endChange();

                        // put selection onto the newly-collapsed tree item
                        if (wasPrimarySelectionInChild && wasAnyChildSelected) {
                            select(startRow, selectedColumn);
                        }

                        shift += -count + 1;
                        startRow++;
                    } else if (e.wasPermutated()) {
                        // General approach:
                        //   -- detected a sort has happened
                        //   -- Create a permutation lookup map (1)
                        //   -- dump all the selected indices into a list (2)
                        //   -- create a list containing the new indices (3)
                        //   -- for each previously-selected index (4)
                        //     -- if index is in the permutation lookup map
                        //       -- add the new index to the new indices list
                        //   -- Perform batch selection (5)

                        startAtomic();

                        final int offset = startRow + 1;

                        // (1)
                        int length = e.getTo() - e.getFrom();
                        HashMap<Integer, Integer> pMap = new HashMap<> (length);
                        for (int i = e.getFrom(); i < e.getTo(); i++) {
                            pMap.put(i, e.getChange().getPermutation(i));
                        }

                        // (2)
                        List<TreeTablePosition<S,?>> selectedIndices = new ArrayList<>(getSelectedCells());

                        // (3)
                        List<TreeTablePosition<S,?>> newIndices = new ArrayList<>(selectedIndices.size());

                        // (4)
                        boolean selectionIndicesChanged = false;
                        for (int i = 0; i < selectedIndices.size(); i++) {
                            final TreeTablePosition<S,?> oldIndex = selectedIndices.get(i);
                            final int oldRow = oldIndex.getRow() - offset;

                            if (pMap.containsKey(oldRow)) {
                                int newIndex = pMap.get(oldRow) + offset;

                                selectionIndicesChanged = selectionIndicesChanged || newIndex != oldRow;

                                newIndices.add(new TreeTablePosition<>(oldIndex.getTreeTableView(), newIndex, oldIndex.getTableColumn()));
                            }

                            // check if the root element of this event was selected, so that we can retain it
                            if (oldIndex.getRow() == startRow) {
                                newIndices.add(new TreeTablePosition<>(oldIndex.getTreeTableView(), oldIndex.getRow(), oldIndex.getTableColumn()));
                            }
                        }

                        if (selectionIndicesChanged) {
                            // (5)
                            quietClearSelection();
                            stopAtomic();

                            selectedCellsMap.setAll(newIndices);

                            final int offsetOldIndex = oldSelectedIndex - offset;
                            if (offsetOldIndex >= 0 && offsetOldIndex < getItemCount()) {
                                int newIndex = e.getChange().getPermutation(offsetOldIndex);
                                setSelectedIndex(newIndex + offset);
                                focus(newIndex + offset);
                            }
                        } else {
                            stopAtomic();
                        }
                    } else if (e.wasAdded()) {
                        // shuffle selection by the number of added items
                        shift += treeItem.isExpanded() ? addedSize : 0;

                        // RT-32963: We were taking the startRow from the TreeItem
                        // in which the children were added, rather than from the
                        // actual position of the new child. This led to selection
                        // being moved off the parent TreeItem by mistake.
                        // The 'if (e.getAddedSize() == 1)' condition here was
                        // subsequently commented out due to RT-33894.
                        startRow = treeTableView.getRow(e.getChange().getAddedSubList().get(0));

                        TreeTablePosition<S, ?> anchor = TreeTableCellBehavior.getAnchor(treeTableView, null);
                        if (anchor != null) {
                            boolean isAnchorSelected = isSelected(anchor.getRow(), anchor.getTableColumn());
                            if (isAnchorSelected) {
                                TreeTablePosition<S, ?> newAnchor = new TreeTablePosition<>(treeTableView, anchor.getRow() + shift, anchor.getTableColumn());
                                TreeTableCellBehavior.setAnchor(treeTableView, newAnchor, false);
                            }
                        }
                    } else if (e.wasRemoved()) {
                        // shuffle selection by the number of removed items
                        shift += treeItem.isExpanded() ? -removedSize : 0;

                        // the start row is incorrect - it is _not_ the index of the
                        // TreeItem in which the children were removed from (which is
                        // what it currently represents). We need to take the 'from'
                        // value out of the event and make use of that to understand
                        // what actually changed inside the children list.
                        startRow += e.getFrom() + 1;

                        // whilst we are here, we should check if the removed items
                        // are part of the selectedItems list - and remove them
                        // from selection if they are (as per RT-15446)
                        final List<Integer> selectedIndices = getSelectedIndices();
                        final List<TreeItem<S>> selectedItems = getSelectedItems();
                        final TreeItem<S> selectedItem = getSelectedItem();
                        final List<? extends TreeItem<S>> removedChildren = e.getChange().getRemoved();

                        for (int i = 0; i < selectedIndices.size() && !selectedItems.isEmpty(); i++) {
                            int index = selectedIndices.get(i);
                            if (index > selectedItems.size()) break;

                            if (removedChildren.size() == 1 &&
                                    selectedItems.size() == 1 &&
                                    selectedItem != null &&
                                    selectedItem.equals(removedChildren.get(0))) {
                                // Bug fix for RT-28637
                                if (oldSelectedIndex < getItemCount()) {
                                    final int previousRow = oldSelectedIndex == 0 ? 0 : oldSelectedIndex - 1;
                                    TreeItem<S> newSelectedItem = getModelItem(previousRow);
                                    if (!selectedItem.equals(newSelectedItem)) {
                                        clearAndSelect(previousRow);
                                    }
                                }
                            }
                        }
                    }
                } while (e.getChange() != null && e.getChange().next());

                shiftSelection(startRow, shift, new Callback<ShiftParams, Void>() {
                    @Override public Void call(ShiftParams param) {

                        // we make the shifts atomic, as otherwise listeners to
                        // the items / indices lists get a lot of intermediate
                        // noise. They eventually get the summary event fired
                        // from within shiftSelection, so this is ok.
                        startAtomic();

                        final int clearIndex = param.getClearIndex();
                        final int setIndex = param.getSetIndex();
                        TreeTablePosition<S,?> oldTP = null;
                        if (clearIndex > -1) {
                            for (int i = 0; i < selectedCellsMap.size(); i++) {
                                TreeTablePosition<S,?> tp = selectedCellsMap.get(i);
                                if (tp.getRow() == clearIndex) {
                                    oldTP = tp;
                                    selectedCellsMap.remove(tp);
                                } else if (tp.getRow() == setIndex && !param.isSelected()) {
                                    selectedCellsMap.remove(tp);
                                }
                            }
                        }

                        if (oldTP != null && param.isSelected()) {
                            TreeTablePosition<S,?> newTP = new TreeTablePosition<>(
                                    treeTableView, param.getSetIndex(), oldTP.getTableColumn());

                            selectedCellsMap.add(newTP);
                        }

                        stopAtomic();

                        return null;
                    }
                });
            }
        };

        private WeakChangeListener<TreeItem<S>> weakRootPropertyListener =
                new WeakChangeListener<>(rootPropertyListener);

        private WeakEventHandler<TreeItem.TreeModificationEvent<S>> weakTreeItemListener;



        
                                                                    *
Observable properties (and getters/setters)                         *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Observable properties (and getters/setters)                         *
         *                                                                     *
         **********************************************************************/

        // the only 'proper' internal data structure, selectedItems and selectedIndices
        // are both 'read-only and unbacked'.
        private final SelectedCellsMap<TreeTablePosition<S,?>> selectedCellsMap;

        private final ReadOnlyUnbackedObservableList<TreeTablePosition<S,?>> selectedCellsSeq;
        @Override public ObservableList<TreeTablePosition<S,?>> getSelectedCells() {
            return selectedCellsSeq;
        }


        /***********************************************************************
         *                                                                     *
         * Internal properties                                                 *
         *                                                                     *
         **********************************************************************/



        
                                                                    *
Public selection API                                                *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Public selection API                                                *
         *                                                                     *
         **********************************************************************/

        @Override public void clearAndSelect(int row) {
            clearAndSelect(row, null);
        }

        @Override public void clearAndSelect(int row, TableColumnBase<TreeItem<S>,?> column) {
            if (row < 0 || row >= getItemCount()) return;

            final TreeTablePosition<S,?> newTablePosition = new TreeTablePosition<>(getTreeTableView(), row, (TreeTableColumn<S,?>)column);
            final boolean isCellSelectionEnabled = isCellSelectionEnabled();

            // replace the anchor
            TreeTableCellBehavior.setAnchor(treeTableView, newTablePosition, false);

            // firstly we make a copy of the selection, so that we can send out
            // the correct details in the selection change event.
            List<TreeTablePosition<S,?>> previousSelection = new ArrayList<>(selectedCellsMap.getSelectedCells());

            // secondly we check if we can short-circuit out of here because the new selection
            // equals the current selection
            final boolean wasSelected = isSelected(row, column);
            if (wasSelected && previousSelection.size() == 1) {
                // before we return, we double-check that the selected item
                // is equal to the item in the given index
                TreeTablePosition<S,?> selectedCell = getSelectedCells().get(0);
                if (getSelectedItem() == getModelItem(row)) {
                    if (selectedCell.getRow() == row && selectedCell.getTableColumn() == column) {
                        return;
                    }
                }
            }

            // RT-32411: We used to call quietClearSelection() here, but this
            // resulted in the selectedItems and selectedIndices lists never
            // reporting that they were empty.
            // makeAtomic toggle added to resolve RT-32618
            startAtomic();

            // then clear the current selection
            clearSelection();

            // and select the new cell
            select(row, column);

            stopAtomic();

            // We remove the new selection from the list seeing as it is not removed.
            if (isCellSelectionEnabled) {
                previousSelection.remove(newTablePosition);
            } else {
                for (TreeTablePosition<S,?> tp : previousSelection) {
                    if (tp.getRow() == row) {
                        previousSelection.remove(tp);
                        break;
                    }
                }
            }

            // fire off a single add/remove/replace notification (rather than
            // individual remove and add notifications) - see RT-33324
            ListChangeListener.Change<TreeTablePosition<S, ?>> change;

            /*
             * getFrom() documentation:
             *   If wasAdded is true, the interval contains all the values that were added.
             *   If wasPermutated is true, the interval marks the values that were permutated.
             *   If wasRemoved is true and wasAdded is false, getFrom() and getTo() should
             *   return the same number - the place where the removed elements were positioned in the list.
             */
            if (wasSelected) {
                change = ControlUtils.buildClearAndSelectChange(selectedCellsSeq, previousSelection, row);
            } else {
                final int changeIndex = isCellSelectionEnabled ? 0 : Math.max(0, selectedCellsSeq.indexOf(newTablePosition));
                final int changeSize = isCellSelectionEnabled ? getSelectedCells().size() : 1;
                change = new NonIterableChange.GenericAddRemoveChange<>(
                        changeIndex, changeIndex + changeSize, previousSelection, selectedCellsSeq);
//                selectedCellsSeq._beginChange();
//                selectedCellsSeq._nextAdd(changeIndex, changeIndex + changeSize);
//                selectedCellsSeq._nextRemove(changeIndex, previousSelection);
//                selectedCellsSeq._endChange();
            }

            fireCustomSelectedCellsListChangeEvent(change);
        }

        @Override public void select(int row) {
            select(row, null);
        }

        @Override public void select(int row, TableColumnBase<TreeItem<S>,?> column) {
            // TODO we need to bring in the TreeView selection stuff here...
            if (row < 0 || row >= getRowCount()) return;

            // if I'm in cell selection mode but the column is null, select each
            // of the contained cells individually
            if (isCellSelectionEnabled() && column == null) {
                List<TreeTableColumn<S,?>> columns = getTreeTableView().getVisibleLeafColumns();
                for (int i = 0; i < columns.size(); i++) {
                    select(row, columns.get(i));
                }
                return;
            }

            if (TableCellBehavior.hasDefaultAnchor(treeTableView)) {
                TableCellBehavior.removeAnchor(treeTableView);
            }

            if (getSelectionMode() == SelectionMode.SINGLE) {
                quietClearSelection();
            }
            selectedCellsMap.add(new TreeTablePosition<>(getTreeTableView(), row, (TreeTableColumn<S,?>)column));

            updateSelectedIndex(row);
            focus(row, (TreeTableColumn<S, ?>) column);
        }

        @Override public void select(TreeItem<S> obj) {
            if (obj == null && getSelectionMode() == SelectionMode.SINGLE) {
                clearSelection();
                return;
            }

            int firstIndex = treeTableView.getRow(obj);
            if (firstIndex > -1) {
                if (isSelected(firstIndex)) {
                    return;
                }

                if (getSelectionMode() == SelectionMode.SINGLE) {
                    quietClearSelection();
                }

                select(firstIndex);
            } else {
                // if we are here, we did not find the item in the entire data model.
                // Even still, we allow for this item to be set to the give object.
                // We expect that in concrete subclasses of this class we observe the
                // data model such that we check to see if the given item exists in it,
                // whilst SelectedIndex == -1 && SelectedItem != null.
                setSelectedIndex(-1);
                setSelectedItem(obj);
            }
        }

        @Override public void selectIndices(int row, int... rows) {
            if (rows == null) {
                select(row);
                return;
            }

            /*
             * Performance optimisation - if multiple selection is disabled, only
             * process the end-most row index.
             */
            int rowCount = getRowCount();

            if (getSelectionMode() == SelectionMode.SINGLE) {
                quietClearSelection();

                for (int i = rows.length - 1; i >= 0; i--) {
                    int index = rows[i];
                    if (index >= 0 && index < rowCount) {
                        select(index);
                        break;
                    }
                }

                if (selectedCellsMap.isEmpty()) {
                    if (row > 0 && row < rowCount) {
                        select(row);
                    }
                }
            } else {
                int lastIndex = -1;
                Set<TreeTablePosition<S,?>> positions = new LinkedHashSet<>();

                // --- firstly, we special-case the non-varargs 'row' argument
                if (row >= 0 && row < rowCount) {
                    // if I'm in cell selection mode, we want to select each
                    // of the contained cells individually
                    if (isCellSelectionEnabled()) {
                        List<TreeTableColumn<S,?>> columns = getTreeTableView().getVisibleLeafColumns();
                        for (int column = 0; column < columns.size(); column++) {
                            if (! selectedCellsMap.isSelected(row, column)) {
                                positions.add(new TreeTablePosition<>(getTreeTableView(), row, columns.get(column)));
                            }
                        }
                    } else {
                        boolean match = selectedCellsMap.isSelected(row, -1);
                        if (!match) {
                            positions.add(new TreeTablePosition<>(getTreeTableView(), row, null));
                        }
                    }

                    lastIndex = row;
                }

                // --- now we iterate through all varargs values
                for (int i = 0; i < rows.length; i++) {
                    int index = rows[i];
                    if (index < 0 || index >= rowCount) continue;
                    lastIndex = index;

                    if (isCellSelectionEnabled()) {
                        List<TreeTableColumn<S,?>> columns = getTreeTableView().getVisibleLeafColumns();
                        for (int column = 0; column < columns.size(); column++) {
                            if (! selectedCellsMap.isSelected(index, column)) {
                                positions.add(new TreeTablePosition<>(getTreeTableView(), index, columns.get(column)));
                                lastIndex = index;
                            }
                        }
                    } else {
                        if (! selectedCellsMap.isSelected(index, -1)) {
                            // if we are here then we have successfully gotten through the for-loop above
                            positions.add(new TreeTablePosition<>(getTreeTableView(), index, null));
                        }
                    }
                }

                selectedCellsMap.addAll(positions);

                if (lastIndex != -1) {
                    select(lastIndex);
                }
            }
        }

        @Override public void selectAll() {
            if (getSelectionMode() == SelectionMode.SINGLE) return;

            if (isCellSelectionEnabled()) {
                List<TreeTablePosition<S,?>> indices = new ArrayList<>();
                TreeTableColumn<S,?> column;
                TreeTablePosition<S,?> tp = null;
                for (int col = 0; col < getTreeTableView().getVisibleLeafColumns().size(); col++) {
                    column = getTreeTableView().getVisibleLeafColumns().get(col);
                    for (int row = 0; row < getRowCount(); row++) {
                        tp = new TreeTablePosition<>(getTreeTableView(), row, column);
                        indices.add(tp);
                    }
                }
                selectedCellsMap.setAll(indices);

                if (tp != null) {
                    select(tp.getRow(), tp.getTableColumn());
                    focus(tp.getRow(), tp.getTableColumn());
                }
            } else {
                List<TreeTablePosition<S,?>> indices = new ArrayList<>();
                for (int i = 0; i < getRowCount(); i++) {
                    indices.add(new TreeTablePosition<>(getTreeTableView(), i, null));
                }
                selectedCellsMap.setAll(indices);

                int focusedIndex = getFocusedIndex();
                if (focusedIndex == -1) {
                    final int itemCount = getItemCount();
                    if (itemCount > 0) {
                        select(itemCount - 1);
                        focus(indices.get(indices.size() - 1));
                    }
                } else {
                    select(focusedIndex);
                    focus(focusedIndex);
                }
            }
        }

        @Override public void selectRange(int minRow, TableColumnBase<TreeItem<S>,?> minColumn,
                                          int maxRow, TableColumnBase<TreeItem<S>,?> maxColumn) {
            if (getSelectionMode() == SelectionMode.SINGLE) {
                quietClearSelection();
                select(maxRow, maxColumn);
                return;
            }

            startAtomic();

            final int itemCount = getItemCount();
            final boolean isCellSelectionEnabled = isCellSelectionEnabled();

            final int minColumnIndex = treeTableView.getVisibleLeafIndex((TreeTableColumn<S,?>)minColumn);
            final int maxColumnIndex = treeTableView.getVisibleLeafIndex((TreeTableColumn<S,?>)maxColumn);
            final int _minColumnIndex = Math.min(minColumnIndex, maxColumnIndex);
            final int _maxColumnIndex = Math.max(minColumnIndex, maxColumnIndex);

            final int _minRow = Math.min(minRow, maxRow);
            final int _maxRow = Math.max(minRow, maxRow);

            List<TreeTablePosition<S,?>> cellsToSelect = new ArrayList<>();

            for (int _row = _minRow; _row <= _maxRow; _row++) {
                // begin copy/paste of select(int, column) method (with some
                // slight modifications)
                if (_row < 0 || _row >= itemCount) continue;

                if (! isCellSelectionEnabled) {
                    cellsToSelect.add(new TreeTablePosition<>(treeTableView, _row, (TreeTableColumn<S,?>)minColumn));
                } else {
                    for (int _col = _minColumnIndex; _col <= _maxColumnIndex; _col++) {
                        final TreeTableColumn<S, ?> column = treeTableView.getVisibleLeafColumn(_col);

                        // if I'm in cell selection mode but the column is null, I don't want
                        // to select the whole row instead...
                        if (column == null && isCellSelectionEnabled) continue;

                        cellsToSelect.add(new TreeTablePosition<>(treeTableView, _row, column));
                        // end copy/paste
                    }
                }
            }

            // to prevent duplication we remove all currently selected cells from
            // our list of cells to select.
            cellsToSelect.removeAll(getSelectedCells());

            selectedCellsMap.addAll(cellsToSelect);
            stopAtomic();

            // fire off events
            // Note that focus and selection always goes to maxRow, not _maxRow.
            updateSelectedIndex(maxRow);
            focus(maxRow, (TreeTableColumn<S,?>)maxColumn);

            final TreeTableColumn<S,?> startColumn = (TreeTableColumn<S,?>)minColumn;
            final TreeTableColumn<S,?> endColumn = isCellSelectionEnabled ? (TreeTableColumn<S,?>)maxColumn : startColumn;
            final int startChangeIndex = selectedCellsMap.indexOf(new TreeTablePosition<>(treeTableView, minRow, startColumn));
            final int endChangeIndex = selectedCellsMap.indexOf(new TreeTablePosition<>(treeTableView, maxRow, endColumn));

            if (startChangeIndex > -1 && endChangeIndex > -1) {
                final int startIndex = Math.min(startChangeIndex, endChangeIndex);
                final int endIndex = Math.max(startChangeIndex, endChangeIndex);

                ListChangeListener.Change c = new NonIterableChange.SimpleAddChange<>(startIndex, endIndex + 1, selectedCellsSeq);
                fireCustomSelectedCellsListChangeEvent(c);
//                selectedCellsSeq.fireChange(() -> selectedCellsSeq._nextAdd(startIndex, endIndex + 1));
            }
        }

        @Override public void clearSelection(int index) {
            clearSelection(index, null);
        }

        @Override
        public void clearSelection(int row, TableColumnBase<TreeItem<S>,?> column) {
            clearSelection(new TreeTablePosition<S,Object>(getTreeTableView(), row, (TreeTableColumn)column));
        }

        private void clearSelection(TreeTablePosition<S,?> tp) {
            final boolean csMode = isCellSelectionEnabled();
            final int row = tp.getRow();
            final boolean columnIsNull = tp.getTableColumn() == null;

            List<TreeTablePosition> toRemove = new ArrayList<>();
            for (TreeTablePosition pos : getSelectedCells()) {
                if (!csMode) {
                    if (pos.getRow() == row) {
                        toRemove.add(pos);
                        break;
                    }
                } else {
                    if (columnIsNull && pos.getRow() == row) {
                        // if we are in cell selection mode and the column is null,
                        // we remove all items in the row
                        toRemove.add(pos);
                    } else if (pos.equals(tp)) {
                        toRemove.add(tp);
                        break;
                    }
                }
            }
            toRemove.stream().forEach(selectedCellsMap::remove);

            if (isEmpty() && ! isAtomic()) {
                updateSelectedIndex(-1);
                selectedCellsMap.clear();
            }
        }

        @Override public void clearSelection() {
            final List<TreeTablePosition<S,?>> removed = new ArrayList<>((Collection)getSelectedCells());

            quietClearSelection();

            if (! isAtomic()) {
                updateSelectedIndex(-1);
                focus(-1);

                if (!removed.isEmpty()) {
//                    selectedCellsSeq.fireChange(() -> selectedCellsSeq._nextRemove(0, removed));
                    ListChangeListener.Change<TreeTablePosition<S, ?>> c = new NonIterableChange<TreeTablePosition<S, ?>>(0, 0, selectedCellsSeq) {
                        @Override public List<TreeTablePosition<S, ?>> getRemoved() {
                            return removed;
                        }
                    };
                    fireCustomSelectedCellsListChangeEvent(c);
                }
            }
        }

        private void quietClearSelection() {
            startAtomic();
            selectedCellsMap.clear();
            stopAtomic();
        }

        @Override public boolean isSelected(int index) {
            return isSelected(index, null);
        }

        @Override public boolean isSelected(int row, TableColumnBase<TreeItem<S>,?> column) {
            // When in cell selection mode, if the column is null, then we interpret
            // the users query to be asking if _all_ of the cells in the row are selected,
            // rather than if _any_ of the cells in the row are selected.
            final boolean isCellSelectionEnabled = isCellSelectionEnabled();
            if (isCellSelectionEnabled && column == null) {
                int columnCount = treeTableView.getVisibleLeafColumns().size();
                for (int col = 0; col < columnCount; col++) {
                    if (!selectedCellsMap.isSelected(row, col)) {
                        return false;
                    }
                }
                return true;
            } else {
                int columnIndex = !isCellSelectionEnabled || column == null ? -1 : treeTableView.getVisibleLeafIndex((TreeTableColumn<S, ?>) column);
                return selectedCellsMap.isSelected(row, columnIndex);
            }
        }

        @Override public boolean isEmpty() {
            return selectedCellsMap.isEmpty();
        }

        @Override public void selectPrevious() {
            if (isCellSelectionEnabled()) {
                // in cell selection mode, we have to wrap around, going from
                // right-to-left, and then wrapping to the end of the previous line
                TreeTablePosition<S,?> pos = getFocusedCell();
                if (pos.getColumn() - 1 >= 0) {
                    // go to previous row
                    select(pos.getRow(), getTableColumn(pos.getTableColumn(), -1));
                } else if (pos.getRow() < getRowCount() - 1) {
                    // wrap to end of previous row
                    select(pos.getRow() - 1, getTableColumn(getTreeTableView().getVisibleLeafColumns().size() - 1));
                }
            } else {
                int focusIndex = getFocusedIndex();
                if (focusIndex == -1) {
                    select(getRowCount() - 1);
                } else if (focusIndex > 0) {
                    select(focusIndex - 1);
                }
            }
        }

        @Override public void selectNext() {
            if (isCellSelectionEnabled()) {
                // in cell selection mode, we have to wrap around, going from
                // left-to-right, and then wrapping to the start of the next line
                TreeTablePosition<S,?> pos = getFocusedCell();
                if (pos.getColumn() + 1 < getTreeTableView().getVisibleLeafColumns().size()) {
                    // go to next column
                    select(pos.getRow(), getTableColumn(pos.getTableColumn(), 1));
                } else if (pos.getRow() < getRowCount() - 1) {
                    // wrap to start of next row
                    select(pos.getRow() + 1, getTableColumn(0));
                }
            } else {
                int focusIndex = getFocusedIndex();
                if (focusIndex == -1) {
                    select(0);
                } else if (focusIndex < getRowCount() -1) {
                    select(focusIndex + 1);
                }
            }
        }

        @Override public void selectAboveCell() {
            TreeTablePosition<S,?> pos = getFocusedCell();
            if (pos.getRow() == -1) {
                select(getRowCount() - 1);
            } else if (pos.getRow() > 0) {
                select(pos.getRow() - 1, pos.getTableColumn());
            }
        }

        @Override public void selectBelowCell() {
            TreeTablePosition<S,?> pos = getFocusedCell();

            if (pos.getRow() == -1) {
                select(0);
            } else if (pos.getRow() < getRowCount() -1) {
                select(pos.getRow() + 1, pos.getTableColumn());
            }
        }

        @Override public void selectFirst() {
            TreeTablePosition<S,?> focusedCell = getFocusedCell();

            if (getSelectionMode() == SelectionMode.SINGLE) {
                quietClearSelection();
            }

            if (getRowCount() > 0) {
                if (isCellSelectionEnabled()) {
                    select(0, focusedCell.getTableColumn());
                } else {
                    select(0);
                }
            }
        }

        @Override public void selectLast() {
            TreeTablePosition<S,?> focusedCell = getFocusedCell();

            if (getSelectionMode() == SelectionMode.SINGLE) {
                quietClearSelection();
            }

            int numItems = getRowCount();
            if (numItems > 0 && getSelectedIndex() < numItems - 1) {
                if (isCellSelectionEnabled()) {
                    select(numItems - 1, focusedCell.getTableColumn());
                } else {
                    select(numItems - 1);
                }
            }
        }

        @Override public void selectLeftCell() {
            if (! isCellSelectionEnabled()) return;

            TreeTablePosition<S,?> pos = getFocusedCell();
            if (pos.getColumn() - 1 >= 0) {
                select(pos.getRow(), getTableColumn(pos.getTableColumn(), -1));
            }
        }

        @Override public void selectRightCell() {
            if (! isCellSelectionEnabled()) return;

            TreeTablePosition<S,?> pos = getFocusedCell();
            if (pos.getColumn() + 1 < getTreeTableView().getVisibleLeafColumns().size()) {
                select(pos.getRow(), getTableColumn(pos.getTableColumn(), 1));
            }
        }



        
                                                                    *
Support code                                                        *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Support code                                                        *
         *                                                                     *
         **********************************************************************/

        private void updateDefaultSelection() {
            // when the items list totally changes, we should clear out
            // the selection
            int newSelectionIndex = -1;
            TreeItem<S> selectedItem = getSelectedItem();
            if (selectedItem != null) {
                newSelectionIndex = treeTableView.getRow(selectedItem);
            }

            // we put focus onto the first item, if there is at least
            // one item in the list
            int newFocusIndex = newSelectionIndex != -1 ? newSelectionIndex : treeTableView.getExpandedItemCount() > 0 ? 0 : -1;

            clearSelection();
            select(newSelectionIndex, isCellSelectionEnabled() ? getTableColumn(0) : null);
            focus(newFocusIndex, isCellSelectionEnabled() ? getTableColumn(0) : null);
        }

        private TreeTableColumn<S,?> getTableColumn(int pos) {
            return getTreeTableView().getVisibleLeafColumn(pos);
        }

        // Gets a table column to the left or right of the current one, given an offset
        private TreeTableColumn<S,?> getTableColumn(TreeTableColumn<S,?> column, int offset) {
            int columnIndex = getTreeTableView().getVisibleLeafIndex(column);
            int newColumnIndex = columnIndex + offset;
            return getTreeTableView().getVisibleLeafColumn(newColumnIndex);
        }

        private void updateSelectedIndex(int row) {
            setSelectedIndex(row);
            setSelectedItem(getModelItem(row));
        }

        @Override public void focus(int row) {
            focus(row, null);
        }

        private void focus(int row, TreeTableColumn<S,?> column) {
            focus(new TreeTablePosition<>(getTreeTableView(), row, column));
        }

        private void focus(TreeTablePosition<S,?> pos) {
            if (getTreeTableView().getFocusModel() == null) return;

            getTreeTableView().getFocusModel().focus(pos.getRow(), pos.getTableColumn());
            getTreeTableView().notifyAccessibleAttributeChanged(AccessibleAttribute.FOCUS_ITEM);
        }

        @Override public int getFocusedIndex() {
            return getFocusedCell().getRow();
        }

        private TreeTablePosition<S,?> getFocusedCell() {
            if (treeTableView.getFocusModel() == null) {
                return new TreeTablePosition<>(treeTableView, -1, null);
            }
            return treeTableView.getFocusModel().getFocusedCell();
        }

        private int getRowCount() {
            return treeTableView.getExpandedItemCount();
        }

        private void fireCustomSelectedCellsListChangeEvent(ListChangeListener.Change<? extends TreeTablePosition<S,?>> c) {
            ControlUtils.updateSelectedIndices(this, c);

            if (isAtomic()) {
                return;
            }

            selectedCellsSeq.callObservers(new MappingChange<>(c, MappingChange.NOOP_MAP, selectedCellsSeq));
        }
    }




    
A FocusModel with additional functionality to support the requirements of a TableView control. 
See Also:
TableView
Since:
JavaFX 8.0/**
     * A {@link FocusModel} with additional functionality to support the requirements
     * of a TableView control.
     *
     * @see TableView
     * @since JavaFX 8.0
     */
    public static class TreeTableViewFocusModel<S> extends TableFocusModel<TreeItem<S>, TreeTableColumn<S,?>> {

        private final TreeTableView<S> treeTableView;

        private final TreeTablePosition EMPTY_CELL;

        
Creates a default TableViewFocusModel instance that will be used to
manage focus of the provided TableView control.
Params:
treeTableView – The tableView upon which this focus model operates.
Throws:
NullPointerException – The TableView argument can not be null./**
         * Creates a default TableViewFocusModel instance that will be used to
         * manage focus of the provided TableView control.
         *
         * @param treeTableView The tableView upon which this focus model operates.
         * @throws NullPointerException The TableView argument can not be null.
         */
        public TreeTableViewFocusModel(final TreeTableView<S> treeTableView) {
            if (treeTableView == null) {
                throw new NullPointerException("TableView can not be null");
            }

            this.treeTableView = treeTableView;
            this.EMPTY_CELL = new TreeTablePosition<>(treeTableView, -1, null);

            this.treeTableView.rootProperty().addListener(weakRootPropertyListener);
            updateTreeEventListener(null, treeTableView.getRoot());

            int focusRow = getItemCount() > 0 ? 0 : -1;
            TreeTablePosition<S,?> pos = new TreeTablePosition<>(treeTableView, focusRow, null);
            setFocusedCell(pos);

            treeTableView.showRootProperty().addListener(o -> {
                if (isFocused(0)) {
                    focus(-1);
                    focus(0);
                }
            });

            focusedCellProperty().addListener(o -> {
                treeTableView.notifyAccessibleAttributeChanged(AccessibleAttribute.FOCUS_ITEM);
            });
        }

        private final ChangeListener<TreeItem<S>> rootPropertyListener = (observable, oldValue, newValue) -> {
            updateTreeEventListener(oldValue, newValue);
        };

        private final WeakChangeListener<TreeItem<S>> weakRootPropertyListener =
                new WeakChangeListener<>(rootPropertyListener);

        private void updateTreeEventListener(TreeItem<S> oldRoot, TreeItem<S> newRoot) {
            if (oldRoot != null && weakTreeItemListener != null) {
                oldRoot.removeEventHandler(TreeItem.<S>expandedItemCountChangeEvent(), weakTreeItemListener);
            }

            if (newRoot != null) {
                weakTreeItemListener = new WeakEventHandler<>(treeItemListener);
                newRoot.addEventHandler(TreeItem.<S>expandedItemCountChangeEvent(), weakTreeItemListener);
            }
        }

        private EventHandler<TreeItem.TreeModificationEvent<S>> treeItemListener = new EventHandler<TreeItem.TreeModificationEvent<S>>() {
            @Override public void handle(TreeItem.TreeModificationEvent<S> e) {
                // don't shift focus if the event occurred on a tree item after
                // the focused row, or if there is no focus index at present
                if (getFocusedIndex() == -1) return;

                int shift = 0;
                if (e.getChange() != null) {
                    e.getChange().next();
                }

                do {
                    int row = treeTableView.getRow(e.getTreeItem());

                    if (e.wasExpanded()) {
                        if (row < getFocusedIndex()) {
                            // need to shuffle selection by the number of visible children
                            shift += e.getTreeItem().getExpandedDescendentCount(false) - 1;
                        }
                    } else if (e.wasCollapsed()) {
                        if (row < getFocusedIndex()) {
                            // need to shuffle selection by the number of visible children
                            // that were just hidden
                            shift += -e.getTreeItem().previousExpandedDescendentCount + 1;
                        }
                    } else if (e.wasAdded()) {
                        // get the TreeItem the event occurred on - we only need to
                        // shift if the tree item is expanded
                        TreeItem<S> eventTreeItem = e.getTreeItem();
                        if (eventTreeItem.isExpanded()) {
                            for (int i = 0; i < e.getAddedChildren().size(); i++) {
                                // get the added item and determine the row it is in
                                TreeItem<S> item = e.getAddedChildren().get(i);
                                row = treeTableView.getRow(item);

                                if (item != null && row <= (shift+getFocusedIndex())) {
                                    shift += item.getExpandedDescendentCount(false);
                                }
                            }
                        }
                    } else if (e.wasRemoved()) {
                        row += e.getFrom() + 1;

                        for (int i = 0; i < e.getRemovedChildren().size(); i++) {
                            TreeItem<S> item = e.getRemovedChildren().get(i);
                            if (item != null && item.equals(getFocusedItem())) {
                                focus(Math.max(0, getFocusedIndex() - 1));
                                return;
                            }
                        }

                        if (row <= getFocusedIndex()) {
                            // shuffle selection by the number of removed items
                            shift += e.getTreeItem().isExpanded() ? -e.getRemovedSize() : 0;
                        }
                    }
                } while (e.getChange() != null && e.getChange().next());

                if (shift != 0) {
                    TreeTablePosition<S, ?> focusedCell = getFocusedCell();
                    final int newFocus = focusedCell.getRow() + shift;
                    if (newFocus >= 0) {
                        Platform.runLater(() -> focus(newFocus, focusedCell.getTableColumn()));
                    }
                }
            }
        };

        private WeakEventHandler<TreeItem.TreeModificationEvent<S>> weakTreeItemListener;

        
{@inheritDoc} /** {@inheritDoc} */
        @Override protected int getItemCount() {
//            if (tableView.getItems() == null) return -1;
//            return tableView.getItems().size();
            return treeTableView.getExpandedItemCount();
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override protected TreeItem<S> getModelItem(int index) {
            if (index < 0 || index >= getItemCount()) return null;
            return treeTableView.getTreeItem(index);
        }

        
The position of the current item in the TableView which has the focus.
/**
         * The position of the current item in the TableView which has the focus.
         */
        private ReadOnlyObjectWrapper<TreeTablePosition<S,?>> focusedCell;
        public final ReadOnlyObjectProperty<TreeTablePosition<S,?>> focusedCellProperty() {
            return focusedCellPropertyImpl().getReadOnlyProperty();
        }
        private void setFocusedCell(TreeTablePosition<S,?> value) { focusedCellPropertyImpl().set(value);  }
        public final TreeTablePosition<S,?> getFocusedCell() { return focusedCell == null ? EMPTY_CELL : focusedCell.get(); }

        private ReadOnlyObjectWrapper<TreeTablePosition<S,?>> focusedCellPropertyImpl() {
            if (focusedCell == null) {
                focusedCell = new ReadOnlyObjectWrapper<TreeTablePosition<S,?>>(EMPTY_CELL) {
                    private TreeTablePosition<S,?> old;
                    @Override protected void invalidated() {
                        if (get() == null) return;

                        if (old == null || !old.equals(get())) {
                            setFocusedIndex(get().getRow());
                            setFocusedItem(getModelItem(getValue().getRow()));

                            old = get();
                        }
                    }

                    @Override
                    public Object getBean() {
                        return TreeTableView.TreeTableViewFocusModel.this;
                    }

                    @Override
                    public String getName() {
                        return "focusedCell";
                    }
                };
            }
            return focusedCell;
        }


        
Causes the item at the given index to receive the focus.
Params:
row – The row index of the item to give focus to.
column – The column of the item to give focus to. Can be null./**
         * Causes the item at the given index to receive the focus.
         *
         * @param row The row index of the item to give focus to.
         * @param column The column of the item to give focus to. Can be null.
         */
        @Override public void focus(int row, TreeTableColumn<S,?> column) {
            if (row < 0 || row >= getItemCount()) {
                setFocusedCell(EMPTY_CELL);
            } else {
                TreeTablePosition<S,?> oldFocusCell = getFocusedCell();
                TreeTablePosition<S,?> newFocusCell = new TreeTablePosition<>(treeTableView, row, column);
                setFocusedCell(newFocusCell);

                if (newFocusCell.equals(oldFocusCell)) {
                    // manually update the focus properties to ensure consistency
                    setFocusedIndex(row);
                    setFocusedItem(getModelItem(row));
                }
            }
        }

        
Convenience method for setting focus on a particular row or cell using a TablePosition. 
Params:
pos – The table position where focus should be set./**
         * Convenience method for setting focus on a particular row or cell
         * using a {@link TablePosition}.
         *
         * @param pos The table position where focus should be set.
         */
        public void focus(TreeTablePosition<S,?> pos) {
            if (pos == null) return;
            focus(pos.getRow(), pos.getTableColumn());
        }


        /***********************************************************************
         *                                                                     *
         * Public API                                                          *
         *                                                                     *
         **********************************************************************/

        
Tests whether the row / cell at the given location currently has the
focus within the TableView.
/**
         * Tests whether the row / cell at the given location currently has the
         * focus within the TableView.
         */
        @Override public boolean isFocused(int row, TreeTableColumn<S,?> column) {
            if (row < 0 || row >= getItemCount()) return false;

            TreeTablePosition<S,?> cell = getFocusedCell();
            boolean columnMatch = column == null || column.equals(cell.getTableColumn());

            return cell.getRow() == row && columnMatch;
        }

        
Causes the item at the given index to receive the focus. This does not
cause the current selection to change. Updates the focusedItem and
focusedIndex properties such that focusedIndex = -1 unless
0 <= index < model size
.
Params:
index – The index of the item to get focus./**
         * Causes the item at the given index to receive the focus. This does not
         * cause the current selection to change. Updates the focusedItem and
         * focusedIndex properties such that <code>focusedIndex = -1</code> unless
         * <pre><code>0 &lt;= index &lt; model size</code></pre>.
         *
         * @param index The index of the item to get focus.
         */
        @Override public void focus(int index) {
            if (treeTableView.expandedItemCountDirty) {
                treeTableView.updateExpandedItemCount(treeTableView.getRoot());
            }

            if (index < 0 || index >= getItemCount()) {
                setFocusedCell(EMPTY_CELL);
            } else {
                setFocusedCell(new TreeTablePosition<>(treeTableView, index, null));
            }
        }

        
Attempts to move focus to the cell above the currently focused cell.
/**
         * Attempts to move focus to the cell above the currently focused cell.
         */
        @Override public void focusAboveCell() {
            TreeTablePosition<S,?> cell = getFocusedCell();

            if (getFocusedIndex() == -1) {
                focus(getItemCount() - 1, cell.getTableColumn());
            } else if (getFocusedIndex() > 0) {
                focus(getFocusedIndex() - 1, cell.getTableColumn());
            }
        }

        
Attempts to move focus to the cell below the currently focused cell.
/**
         * Attempts to move focus to the cell below the currently focused cell.
         */
        @Override public void focusBelowCell() {
            TreeTablePosition<S,?> cell = getFocusedCell();
            if (getFocusedIndex() == -1) {
                focus(0, cell.getTableColumn());
            } else if (getFocusedIndex() != getItemCount() -1) {
                focus(getFocusedIndex() + 1, cell.getTableColumn());
            }
        }

        
Attempts to move focus to the cell to the left of the currently focused cell.
/**
         * Attempts to move focus to the cell to the left of the currently focused cell.
         */
        @Override public void focusLeftCell() {
            TreeTablePosition<S,?> cell = getFocusedCell();
            if (cell.getColumn() <= 0) return;
            focus(cell.getRow(), getTableColumn(cell.getTableColumn(), -1));
        }

        
Attempts to move focus to the cell to the right of the the currently focused cell.
/**
         * Attempts to move focus to the cell to the right of the the currently focused cell.
         */
        @Override public void focusRightCell() {
            TreeTablePosition<S,?> cell = getFocusedCell();
            if (cell.getColumn() == getColumnCount() - 1) return;
            focus(cell.getRow(), getTableColumn(cell.getTableColumn(), 1));
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void focusPrevious() {
            if (getFocusedIndex() == -1) {
                focus(0);
            } else if (getFocusedIndex() > 0) {
                focusAboveCell();
            }
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void focusNext() {
            if (getFocusedIndex() == -1) {
                focus(0);
            } else if (getFocusedIndex() != getItemCount() -1) {
                focusBelowCell();
            }
        }



         
                                                                    *
Private Implementation                                              *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Private Implementation                                              *
         *                                                                     *
         **********************************************************************/

        private int getColumnCount() {
            return treeTableView.getVisibleLeafColumns().size();
        }

        // Gets a table column to the left or right of the current one, given an offset
        private TreeTableColumn<S,?> getTableColumn(TreeTableColumn<S,?> column, int offset) {
            int columnIndex = treeTableView.getVisibleLeafIndex(column);
            int newColumnIndex = columnIndex + offset;
            return treeTableView.getVisibleLeafColumn(newColumnIndex);
        }
    }
}