/*
 * Copyright (c) 2008, 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
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 * questions.
 */

package javafx.scene.control;

import javafx.css.converter.SizeConverter;
import com.sun.javafx.scene.control.Properties;
import com.sun.javafx.scene.control.behavior.TreeCellBehavior;
import javafx.scene.control.skin.TreeViewSkin;

import javafx.application.Platform;
import javafx.beans.DefaultProperty;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.DoubleProperty;
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.ListChangeListener;
import javafx.css.CssMetaData;
import javafx.css.Styleable;
import javafx.css.StyleableDoubleProperty;
import javafx.css.StyleableProperty;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.event.EventType;
import javafx.event.WeakEventHandler;
import javafx.scene.AccessibleAttribute;
import javafx.scene.AccessibleRole;
import javafx.scene.control.TreeItem.TreeModificationEvent;
import javafx.scene.layout.Region;
import javafx.util.Callback;

import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

The TreeView control provides a view on to a tree root (of type TreeItem). By using a TreeView, it is possible to drill down into the children of a TreeItem, recursively until a TreeItem has no children (that is, it is a leaf node in the tree). To facilitate this, unlike controls like ListView, in TreeView it is necessary to only specify the root node. 
 For more information on building up a tree using this approach, refer to the TreeItem class documentation. Briefly however, to create a TreeView, you should do something along the lines of the following: 

TreeItem<String> root = new TreeItem<String>("Root Node");
root.setExpanded(true);
root.getChildren().addAll(
    new TreeItem<String>("Item 1"),
    new TreeItem<String>("Item 2"),
    new TreeItem<String>("Item 3")
);
TreeView<String> treeView = new TreeView<String>(root);

 A TreeView may be configured to optionally hide the root node by setting the showRoot property to false. If the root node is hidden, there is one less level of indentation, and all children nodes of the root node are shown. By default, the root node is shown in the TreeView. 
TreeView Selection / Focus APIs
To track selection and focus, it is necessary to become familiar with the SelectionModel and FocusModel classes. A TreeView 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 TreeView 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 TreeView instance, it is therefore necessary to do the following: 

treeView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
Customizing TreeView Visuals
The visuals of the TreeView can be entirely customized by replacing the default cell factory. A cell factory is used to generate TreeCell instances, which are used to represent an item in the TreeView. 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 TreeView, this is the responsibility of the cell factory. 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 TreeView, which you can observe by adding an EventHandler via setOnEditCommit(EventHandler). Similarly, you can also observe edit events for edit start and edit cancel.
By default the TreeView 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 EditEvent that is fired. It is simply a matter of calling EditEvent.getNewValue() to retrieve this value. 
It is very important to note that if you call 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 Node.addEventHandler(EventType<Event>, EventHandler<? super Event>) method to add a editCommitEvent() 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:
<T> – The type of the item contained within the TreeItem value property for all tree items in this TreeView.
See Also:
TreeItem
TreeCell
Since:
JavaFX 2.0/**
 * The TreeView control provides a view on to a tree root (of type
 * {@link TreeItem}). By using a TreeView, it is possible to drill down into the
 * children of a TreeItem, recursively until a TreeItem has no children (that is,
 * it is a <i>leaf</i> node in the tree). To facilitate this, unlike controls
 * like {@link ListView}, in TreeView it is necessary to <strong>only</strong>
 * specify the {@link #rootProperty() root} node.
 *
 * <p>
 * For more information on building up a tree using this approach, refer to the
 * {@link TreeItem} class documentation. Briefly however, to create a TreeView,
 * you should do something along the lines of the following:
 * <pre><code>
 * TreeItem&lt;String&gt; root = new TreeItem&lt;String&gt;("Root Node");
 * root.setExpanded(true);
 * root.getChildren().addAll(
 *     new TreeItem&lt;String&gt;("Item 1"),
 *     new TreeItem&lt;String&gt;("Item 2"),
 *     new TreeItem&lt;String&gt;("Item 3")
 * );
 * TreeView&lt;String&gt; treeView = new TreeView&lt;String&gt;(root);
 * </code></pre>
 *
 * <p>
 * A TreeView may be configured to optionally hide the root node by setting the
 * {@link #setShowRoot(boolean) showRoot} property to {@code false}. If the root
 * node is hidden, there is one less level of indentation, and all children
 * nodes of the root node are shown. By default, the root node is shown in the
 * TreeView.
 *
 * <h3>TreeView 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 TreeView 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 TreeView 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 TreeView instance, it is therefore necessary
 * to do the following:
 *
 * <pre>
 * {@code
 * treeView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);}</pre>
 *
 * <h3>Customizing TreeView Visuals</h3>
 * <p>The visuals of the TreeView can be entirely customized by replacing the
 * default {@link #cellFactoryProperty() cell factory}. A cell factory is used to
 * generate {@link TreeCell} instances, which are used to represent an item in the
 * TreeView. 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 TreeView, this is the responsibility
 * of the {@link #cellFactoryProperty() cell factory}. 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
 * TreeView, which you can observe by adding an {@link EventHandler} via
 * {@link TreeView#setOnEditCommit(javafx.event.EventHandler)}. Similarly,
 * you can also observe edit events for
 * {@link TreeView#setOnEditStart(javafx.event.EventHandler) edit start}
 * and {@link TreeView#setOnEditCancel(javafx.event.EventHandler) edit cancel}.</p>
 *
 * <p>By default the TreeView 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 EditEvent} that is fired. It is simply a matter of calling
 * {@link EditEvent#getNewValue()} to retrieve this value.
 *
 * <p>It is very important to note that if you call
 * {@link TreeView#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 TreeView#addEventHandler(javafx.event.EventType, javafx.event.EventHandler)}
 * method to add a {@link TreeView#editCommitEvent()} {@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 TreeItem
 * @see TreeCell
 * @param <T> The type of the item contained within the {@link TreeItem} value
 *      property for all tree items in this TreeView.
 * @since JavaFX 2.0
 */
@DefaultProperty("root")
public class TreeView<T> extends Control {

    /***************************************************************************
     *                                                                         *
     * 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:
<T> – the type of the TreeItem instances used in this TreeView
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 <T> the type of the TreeItem instances used in this TreeView
     * @return An EventType that indicates some edit event has occurred.
     */
    @SuppressWarnings("unchecked")
    public static <T> EventType<EditEvent<T>> editAnyEvent() {
        return (EventType<EditEvent<T>>) EDIT_ANY_EVENT;
    }
    private static final EventType<?> EDIT_ANY_EVENT =
            new EventType<>(Event.ANY, "TREE_VIEW_EDIT");

    
An EventType used to indicate that an edit event has started within the
TreeView upon which the event was fired.
Type parameters:
<T> – the type of the TreeItem instances used in this TreeView
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
     * TreeView upon which the event was fired.
     *
     * @param <T> the type of the TreeItem instances used in this TreeView
     * @return An EventType used to indicate that an edit event has started.
     */
    @SuppressWarnings("unchecked")
    public static <T> EventType<EditEvent<T>> editStartEvent() {
        return (EventType<EditEvent<T>>) 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 TreeView upon which the event was fired.
Type parameters:
<T> – the type of the TreeItem instances used in this TreeView
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 TreeView upon which the event was fired.
     *
     * @param <T> the type of the TreeItem instances used in this TreeView
     * @return An EventType used to indicate that an edit event has just been
     *      canceled.
     */
    @SuppressWarnings("unchecked")
    public static <T> EventType<EditEvent<T>> editCancelEvent() {
        return (EventType<EditEvent<T>>) 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 TreeView 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:
<T> – the type of the TreeItem instances used in this TreeView
Returns:
An EventType that is used to indicate that an edit in a TreeView
     has been committed./**
     * An EventType that is used to indicate that an edit in a TreeView has been
     * committed. This means that user has made changes to the data of a
     * TreeItem, and that the UI should be updated.
     *
     * @param <T> the type of the TreeItem instances used in this TreeView
     * @return An EventType that is used to indicate that an edit in a TreeView
     *      has been committed.
     */
    @SuppressWarnings("unchecked")
    public static <T> EventType<EditEvent<T>> editCommitEvent() {
        return (EventType<EditEvent<T>>) 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 TreeView 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 TreeView. 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 TreeView control, if the root node has a parent.
     * If this is important, call {@link TreeView#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 TreeView. As of JavaFX 8.0_20,
     *          the proper way to do this is via
     *          {@link TreeView#getTreeItemLevel(TreeItem)}
     */
    @Deprecated(since="8u20")
    public static int getNodeLevel(TreeItem<?> node) {
        if (node == null) return -1;

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

        return level;
    }


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

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

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

        setRoot(root);
        updateExpandedItemCount(root);

        // install default selection and focus models - it's unlikely this will be changed
        // by many users.
        MultipleSelectionModel<TreeItem<T>> sm = new TreeViewBitSetSelectionModel<T>(this);
        setSelectionModel(sm);
        setFocusModel(new TreeViewFocusModel<T>(this));
    }



    
                                                                        *
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<T>>> treeItemCacheMap = new HashMap<>();


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

    // we use this to forward events that have bubbled up TreeItem instances
    // to the TreeViewSkin, to force it to recalculate teh item count and redraw
    // if necessary
    private final EventHandler<TreeModificationEvent<T>> 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.<T>expandedItemCountChangeEvent())) {
                match = true;
                break;
            }
            eventType = eventType.getSuperType();
        }

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

    private WeakEventHandler<TreeModificationEvent<T>> weakRootEventListener;



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


    // --- Cell Factory
    private ObjectProperty<Callback<TreeView<T>, TreeCell<T>>> cellFactory;

    
Sets the cell factory that will be used for creating TreeCells,
which are used to represent items in the
TreeView. The factory works identically to the cellFactory in ListView
and other complex composite controls. It is called to create a new
TreeCell only when the system has determined that it doesn't have enough
cells to represent the currently visible items. The TreeCell is reused
by the system to represent different items in the tree when possible.
Refer to the Cell class documentation for more details. 
Params:
value – The Callback to use for generating TreeCell instances, or null if the default cell factory should be used./**
     * Sets the cell factory that will be used for creating TreeCells,
     * which are used to represent items in the
     * TreeView. The factory works identically to the cellFactory in ListView
     * and other complex composite controls. It is called to create a new
     * TreeCell only when the system has determined that it doesn't have enough
     * cells to represent the currently visible items. The TreeCell is reused
     * by the system to represent different items in the tree when possible.
     *
     * <p>Refer to the {@link Cell} class documentation for more details.
     *
     * @param value The {@link Callback} to use for generating TreeCell instances,
     *      or null if the default cell factory should be used.
     */
    public final void setCellFactory(Callback<TreeView<T>, TreeCell<T>> value) {
        cellFactoryProperty().set(value);
    }

    
Returns the cell factory that will be used for creating TreeCells,
which are used to represent items in the TreeView, or null if no custom
cell factory has been set.
Returns:
the cell factory/**
     * <p>Returns the cell factory that will be used for creating TreeCells,
     * which are used to represent items in the TreeView, or null if no custom
     * cell factory has been set.
     * @return the cell factory
     */
    public final Callback<TreeView<T>, TreeCell<T>> getCellFactory() {
        return cellFactory == null ? null : cellFactory.get();
    }

    
Represents the cell factory that will be used for creating TreeCells,
which are used to represent items in the TreeView.
Returns:
the cell factory property/**
     * Represents the cell factory that will be used for creating TreeCells,
     * which are used to represent items in the TreeView.
     * @return the cell factory property
     */
    public final ObjectProperty<Callback<TreeView<T>, TreeCell<T>>> cellFactoryProperty() {
        if (cellFactory == null) {
            cellFactory = new SimpleObjectProperty<Callback<TreeView<T>, TreeCell<T>>>(this, "cellFactory");
        }
        return cellFactory;
    }


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

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

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

            // Fix for RT-37853
            edit(null);

            expandedItemCountDirty = true;
            updateRootExpanded();
        }
    };

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

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

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



    // --- Show Root
    private BooleanProperty showRoot;

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

    
Property that represents whether or not the TreeView root node is visible.
Returns:
the show root property/**
     * Property that represents whether or not the TreeView 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;
    }


    // --- Selection Model
    private ObjectProperty<MultipleSelectionModel<TreeItem<T>>> selectionModel;

    
Sets the MultipleSelectionModel to be used in the TreeView. Despite a TreeView 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 TreeView.
     * Despite a TreeView 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(MultipleSelectionModel<TreeItem<T>> 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 MultipleSelectionModel<TreeItem<T>> 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 TreeView, 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 TreeView itself.
Returns:
the selection model property/**
     * The SelectionModel provides the API through which it is possible
     * to select single or multiple items within a TreeView, 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 TreeView itself.
     * @return the selection model property
     */
    public final ObjectProperty<MultipleSelectionModel<TreeItem<T>>> selectionModelProperty() {
        if (selectionModel == null) {
            selectionModel = new SimpleObjectProperty<MultipleSelectionModel<TreeItem<T>>>(this, "selectionModel");
        }
        return selectionModel;
    }


    // --- Focus Model
    private ObjectProperty<FocusModel<TreeItem<T>>> focusModel;

    
Sets the FocusModel to be used in the TreeView. 
Params:
value – the FocusModel to be used/**
     * Sets the {@link FocusModel} to be used in the TreeView.
     * @param value the {@link FocusModel} to be used
     */
    public final void setFocusModel(FocusModel<TreeItem<T>> 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 FocusModel<TreeItem<T>> 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 TreeView. 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 TreeView. Generally the
     * default implementation should be more than sufficient.
     * @return the focus model property
     */
    public final ObjectProperty<FocusModel<TreeItem<T>>> focusModelProperty() {
        if (focusModel == null) {
            focusModel = new SimpleObjectProperty<FocusModel<TreeItem<T>>>(this, "focusModel");
        }
        return focusModel;
    }


    // --- Expanded node count
    
Represents the number of tree nodes presently able to be visible in the
TreeView. 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.
Since:
JavaFX 8.0/**
     * <p>Represents the number of tree nodes presently able to be visible in the
     * TreeView. 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.
     * @since JavaFX 8.0
     */
    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();
    }


    // --- 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<TreeView<?>,Number> getCssMetaData() {
                    return StyleableProperties.FIXED_CELL_SIZE;
                }

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

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


    // --- 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 TreeView is editable - only if the TreeView 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 TreeView is editable - only if the TreeView 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 Item
    private ReadOnlyObjectWrapper<TreeItem<T>> editingItem;

    private void setEditingItem(TreeItem<T> value) {
        editingItemPropertyImpl().set(value);
    }

    
Returns the TreeItem that is currently being edited in the TreeView,
or null if no item is being edited.
Returns:
the TreeItem that is currently being edited in the TreeView/**
     * Returns the TreeItem that is currently being edited in the TreeView,
     * or null if no item is being edited.
     * @return the TreeItem that is currently being edited in the TreeView
     */
    public final TreeItem<T> getEditingItem() {
        return editingItem == null ? null : editingItem.get();
    }

    
A property used to represent the TreeItem currently being edited
in the TreeView, if editing is taking place, or null if no item is being edited.
It is not possible to set the editing item, instead it is required that you call edit(TreeItem). 
Returns:
the editing item property/**
     * <p>A property used to represent the TreeItem currently being edited
     * in the TreeView, if editing is taking place, or null if no item is being edited.
     *
     * <p>It is not possible to set the editing item, instead it is required that
     * you call {@link #edit(javafx.scene.control.TreeItem)}.
     * @return the editing item property
     */
    public final ReadOnlyObjectProperty<TreeItem<T>> editingItemProperty() {
        return editingItemPropertyImpl().getReadOnlyProperty();
    }

    private ReadOnlyObjectWrapper<TreeItem<T>> editingItemPropertyImpl() {
        if (editingItem == null) {
            editingItem = new ReadOnlyObjectWrapper<TreeItem<T>>(this, "editingItem");
        }
        return editingItem;
    }


    // --- On Edit Start
    private ObjectProperty<EventHandler<EditEvent<T>>> onEditStart;

    
Sets the EventHandler that will be called when the user begins an edit. 
Params:
value – the EventHandler that will be called when the user begins an edit/**
     * Sets the {@link EventHandler} that will be called when the user begins
     * an edit.
     * @param value the {@link EventHandler} that will be called when the user
     * begins an edit
     */
    public final void setOnEditStart(EventHandler<EditEvent<T>> value) {
        onEditStartProperty().set(value);
    }

    
Returns the EventHandler that will be called when the user begins an edit. 
Returns:
the EventHandler when the user begins an edit/**
     * Returns the {@link EventHandler} that will be called when the user begins
     * an edit.
     * @return the {@link EventHandler} when the user begins an edit
     */
    public final EventHandler<EditEvent<T>> getOnEditStart() {
        return onEditStart == null ? null : onEditStart.get();
    }

    
This event handler will be fired when the user successfully initiates
editing.
Returns:
the event handler when the user successfully initiates editing/**
     * This event handler will be fired when the user successfully initiates
     * editing.
     * @return the event handler when the user successfully initiates editing
     */
    public final ObjectProperty<EventHandler<EditEvent<T>>> onEditStartProperty() {
        if (onEditStart == null) {
            onEditStart = new SimpleObjectProperty<EventHandler<EditEvent<T>>>(this, "onEditStart") {
                @Override protected void invalidated() {
                    setEventHandler(TreeView.<T>editStartEvent(), get());
                }
            };
        }
        return onEditStart;
    }


    // --- On Edit Commit
    private ObjectProperty<EventHandler<EditEvent<T>>> onEditCommit;

    
Sets the EventHandler that will be called when the user commits an edit. 
Params:
value – the EventHandler that will be called when the user commits an edit/**
     * Sets the {@link EventHandler} that will be called when the user commits
     * an edit.
     * @param value the {@link EventHandler} that will be called when the user
     * commits an edit
     */
    public final void setOnEditCommit(EventHandler<EditEvent<T>> value) {
        onEditCommitProperty().set(value);
    }

    
Returns the EventHandler that will be called when the user commits an edit. 
Returns:
the EventHandler that will be called when the user commits an edit/**
     * Returns the {@link EventHandler} that will be called when the user commits
     * an edit.
     * @return the {@link EventHandler} that will be called when the user commits
     * an edit
     */
    public final EventHandler<EditEvent<T>> getOnEditCommit() {
        return onEditCommit == null ? null : onEditCommit.get();
    }

    
This property is used when the user performs an action that should
result in their editing input being persisted.
The EventHandler in this property should not be called directly - instead call TreeCell.commitEdit(Object) from within your custom TreeCell. This will handle firing this event, updating the view, and switching out of the editing state.
Returns:
the event handler when the user performs an action that result in
their editing input being persisted/**
     * <p>This property is used when the user performs an action that should
     * result in their editing input being persisted.</p>
     *
     * <p>The EventHandler in this property should not be called directly -
     * instead call {@link TreeCell#commitEdit(java.lang.Object)} from within
     * your custom TreeCell. This will handle firing this event, updating the
     * view, and switching out of the editing state.</p>
     * @return the event handler when the user performs an action that result in
     * their editing input being persisted
     */
    public final ObjectProperty<EventHandler<EditEvent<T>>> onEditCommitProperty() {
        if (onEditCommit == null) {
            onEditCommit = new SimpleObjectProperty<EventHandler<EditEvent<T>>>(this, "onEditCommit") {
                @Override protected void invalidated() {
                    setEventHandler(TreeView.<T>editCommitEvent(), get());
                }
            };
        }
        return onEditCommit;
    }


    // --- On Edit Cancel
    private ObjectProperty<EventHandler<EditEvent<T>>> onEditCancel;

    
Sets the EventHandler that will be called when the user cancels an edit. 
Params:
value – the EventHandler that will be called when the user cancels an edit/**
     * Sets the {@link EventHandler} that will be called when the user cancels
     * an edit.
     * @param value the {@link EventHandler} that will be called when the user
     * cancels an edit
     */
    public final void setOnEditCancel(EventHandler<EditEvent<T>> value) {
        onEditCancelProperty().set(value);
    }

    
Returns the EventHandler that will be called when the user cancels an edit. 
Returns:
the EventHandler that will be called when the user cancels an edit/**
     * Returns the {@link EventHandler} that will be called when the user cancels
     * an edit.
     * @return the {@link EventHandler} that will be called when the user cancels
     * an edit
     */
    public final EventHandler<EditEvent<T>> getOnEditCancel() {
        return onEditCancel == null ? null : onEditCancel.get();
    }

    
This event handler will be fired when the user cancels editing a cell.
Returns:
the event handler will be fired when the user cancels editing a
cell/**
     * This event handler will be fired when the user cancels editing a cell.
     * @return the event handler will be fired when the user cancels editing a
     * cell
     */
    public final ObjectProperty<EventHandler<EditEvent<T>>> onEditCancelProperty() {
        if (onEditCancel == null) {
            onEditCancel = new SimpleObjectProperty<EventHandler<EditEvent<T>>>(this, "onEditCancel") {
                @Override protected void invalidated() {
                    setEventHandler(TreeView.<T>editCancelEvent(), get());
                }
            };
        }
        return onEditCancel;
    }



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


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

        super.layoutChildren();
    }


    
Instructs the TreeView to begin editing the given TreeItem, if the TreeView is editable. Once this method is called, if the current cell factory is set up to support editing, the Cell will switch its visual state to enable the user input to take place. 
Params:
item – The TreeItem in the TreeView that should be edited./**
     * Instructs the TreeView to begin editing the given TreeItem, if
     * the TreeView is {@link #editableProperty() editable}. Once
     * this method is called, if the current
     * {@link #cellFactoryProperty() cell factory} is set up to support editing,
     * the Cell will switch its visual state to enable the user input to take place.
     *
     * @param item The TreeItem in the TreeView that should be edited.
     */
    public void edit(TreeItem<T> item) {
        if (!isEditable()) return;
        setEditingItem(item);
    }


    
Scrolls the TreeView 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 TreeView./**
     * Scrolls the TreeView 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 TreeView.
     */
    public void scrollTo(int index) {
        ControlUtils.scrollToIndex(this, index);
    }

    
Called when there's a request to scroll an index into view using scrollTo(int) 
Since:
JavaFX 8.0/**
     * Called when there's a request to scroll an index into view using {@link #scrollTo(int)}
     * @since JavaFX 8.0
     */
    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 TreeView.this;
                }

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

    
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 TreeView 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 TreeView 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<T> 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<T> 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<T>> treeItemRef = treeItemCacheMap.get(_row);
                TreeItem<T> treeItem = treeItemRef.get();
                if (treeItem != null) {
                    return treeItem;
                }
            }
        }

        TreeItem<T> 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 TreeView, 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 TreeView, 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;
    }

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

    
Calling refresh() forces the TreeView control to recreate and repopulate the cells necessary to populate the visual bounds of the control. In other words, this forces the TreeView 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 TreeView itself. 
Since:
JavaFX 8u60/**
     * Calling {@code refresh()} forces the TreeView control to recreate and
     * repopulate the cells necessary to populate the visual bounds of the control.
     * In other words, this forces the TreeView 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 TreeView itself.
     *
     * @since JavaFX 8u60
     */
    public void refresh() {
        getProperties().put(Properties.RECREATE, Boolean.TRUE);
    }



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

    private void updateExpandedItemCount(TreeItem<T> 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);
        }
    }



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

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

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

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

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

                    @Override public StyleableProperty<Number> getStyleableProperty(TreeView<?> 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.
Since:
JavaFX 8.0/**
     * @return The CssMetaData associated with this class, which may include the
     * CssMetaData of its superclasses.
     * @since JavaFX 8.0
     */
    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();
    }



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

    
{@inheritDoc} /** {@inheritDoc} */
    @Override
    public Object queryAccessibleAttribute(AccessibleAttribute attribute, Object... parameters) {
        switch (attribute) {
            case MULTIPLE_SELECTION: {
                MultipleSelectionModel<TreeItem<T>> sm = getSelectionModel();
                return sm != null && sm.getSelectionMode() == SelectionMode.MULTIPLE;
            }
            case ROW_COUNT: return getExpandedItemCount();
            default: return super.queryAccessibleAttribute(attribute, parameters);
        }
    }



    /***************************************************************************
     *                                                                         *
     * Support Interfaces                                                      *
     *                                                                         *
     **************************************************************************/



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


    
An Event subclass used specifically in TreeView 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:
<T> – The type of the input, which is the same type as the TreeView
     itself.
Since:
JavaFX 2.0/**
     * An {@link Event} subclass used specifically in TreeView 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 <T> The type of the input, which is the same type as the TreeView
     *      itself.
     * @since JavaFX 2.0
     */
    public static class EditEvent<T> extends Event {
        private static final long serialVersionUID = -4437033058917528976L;

        
Common supertype for all edit event types.
Since:
JavaFX 8.0/**
         * Common supertype for all edit event types.
         * @since JavaFX 8.0
         */
        public static final EventType<?> ANY = EDIT_ANY_EVENT;

        private final TreeView<T> source;
        private final T oldValue;
        private final T newValue;
        private transient final TreeItem<T> treeItem;

        
Creates a new EditEvent instance to represent an edit event. This event is used for TreeView.editStartEvent(), TreeView.editCommitEvent() and TreeView.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(TreeView<T> source,
                         EventType<? extends EditEvent> eventType,
                         TreeItem<T> treeItem, T oldValue, T newValue) {
            super(source, Event.NULL_SOURCE_TARGET, eventType);
            this.source = source;
            this.oldValue = oldValue;
            this.newValue = newValue;
            this.treeItem = treeItem;
        }

        
Returns the TreeView upon which the edit took place.
/**
         * Returns the TreeView upon which the edit took place.
         */
        @Override public TreeView<T> 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<T> 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 T 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 T getOldValue() {
            return oldValue;
        }
    }







    // package for testing
    static class TreeViewBitSetSelectionModel<T> extends MultipleSelectionModelBase<TreeItem<T>> {

        
                                                                    *
Internal fields                                                     *
                                                                    *
/***********************************************************************
         *                                                                     *
         * Internal fields                                                     *
         *                                                                     *
         **********************************************************************/

        private TreeView<T> treeView = null;



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

        public TreeViewBitSetSelectionModel(final TreeView<T> treeView) {
            if (treeView == null) {
                throw new IllegalArgumentException("TreeView can not be null");
            }

            this.treeView = treeView;
            this.treeView.rootProperty().addListener(weakRootPropertyListener);
            this.treeView.showRootProperty().addListener(o -> {
                shiftSelection(0, treeView.isShowRoot() ? 1 : -1, null);
            });

            updateTreeEventListener(null, treeView.getRoot());

            updateDefaultSelection();
        }

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

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

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

        private EventHandler<TreeModificationEvent<T>> treeItemListener = e -> {
            if (getSelectedIndex() == -1 && getSelectedItem() == null) return;

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

            treeView.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 = treeView.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;

                    selectedIndices._beginChange();
                    final int from = startRow + 1;
                    final int to = startRow + count;
                    final List<Integer> removed = new ArrayList<>();
                    for (int i = from; i < to; i++) {
                        if (isSelected(i)) {
                            wasAnyChildSelected = true;
                            removed.add(i);
                        }
                    }

                    ControlUtils.reducingChange(selectedIndices, removed);

                    for (int index : removed) {
                        startAtomic();
                        clearSelection(index);
                        stopAtomic();
                    }
                    selectedIndices._endChange();

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

                    shift += -count + 1;
                    startRow++;
                } else if (e.wasPermutated()) {
                    // no-op
                } 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 = treeView.getRow(e.getChange().getAddedSubList().get(0));
                } 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> selectedIndices1 = getSelectedIndices();
                    final int selectedIndex = getSelectedIndex();
                    final List<TreeItem<T>> selectedItems = getSelectedItems();
                    final TreeItem<T> selectedItem = getSelectedItem();
                    final List<? extends TreeItem<T>> removedChildren = e.getChange().getRemoved();

                    for (int i = 0; i < selectedIndices1.size() && !selectedItems.isEmpty(); i++) {
                        int index = selectedIndices1.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 (selectedIndex < getItemCount()) {
                                final int previousRow = selectedIndex == 0 ? 0 : selectedIndex - 1;
                                TreeItem<T> newSelectedItem = getModelItem(previousRow);
                                if (!selectedItem.equals(newSelectedItem)) {
                                    select(newSelectedItem);
                                }
                            }
                        }
                    }
                }
            } while (e.getChange() != null && e.getChange().next());

            shiftSelection(startRow, shift, null);

            if (e.wasAdded() || e.wasRemoved()) {
                Integer anchor = TreeCellBehavior.getAnchor(treeView, null);
                if (anchor != null && isSelected(anchor + shift)) {
                    TreeCellBehavior.setAnchor(treeView, anchor + shift, false);
                }
            }
        };

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

        private WeakEventHandler<TreeModificationEvent<T>> weakTreeItemListener;



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

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void selectAll() {
            // when a selectAll happens, the anchor should not change, so we store it
            // before, and restore it afterwards
            final int anchor = TreeCellBehavior.getAnchor(treeView, -1);
            super.selectAll();
            TreeCellBehavior.setAnchor(treeView, anchor, false);
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void select(TreeItem<T> obj) {
//        if (getRowCount() <= 0) return;

            if (obj == null && getSelectionMode() == SelectionMode.SINGLE) {
                clearSelection();
                return;
            }

            // we firstly expand the path down such that the given object is
            // visible. This fixes RT-14456, where selection was not happening
            // correctly on TreeItems that are not visible.

            if (obj != null) {
                TreeItem<?> item = obj.getParent();
                while (item != null) {
                    item.setExpanded(true);
                    item = item.getParent();
                }
            }

            // Fix for RT-15419. We eagerly update the tree item count, such that
            // selection occurs on the row
            treeView.updateExpandedItemCount(treeView.getRoot());

            // We have no option but to iterate through the model and select the
            // first occurrence of the given object. Once we find the first one, we
            // don't proceed to select any others.
            int row = treeView.getRow(obj);

            if (row == -1) {
                // 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);
            } else {
                select(row);
            }
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void clearAndSelect(int row) {
            TreeCellBehavior.setAnchor(treeView, row, false);
            super.clearAndSelect(row);
        }


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

        
{@inheritDoc} /** {@inheritDoc} */
        @Override protected void focus(int itemIndex) {
            if (treeView.getFocusModel() != null) {
                treeView.getFocusModel().focus(itemIndex);
            }

            // FIXME this is not the correct location for fire selection events (and does not take into account multiple selection)
            treeView.notifyAccessibleAttributeChanged(AccessibleAttribute.FOCUS_ITEM);
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override protected int getFocusedIndex() {
            if (treeView.getFocusModel() == null) return -1;
            return treeView.getFocusModel().getFocusedIndex();
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override protected int getItemCount() {
            return treeView == null ? 0 : treeView.getExpandedItemCount();
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public TreeItem<T> getModelItem(int index) {
            if (treeView == null) return null;

            if (index < 0 || index >= treeView.getExpandedItemCount()) return null;

            return treeView.getTreeItem(index);
        }



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

        private void updateDefaultSelection() {
            clearSelection();

            // we put focus onto the first item, if there is at least
            // one item in the list
            focus(getItemCount() > 0 ? 0 : -1);
        }
    }



    
Type parameters:
<T> – /**
     *
     * @param <T>
     */
    static class TreeViewFocusModel<T> extends FocusModel<TreeItem<T>> {

        private final TreeView<T> treeView;

        public TreeViewFocusModel(final TreeView<T> treeView) {
            this.treeView = treeView;
            this.treeView.rootProperty().addListener(weakRootPropertyListener);
            updateTreeEventListener(null, treeView.getRoot());

            if (treeView.getExpandedItemCount() > 0) {
                focus(0);
            }

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

            focusedIndexProperty().addListener(o -> {
                treeView.notifyAccessibleAttributeChanged(AccessibleAttribute.FOCUS_ITEM);
            });
        }

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

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

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

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

        private EventHandler<TreeModificationEvent<T>> treeItemListener = new EventHandler<TreeModificationEvent<T>>() {
            @Override public void handle(TreeModificationEvent<T> 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 row = treeView.getRow(e.getTreeItem());

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

                do {
                    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<T> 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<T> item = e.getAddedChildren().get(i);
                                row = treeView.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<T> 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) {
                    final int newFocus = getFocusedIndex() + shift;
                    if (newFocus >= 0) {
                        Platform.runLater(() -> focus(newFocus));
                    }
                }
            }
        };

        private WeakEventHandler<TreeModificationEvent<T>> weakTreeItemListener;

        @Override protected int getItemCount() {
            return treeView == null ? -1 : treeView.getExpandedItemCount();
        }

        @Override protected TreeItem<T> getModelItem(int index) {
            if (treeView == null) return null;

            if (index < 0 || index >= treeView.getExpandedItemCount()) return null;

            return treeView.getTreeItem(index);
        }

        
{@inheritDoc} /** {@inheritDoc} */
        @Override public void focus(int index) {
            if (treeView.expandedItemCountDirty) {
                treeView.updateExpandedItemCount(treeView.getRoot());
            }

            super.focus(index);
        }
    }
}