java/8 : java/awt/dnd/DragSourceContext.java

DragSourceContext
https://openjdk.java.net/
GPLv2 + Classpath Exception
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package java.awt.dnd;

import java.awt.Component;
import java.awt.Cursor;
import java.awt.Image;
import java.awt.Point;

import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;

import java.awt.dnd.peer.DragSourceContextPeer;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.Serializable;

import java.util.TooManyListenersException;

The DragSourceContext class is responsible for managing the initiator side of the Drag and Drop protocol. In particular, it is responsible for managing drag event notifications to the DragSourceListeners and DragSourceMotionListeners, and providing the Transferable representing the source data for the drag operation. 
Note that the DragSourceContext itself
implements the DragSourceListener and
DragSourceMotionListener interfaces. This is to allow the platform peer (the DragSourceContextPeer instance) created by the DragSource to notify the DragSourceContext of
state changes in the ongoing operation. This allows the
DragSourceContext object to interpose
itself between the platform and the
listeners provided by the initiator of the drag operation.

 By default, DragSourceContext sets the cursor as appropriate for the current state of the drag and drop operation. For example, if the user has chosen the move action, and the pointer is over a target that accepts the move action, the default move cursor is shown. When the pointer is over an area that does not accept the transfer, the default "no drop" cursor is shown. 
 This default handling mechanism is disabled when a custom cursor is set by the setCursor method. When the default handling is disabled, it becomes the responsibility of the developer to keep the cursor up to date, by listening to the DragSource events and calling the setCursor() method. Alternatively, you can provide custom cursor behavior by providing custom implementations of the DragSource and the DragSourceContext classes. 
See Also: DragSourceListener
DragSourceMotionListener
DnDConstants
Since: 1.2/**
 * The <code>DragSourceContext</code> class is responsible for managing the
 * initiator side of the Drag and Drop protocol. In particular, it is responsible
 * for managing drag event notifications to the
 * {@linkplain DragSourceListener DragSourceListeners}
 * and {@linkplain DragSourceMotionListener DragSourceMotionListeners}, and providing the
 * {@link Transferable} representing the source data for the drag operation.
 * <p>
 * Note that the <code>DragSourceContext</code> itself
 * implements the <code>DragSourceListener</code> and
 * <code>DragSourceMotionListener</code> interfaces.
 * This is to allow the platform peer
 * (the {@link DragSourceContextPeer} instance)
 * created by the {@link DragSource} to notify
 * the <code>DragSourceContext</code> of
 * state changes in the ongoing operation. This allows the
 * <code>DragSourceContext</code> object to interpose
 * itself between the platform and the
 * listeners provided by the initiator of the drag operation.
 * <p>
 * <a name="defaultCursor"></a>
 * By default, {@code DragSourceContext} sets the cursor as appropriate
 * for the current state of the drag and drop operation. For example, if
 * the user has chosen {@linkplain DnDConstants#ACTION_MOVE the move action},
 * and the pointer is over a target that accepts
 * the move action, the default move cursor is shown. When
 * the pointer is over an area that does not accept the transfer,
 * the default "no drop" cursor is shown.
 * <p>
 * This default handling mechanism is disabled when a custom cursor is set
 * by the {@link #setCursor} method. When the default handling is disabled,
 * it becomes the responsibility
 * of the developer to keep the cursor up to date, by listening
 * to the {@code DragSource} events and calling the {@code setCursor()} method.
 * Alternatively, you can provide custom cursor behavior by providing
 * custom implementations of the {@code DragSource}
 * and the {@code DragSourceContext} classes.
 *
 * @see DragSourceListener
 * @see DragSourceMotionListener
 * @see DnDConstants
 * @since 1.2
 */

public class DragSourceContext
    implements DragSourceListener, DragSourceMotionListener, Serializable {

    private static final long serialVersionUID = -115407898692194719L;

    // used by updateCurrentCursor

    An int used by updateCurrentCursor()
indicating that the Cursor should change
to the default (no drop) Cursor.
/**
     * An <code>int</code> used by updateCurrentCursor()
     * indicating that the <code>Cursor</code> should change
     * to the default (no drop) <code>Cursor</code>.
     */
    protected static final int DEFAULT = 0;

    An int used by updateCurrentCursor()
indicating that the Cursor
has entered a DropTarget.
/**
     * An <code>int</code> used by updateCurrentCursor()
     * indicating that the <code>Cursor</code>
     * has entered a <code>DropTarget</code>.
     */
    protected static final int ENTER   = 1;

    An int used by updateCurrentCursor()
indicating that the Cursor is
over a DropTarget.
/**
     * An <code>int</code> used by updateCurrentCursor()
     * indicating that the <code>Cursor</code> is
     * over a <code>DropTarget</code>.
     */
    protected static final int OVER    = 2;

    An int used by updateCurrentCursor()
indicating that the user operation has changed.
/**
     * An <code>int</code> used by updateCurrentCursor()
     * indicating that the user operation has changed.
     */

    protected static final int CHANGED = 3;

    Called from DragSource, this constructor creates a new
DragSourceContext given the
DragSourceContextPeer for this Drag, the
DragGestureEvent that triggered the Drag, the initial
Cursor to use for the Drag, an (optional)
Image to display while the Drag is taking place, the offset
of the Image origin from the hotspot at the instant of the
triggering event, the Transferable subject data, and the
DragSourceListener to use during the Drag and Drop
operation.


If DragSourceContextPeer is null
NullPointerException is thrown.


If DragGestureEvent is null
NullPointerException is thrown.


If Cursor is null no exception is thrown and
the default drag cursor behavior is activated for this drag operation.


If Image is null no exception is thrown.


If Image is not null and the offset is
null NullPointerException is thrown.


If Transferable is null
NullPointerException is thrown.


If DragSourceListener is null no exception
is thrown.
Params: dscp –       the DragSourceContextPeer for this drag
trigger –    the triggering event
dragCursor –  the initial Cursor for this drag operation or null for the default cursor handling; see class level documentation
                      for more details on the cursor handling mechanism during drag and drop
dragImage –  the Image to drag (or null)
offset –     the offset of the image origin from the hotspot at the
                  instant of the triggering event
t –          the Transferable
dsl –        the DragSourceListener
Throws: IllegalArgumentException – if the Component associated
        with the trigger event is null.
IllegalArgumentException – if the DragSource for the
        trigger event is null.
IllegalArgumentException – if the drag action for the
        trigger event is DnDConstants.ACTION_NONE.
IllegalArgumentException – if the source actions for the
        DragGestureRecognizer associated with the trigger
        event are equal to DnDConstants.ACTION_NONE.
NullPointerException – if dscp, trigger, or t are null, or
        if dragImage is non-null and offset is null/**
     * Called from <code>DragSource</code>, this constructor creates a new
     * <code>DragSourceContext</code> given the
     * <code>DragSourceContextPeer</code> for this Drag, the
     * <code>DragGestureEvent</code> that triggered the Drag, the initial
     * <code>Cursor</code> to use for the Drag, an (optional)
     * <code>Image</code> to display while the Drag is taking place, the offset
     * of the <code>Image</code> origin from the hotspot at the instant of the
     * triggering event, the <code>Transferable</code> subject data, and the
     * <code>DragSourceListener</code> to use during the Drag and Drop
     * operation.
     * <br>
     * If <code>DragSourceContextPeer</code> is <code>null</code>
     * <code>NullPointerException</code> is thrown.
     * <br>
     * If <code>DragGestureEvent</code> is <code>null</code>
     * <code>NullPointerException</code> is thrown.
     * <br>
     * If <code>Cursor</code> is <code>null</code> no exception is thrown and
     * the default drag cursor behavior is activated for this drag operation.
     * <br>
     * If <code>Image</code> is <code>null</code> no exception is thrown.
     * <br>
     * If <code>Image</code> is not <code>null</code> and the offset is
     * <code>null</code> <code>NullPointerException</code> is thrown.
     * <br>
     * If <code>Transferable</code> is <code>null</code>
     * <code>NullPointerException</code> is thrown.
     * <br>
     * If <code>DragSourceListener</code> is <code>null</code> no exception
     * is thrown.
     *
     * @param dscp       the <code>DragSourceContextPeer</code> for this drag
     * @param trigger    the triggering event
     * @param dragCursor     the initial {@code Cursor} for this drag operation
     *                       or {@code null} for the default cursor handling;
     *                       see <a href="DragSourceContext.html#defaultCursor">class level documentation</a>
     *                       for more details on the cursor handling mechanism during drag and drop
     * @param dragImage  the <code>Image</code> to drag (or <code>null</code>)
     * @param offset     the offset of the image origin from the hotspot at the
     *                   instant of the triggering event
     * @param t          the <code>Transferable</code>
     * @param dsl        the <code>DragSourceListener</code>
     *
     * @throws IllegalArgumentException if the <code>Component</code> associated
     *         with the trigger event is <code>null</code>.
     * @throws IllegalArgumentException if the <code>DragSource</code> for the
     *         trigger event is <code>null</code>.
     * @throws IllegalArgumentException if the drag action for the
     *         trigger event is <code>DnDConstants.ACTION_NONE</code>.
     * @throws IllegalArgumentException if the source actions for the
     *         <code>DragGestureRecognizer</code> associated with the trigger
     *         event are equal to <code>DnDConstants.ACTION_NONE</code>.
     * @throws NullPointerException if dscp, trigger, or t are null, or
     *         if dragImage is non-null and offset is null
     */
    public DragSourceContext(DragSourceContextPeer dscp,
                             DragGestureEvent trigger, Cursor dragCursor,
                             Image dragImage, Point offset, Transferable t,
                             DragSourceListener dsl) {
        if (dscp == null) {
            throw new NullPointerException("DragSourceContextPeer");
        }

        if (trigger == null) {
            throw new NullPointerException("Trigger");
        }

        if (trigger.getDragSource() == null) {
            throw new IllegalArgumentException("DragSource");
        }

        if (trigger.getComponent() == null) {
            throw new IllegalArgumentException("Component");
        }

        if (trigger.getSourceAsDragGestureRecognizer().getSourceActions() ==
                 DnDConstants.ACTION_NONE) {
            throw new IllegalArgumentException("source actions");
        }

        if (trigger.getDragAction() == DnDConstants.ACTION_NONE) {
            throw new IllegalArgumentException("no drag action");
        }

        if (t == null) {
            throw new NullPointerException("Transferable");
        }

        if (dragImage != null && offset == null) {
            throw new NullPointerException("offset");
        }

        peer         = dscp;
        this.trigger = trigger;
        cursor       = dragCursor;
        transferable = t;
        listener     = dsl;
        sourceActions =
            trigger.getSourceAsDragGestureRecognizer().getSourceActions();

        useCustomCursor = (dragCursor != null);

        updateCurrentCursor(trigger.getDragAction(), getSourceActions(), DEFAULT);
    }

    Returns the DragSource
that instantiated this DragSourceContext.
Returns: the DragSource that
  instantiated this DragSourceContext/**
     * Returns the <code>DragSource</code>
     * that instantiated this <code>DragSourceContext</code>.
     *
     * @return the <code>DragSource</code> that
     *   instantiated this <code>DragSourceContext</code>
     */

    public DragSource   getDragSource() { return trigger.getDragSource(); }

    Returns the Component associated with this
DragSourceContext.
Returns: the Component that started the drag/**
     * Returns the <code>Component</code> associated with this
     * <code>DragSourceContext</code>.
     *
     * @return the <code>Component</code> that started the drag
     */

    public Component    getComponent() { return trigger.getComponent(); }

    Returns the DragGestureEvent
that initially triggered the drag.
Returns: the Event that triggered the drag/**
     * Returns the <code>DragGestureEvent</code>
     * that initially triggered the drag.
     *
     * @return the Event that triggered the drag
     */

    public DragGestureEvent getTrigger() { return trigger; }

    Returns a bitwise mask of DnDConstants that
represent the set of drop actions supported by the drag source for the
drag operation associated with this DragSourceContext.
Returns: the drop actions supported by the drag source/**
     * Returns a bitwise mask of <code>DnDConstants</code> that
     * represent the set of drop actions supported by the drag source for the
     * drag operation associated with this <code>DragSourceContext</code>.
     *
     * @return the drop actions supported by the drag source
     */
    public int  getSourceActions() {
        return sourceActions;
    }

    Sets the cursor for this drag operation to the specified
Cursor.  If the specified Cursor
is null, the default drag cursor behavior is
activated for this drag operation, otherwise it is deactivated.
Params: c –  the initial Cursor for this drag operation, or null for the default cursor handling; see class
                      level documentation for more details on the cursor handling during drag and drop/**
     * Sets the cursor for this drag operation to the specified
     * <code>Cursor</code>.  If the specified <code>Cursor</code>
     * is <code>null</code>, the default drag cursor behavior is
     * activated for this drag operation, otherwise it is deactivated.
     *
     * @param c     the initial {@code Cursor} for this drag operation,
     *                       or {@code null} for the default cursor handling;
     *                       see {@linkplain Cursor class
     *                       level documentation} for more details
     *                       on the cursor handling during drag and drop
     *
     */

    public synchronized void setCursor(Cursor c) {
        useCustomCursor = (c != null);
        setCursorImpl(c);
    }

    Returns the current drag Cursor.

Returns: the current drag Cursor/**
     * Returns the current drag <code>Cursor</code>.
     * <P>
     * @return the current drag <code>Cursor</code>
     */

    public Cursor getCursor() { return cursor; }

    Add a DragSourceListener to this
DragSourceContext if one has not already been added.
If a DragSourceListener already exists,
this method throws a TooManyListenersException.

Params: dsl – the DragSourceListener to add.
Note that while null is not prohibited,
it is not acceptable as a parameter.
Throws: TooManyListenersException – if
a DragSourceListener has already been added/**
     * Add a <code>DragSourceListener</code> to this
     * <code>DragSourceContext</code> if one has not already been added.
     * If a <code>DragSourceListener</code> already exists,
     * this method throws a <code>TooManyListenersException</code>.
     * <P>
     * @param dsl the <code>DragSourceListener</code> to add.
     * Note that while <code>null</code> is not prohibited,
     * it is not acceptable as a parameter.
     * <P>
     * @throws TooManyListenersException if
     * a <code>DragSourceListener</code> has already been added
     */

    public synchronized void addDragSourceListener(DragSourceListener dsl) throws TooManyListenersException {
        if (dsl == null) return;

        if (equals(dsl)) throw new IllegalArgumentException("DragSourceContext may not be its own listener");

        if (listener != null)
            throw new TooManyListenersException();
        else
            listener = dsl;
    }

    Removes the specified DragSourceListener
from  this DragSourceContext.
Params: dsl – the DragSourceListener to remove;
    note that while null is not prohibited,
    it is not acceptable as a parameter/**
     * Removes the specified <code>DragSourceListener</code>
     * from  this <code>DragSourceContext</code>.
     *
     * @param dsl the <code>DragSourceListener</code> to remove;
     *     note that while <code>null</code> is not prohibited,
     *     it is not acceptable as a parameter
     */

    public synchronized void removeDragSourceListener(DragSourceListener dsl) {
        if (listener != null && listener.equals(dsl)) {
            listener = null;
        } else
            throw new IllegalArgumentException();
    }

    Notifies the peer that the Transferable's
DataFlavors have changed.
/**
     * Notifies the peer that the <code>Transferable</code>'s
     * <code>DataFlavor</code>s have changed.
     */

    public void transferablesFlavorsChanged() {
        if (peer != null) peer.transferablesFlavorsChanged();
    }

    Calls dragEnter on the
DragSourceListeners registered with this
DragSourceContext and with the associated
DragSource, and passes them the specified
DragSourceDragEvent.
Params: dsde – the DragSourceDragEvent/**
     * Calls <code>dragEnter</code> on the
     * <code>DragSourceListener</code>s registered with this
     * <code>DragSourceContext</code> and with the associated
     * <code>DragSource</code>, and passes them the specified
     * <code>DragSourceDragEvent</code>.
     *
     * @param dsde the <code>DragSourceDragEvent</code>
     */
    public void dragEnter(DragSourceDragEvent dsde) {
        DragSourceListener dsl = listener;
        if (dsl != null) {
            dsl.dragEnter(dsde);
        }
        getDragSource().processDragEnter(dsde);

        updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), ENTER);
    }

    Calls dragOver on the
DragSourceListeners registered with this
DragSourceContext and with the associated
DragSource, and passes them the specified
DragSourceDragEvent.
Params: dsde – the DragSourceDragEvent/**
     * Calls <code>dragOver</code> on the
     * <code>DragSourceListener</code>s registered with this
     * <code>DragSourceContext</code> and with the associated
     * <code>DragSource</code>, and passes them the specified
     * <code>DragSourceDragEvent</code>.
     *
     * @param dsde the <code>DragSourceDragEvent</code>
     */
    public void dragOver(DragSourceDragEvent dsde) {
        DragSourceListener dsl = listener;
        if (dsl != null) {
            dsl.dragOver(dsde);
        }
        getDragSource().processDragOver(dsde);

        updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), OVER);
    }

    Calls dragExit on the
DragSourceListeners registered with this
DragSourceContext and with the associated
DragSource, and passes them the specified
DragSourceEvent.
Params: dse – the DragSourceEvent/**
     * Calls <code>dragExit</code> on the
     * <code>DragSourceListener</code>s registered with this
     * <code>DragSourceContext</code> and with the associated
     * <code>DragSource</code>, and passes them the specified
     * <code>DragSourceEvent</code>.
     *
     * @param dse the <code>DragSourceEvent</code>
     */
    public void dragExit(DragSourceEvent dse) {
        DragSourceListener dsl = listener;
        if (dsl != null) {
            dsl.dragExit(dse);
        }
        getDragSource().processDragExit(dse);

        updateCurrentCursor(DnDConstants.ACTION_NONE, DnDConstants.ACTION_NONE, DEFAULT);
    }

    Calls dropActionChanged on the
DragSourceListeners registered with this
DragSourceContext and with the associated
DragSource, and passes them the specified
DragSourceDragEvent.
Params: dsde – the DragSourceDragEvent/**
     * Calls <code>dropActionChanged</code> on the
     * <code>DragSourceListener</code>s registered with this
     * <code>DragSourceContext</code> and with the associated
     * <code>DragSource</code>, and passes them the specified
     * <code>DragSourceDragEvent</code>.
     *
     * @param dsde the <code>DragSourceDragEvent</code>
     */
    public void dropActionChanged(DragSourceDragEvent dsde) {
        DragSourceListener dsl = listener;
        if (dsl != null) {
            dsl.dropActionChanged(dsde);
        }
        getDragSource().processDropActionChanged(dsde);

        updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), CHANGED);
    }

    Calls dragDropEnd on the
DragSourceListeners registered with this
DragSourceContext and with the associated
DragSource, and passes them the specified
DragSourceDropEvent.
Params: dsde – the DragSourceDropEvent/**
     * Calls <code>dragDropEnd</code> on the
     * <code>DragSourceListener</code>s registered with this
     * <code>DragSourceContext</code> and with the associated
     * <code>DragSource</code>, and passes them the specified
     * <code>DragSourceDropEvent</code>.
     *
     * @param dsde the <code>DragSourceDropEvent</code>
     */
    public void dragDropEnd(DragSourceDropEvent dsde) {
        DragSourceListener dsl = listener;
        if (dsl != null) {
            dsl.dragDropEnd(dsde);
        }
        getDragSource().processDragDropEnd(dsde);
    }

    Calls dragMouseMoved on the
DragSourceMotionListeners registered with the
DragSource associated with this
DragSourceContext, and them passes the specified
DragSourceDragEvent.
Params: dsde – the DragSourceDragEvent
Since: 1.4/**
     * Calls <code>dragMouseMoved</code> on the
     * <code>DragSourceMotionListener</code>s registered with the
     * <code>DragSource</code> associated with this
     * <code>DragSourceContext</code>, and them passes the specified
     * <code>DragSourceDragEvent</code>.
     *
     * @param dsde the <code>DragSourceDragEvent</code>
     * @since 1.4
     */
    public void dragMouseMoved(DragSourceDragEvent dsde) {
        getDragSource().processDragMouseMoved(dsde);
    }

    Returns the Transferable associated with
this DragSourceContext.
Returns: the Transferable/**
     * Returns the <code>Transferable</code> associated with
     * this <code>DragSourceContext</code>.
     *
     * @return the <code>Transferable</code>
     */
    public Transferable getTransferable() { return transferable; }

    If the default drag cursor behavior is active, this method
sets the default drag cursor for the specified actions
supported by the drag source, the drop target action,
and status, otherwise this method does nothing.
Params: sourceAct – the actions supported by the drag source
targetAct – the drop target action
status – one of the fields DEFAULT,
              ENTER, OVER,
              CHANGED/**
     * If the default drag cursor behavior is active, this method
     * sets the default drag cursor for the specified actions
     * supported by the drag source, the drop target action,
     * and status, otherwise this method does nothing.
     *
     * @param sourceAct the actions supported by the drag source
     * @param targetAct the drop target action
     * @param status one of the fields <code>DEFAULT</code>,
     *               <code>ENTER</code>, <code>OVER</code>,
     *               <code>CHANGED</code>
     */

    protected synchronized void updateCurrentCursor(int sourceAct, int targetAct, int status) {

        // if the cursor has been previously set then don't do any defaults
        // processing.

        if (useCustomCursor) {
            return;
        }

        // do defaults processing

        Cursor c = null;

        switch (status) {
            default:
                targetAct = DnDConstants.ACTION_NONE;
            case ENTER:
            case OVER:
            case CHANGED:
                int    ra = sourceAct & targetAct;

                if (ra == DnDConstants.ACTION_NONE) { // no drop possible
                    if ((sourceAct & DnDConstants.ACTION_LINK) == DnDConstants.ACTION_LINK)
                        c = DragSource.DefaultLinkNoDrop;
                    else if ((sourceAct & DnDConstants.ACTION_MOVE) == DnDConstants.ACTION_MOVE)
                        c = DragSource.DefaultMoveNoDrop;
                    else
                        c = DragSource.DefaultCopyNoDrop;
                } else { // drop possible
                    if ((ra & DnDConstants.ACTION_LINK) == DnDConstants.ACTION_LINK)
                        c = DragSource.DefaultLinkDrop;
                    else if ((ra & DnDConstants.ACTION_MOVE) == DnDConstants.ACTION_MOVE)
                        c = DragSource.DefaultMoveDrop;
                    else
                        c = DragSource.DefaultCopyDrop;
                }
        }

        setCursorImpl(c);
    }

    private void setCursorImpl(Cursor c) {
        if (cursor == null || !cursor.equals(c)) {
            cursor = c;
            if (peer != null) peer.setCursor(cursor);
        }
    }

    Serializes this DragSourceContext. This method first
performs default serialization. Next, this object's
Transferable is written out if and only if it can be
serialized. If not, null is written instead. In this case,
a DragSourceContext created from the resulting deserialized
stream will contain a dummy Transferable which supports no
DataFlavors. Finally, this object's
DragSourceListener is written out if and only if it can be
serialized. If not, null is written instead.
@serialData The default serializable fields, in alphabetical order,
            followed by either a Transferable instance, or
            null, followed by either a
            DragSourceListener instance, or
            null.
Since: 1.4/**
     * Serializes this <code>DragSourceContext</code>. This method first
     * performs default serialization. Next, this object's
     * <code>Transferable</code> is written out if and only if it can be
     * serialized. If not, <code>null</code> is written instead. In this case,
     * a <code>DragSourceContext</code> created from the resulting deserialized
     * stream will contain a dummy <code>Transferable</code> which supports no
     * <code>DataFlavor</code>s. Finally, this object's
     * <code>DragSourceListener</code> is written out if and only if it can be
     * serialized. If not, <code>null</code> is written instead.
     *
     * @serialData The default serializable fields, in alphabetical order,
     *             followed by either a <code>Transferable</code> instance, or
     *             <code>null</code>, followed by either a
     *             <code>DragSourceListener</code> instance, or
     *             <code>null</code>.
     * @since 1.4
     */
    private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();

        s.writeObject(SerializationTester.test(transferable)
                      ? transferable : null);
        s.writeObject(SerializationTester.test(listener)
                      ? listener : null);
    }

    Deserializes this DragSourceContext. This method first
performs default deserialization for all non-transient
fields. This object's Transferable and
DragSourceListener are then deserialized as well by using
the next two objects in the stream. If the resulting
Transferable is null, this object's
Transferable is set to a dummy Transferable
which supports no DataFlavors.
Since: 1.4/**
     * Deserializes this <code>DragSourceContext</code>. This method first
     * performs default deserialization for all non-<code>transient</code>
     * fields. This object's <code>Transferable</code> and
     * <code>DragSourceListener</code> are then deserialized as well by using
     * the next two objects in the stream. If the resulting
     * <code>Transferable</code> is <code>null</code>, this object's
     * <code>Transferable</code> is set to a dummy <code>Transferable</code>
     * which supports no <code>DataFlavor</code>s.
     *
     * @since 1.4
     */
    private void readObject(ObjectInputStream s)
        throws ClassNotFoundException, IOException
    {
        ObjectInputStream.GetField f = s.readFields();

        DragGestureEvent newTrigger = (DragGestureEvent)f.get("trigger", null);
        if (newTrigger == null) {
            throw new InvalidObjectException("Null trigger");
        }
        if (newTrigger.getDragSource() == null) {
            throw new InvalidObjectException("Null DragSource");
        }
        if (newTrigger.getComponent() == null) {
            throw new InvalidObjectException("Null trigger component");
        }

        int newSourceActions = f.get("sourceActions", 0)
                & (DnDConstants.ACTION_COPY_OR_MOVE | DnDConstants.ACTION_LINK);
        if (newSourceActions == DnDConstants.ACTION_NONE) {
            throw new InvalidObjectException("Invalid source actions");
        }
        int triggerActions = newTrigger.getDragAction();
        if (triggerActions != DnDConstants.ACTION_COPY &&
                triggerActions != DnDConstants.ACTION_MOVE &&
                triggerActions != DnDConstants.ACTION_LINK) {
            throw new InvalidObjectException("No drag action");
        }
        trigger = newTrigger;

        cursor = (Cursor)f.get("cursor", null);
        useCustomCursor = f.get("useCustomCursor", false);
        sourceActions = newSourceActions;

        transferable = (Transferable)s.readObject();
        listener = (DragSourceListener)s.readObject();

        // Implementation assumes 'transferable' is never null.
        if (transferable == null) {
            if (emptyTransferable == null) {
                emptyTransferable = new Transferable() {
                        public DataFlavor[] getTransferDataFlavors() {
                            return new DataFlavor[0];
                        }
                        public boolean isDataFlavorSupported(DataFlavor flavor)
                        {
                            return false;
                        }
                        public Object getTransferData(DataFlavor flavor)
                            throws UnsupportedFlavorException
                        {
                            throw new UnsupportedFlavorException(flavor);
                        }
                    };
            }
            transferable = emptyTransferable;
        }
    }

    private static Transferable emptyTransferable;

    /*
     * fields
     */

    private transient DragSourceContextPeer peer;

    The event which triggered the start of the drag.
@serial /**
     * The event which triggered the start of the drag.
     *
     * @serial
     */
    private DragGestureEvent    trigger;

    The current drag cursor.
@serial /**
     * The current drag cursor.
     *
     * @serial
     */
    private Cursor              cursor;

    private transient Transferable      transferable;

    private transient DragSourceListener    listener;

    true if the custom drag cursor is used instead of the
default one.
@serial /**
     * <code>true</code> if the custom drag cursor is used instead of the
     * default one.
     *
     * @serial
     */
    private boolean useCustomCursor;

    A bitwise mask of DnDConstants that represents the set of
drop actions supported by the drag source for the drag operation associated
with this DragSourceContext.
@serial /**
     * A bitwise mask of <code>DnDConstants</code> that represents the set of
     * drop actions supported by the drag source for the drag operation associated
     * with this <code>DragSourceContext.</code>
     *
     * @serial
     */
    private int sourceActions;
}
See Also:	DragSourceListener DragSourceMotionListener DnDConstants
Since:	1.2
Params:	dsl – the `DragSourceListener` to add. Note that while `null` is not prohibited, it is not acceptable as a parameter.
Throws:	TooManyListenersException – if a `DragSourceListener` has already been added
@serialData	The default serializable fields, in alphabetical order, followed by either a `Transferable` instance, or `null`, followed by either a `DragSourceListener` instance, or `null`.
Since:	1.4
/

java/ 8/ java/awt/dnd/DragSourceContext.java
