dragsourcecontext.java

JAVA基本类源代码,大家可以学习学习!

/*
 * @(#)DragSourceContext.java	1.50 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.dnd;

import java.awt.event.InputEvent;
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.DragGestureEvent;
import java.awt.dnd.DragSource;
import java.awt.dnd.DragSourceListener;
import java.awt.dnd.InvalidDnDOperationException;

import java.awt.dnd.peer.DragSourceContextPeer;

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

import java.util.TooManyListenersException;

/**
 * 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 <code>DragSourceListener</code>s
 * and <code>DragSourceMotionListener</code>s, and providing the
 * <code>Transferable</code> 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 <code>DragSourceContextPeer</code> instance) 
 * created by the <code>DragSource</code> to notify 
 * the <code>DragSourceContext</code> of
 * state changes in the ongoing operation. This allows the
 * <code>DragSourceContext</code> to interpose 
 * itself between the platform and the
 * listeners provided by the initiator of the drag operation.
 *
 * @see DragSourceListener
 * @see DragSourceMotionListener
 * @version 1.50, 01/23/03
 * @since 1.2
 */

public class DragSourceContext 
    implements DragSourceListener, DragSourceMotionListener, Serializable {

    private static final long serialVersionUID = -115407898692194719L;

    // used by updateCurrentCursor

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

    protected static final int CHANGED = 3;
	
    /**
     * 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</code> 
     * @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 <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 <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 <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 <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
     * <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 <code>Cursor</code> to display, or 
     *   <code>null</code> to activate the default drag cursor
     *   behavior
     * 
     */

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

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

    public Cursor getCursor() { return cursor; }

    /**
     * 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 <code>TooManyListenersException</code> 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 <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();