dragsource.java

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/*
 * @(#)DragSource.java	1.42 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.AWTError;
import java.awt.AWTException;
import java.awt.event.InputEvent;
import java.awt.AWTPermission;
import java.awt.Component;
import java.awt.Cursor;
import java.awt.GraphicsEnvironment;
import java.awt.HeadlessException;
import java.awt.Image;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.datatransfer.FlavorMap;
import java.awt.datatransfer.SystemFlavorMap;
import java.awt.datatransfer.Transferable;
import java.awt.dnd.peer.DragSourceContextPeer;
import java.io.Serializable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.security.AccessController;
import java.util.EventListener;
import sun.awt.dnd.SunDragSourceContextPeer;


/**
 * The <code>DragSource</code> is the entity responsible 
 * for the initiation of the Drag
 * and Drop operation, and may be used in a number of scenarios: 
 * <UL>
 * <LI>1 default instance per JVM for the lifetime of that JVM. 
 * <LI>1 instance per class of potential Drag Initiator object (e.g
 * TextField). [implementation dependent] 
 * <LI>1 per instance of a particular 
 * <code>Component</code>, or application specific
 * object associated with a <code>Component</code> 
 * instance in the GUI. [implementation dependent] 
 * <LI>Some other arbitrary association. [implementation dependent] 
 *</UL>
 *
 * Once the <code>DragSource</code> is 
 * obtained, a <code>DragGestureRecognizer</code> should
 * also be obtained to associate the <code>DragSource</code>
 * with a particular
 * <code>Component</code>. 
 * <P>
 * The initial interpretation of the user's gesture, 
 * and the subsequent starting of the drag operation 
 * are the responsibility of the implementing
 * <code>Component</code>, which is usually 
 * implemented by a <code>DragGestureRecognizer</code>. 
 *<P>
 * When a drag gesture occurs, the 
 * <code>DragSource</code>'s 
 * startDrag() method shall be
 * invoked in order to cause processing 
 * of the user's navigational
 * gestures and delivery of Drag and Drop 
 * protocol notifications. A
 * <code>DragSource</code> shall only 
 * permit a single Drag and Drop operation to be
 * current at any one time, and shall 
 * reject any further startDrag() requests
 * by throwing an <code>IllegalDnDOperationException</code> 
 * until such time as the extant operation is complete. 
 * <P>
 * The startDrag() method invokes the 
 * createDragSourceContext() method to
 * instantiate an appropriate 
 * <code>DragSourceContext</code> 
 * and associate the <code>DragSourceContextPeer</code>
 * with that. 
 * <P>
 * If the Drag and Drop System is 
 * unable to initiate a drag operation for
 * some reason, the startDrag() method throws 
 * a <code>java.awt.dnd.InvalidDnDOperationException</code>
 * to signal such a condition. Typically this 
 * exception is thrown when the underlying platform
 * system is either not in a state to 
 * initiate a drag, or the parameters specified are invalid. 
 * <P>
 * Note that during the drag, the 
 * set of operations exposed by the source
 * at the start of the drag operation may not change 
 * until the operation is complete. 
 * The operation(s) are constant for the
 * duration of the operation with respect to the 
 * <code>DragSource</code>. 
 *
 * @version 	1.42, 01/23/03
 * @since 1.2
 */

public class DragSource implements Serializable {

    private static final long serialVersionUID = 6236096958971414066L;

    /*
     * load a system default cursor
     */

    private static Cursor load(String name) {
        if (GraphicsEnvironment.isHeadless()) {
            return null;
        }

	try {
	    return (Cursor)Toolkit.getDefaultToolkit().getDesktopProperty(name);
	} catch (Exception e) {
	    e.printStackTrace();

	    throw new RuntimeException("failed to load system cursor: " + name + " : " + e.getMessage());
	}
    }

   
    /**
     * The default <code>Cursor</code> to use with a copy operation indicating
     * that a drop is currently allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultCopyDrop =
        load("DnD.Cursor.CopyDrop");

    /**
     * The default <code>Cursor</code> to use with a move operation indicating
     * that a drop is currently allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultMoveDrop =
        load("DnD.Cursor.MoveDrop");

    /**
     * The default <code>Cursor</code> to use with a link operation indicating
     * that a drop is currently allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultLinkDrop =
        load("DnD.Cursor.LinkDrop");

    /**
     * The default <code>Cursor</code> to use with a copy operation indicating
     * that a drop is currently not allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultCopyNoDrop =
        load("DnD.Cursor.CopyNoDrop");

    /**
     * The default <code>Cursor</code> to use with a move operation indicating
     * that a drop is currently not allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultMoveNoDrop =
        load("DnD.Cursor.MoveNoDrop");

    /**
     * The default <code>Cursor</code> to use with a link operation indicating 
     * that a drop is currently not allowed. <code>null</code> if
     * <code>GraphicsEnvironment.isHeadless()</code> returns <code>true</code>.
     *
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static final Cursor DefaultLinkNoDrop =
        load("DnD.Cursor.LinkNoDrop");

    private static final DragSource dflt =
        (GraphicsEnvironment.isHeadless()) ? null : new DragSource();

    /** 
     * Internal constants for serialization. 
     */
    static final String dragSourceListenerK = "dragSourceL";
    static final String dragSourceMotionListenerK = "dragSourceMotionL";

    /**
     * Gets the <code>DragSource</code> object associated with
     * the underlying platform.
     *
     * @return the platform DragSource
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     *            returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public static DragSource getDefaultDragSource() {
        if (GraphicsEnvironment.isHeadless()) {
            throw new HeadlessException();
        } else {
            return dflt;
        }
    }

    /**
     * Reports  
     * whether or not drag 
     * <code>Image</code> support 
     * is available on the underlying platform.
     * <P>
     * @return if the Drag Image support is available on this platform
     */

    public static boolean isDragImageSupported() {
	Toolkit t = Toolkit.getDefaultToolkit();

	Boolean supported;

	try {
	    supported = (Boolean)Toolkit.getDefaultToolkit().getDesktopProperty("DnD.isDragImageSupported");

	    return supported.booleanValue();
	} catch (Exception e) {
	    return false;
	}
    }

    /**
     * Creates a new <code>DragSource</code>.
     *
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     *            returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public DragSource() throws HeadlessException {
        if (GraphicsEnvironment.isHeadless()) {
            throw new HeadlessException();
        }
    }

    /**
     * Start a drag, given the <code>DragGestureEvent</code> 
     * that initiated the drag, the initial 
     * <code>Cursor</code> to use,
     * the <code>Image</code> to drag, 
     * the offset of the <code>Image</code> origin 
     * from the hotspot of the <code>Cursor</code> at 
     * the instant of the trigger,
     * the <code>Transferable</code> subject data 
     * of the drag, the <code>DragSourceListener</code>, 
     * and the <code>FlavorMap</code>. 
     * <P>
     * @param trigger	     the <code>DragGestureEvent</code> that initiated the drag
     * @param dragCursor     the initial <code>Cursor</code> or <code>null</code> for defaults
     * @param dragImage	     the image to drag or null,
     * @param imageOffset    the offset of the <code>Image</code> origin from the hotspot
     *			     of the <code>Cursor</code> at the instant of the trigger
     * @param transferable   the subject data of the drag
     * @param dsl	     the <code>DragSourceListener</code>
     * @param flavorMap	     the <code>FlavorMap</code> to use, or <code>null</code>
     * <P>
     * @throws <code>java.awt.dnd.InvalidDnDOperationException</code> 
     *    if the Drag and Drop
     *    system is unable to initiate a drag operation, or if the user
     *    attempts to start a drag while an existing drag operation 
     *    is still executing
     */

    public void startDrag(DragGestureEvent   trigger,
			  Cursor	     dragCursor,
			  Image		     dragImage,
			  Point		     imageOffset,
			  Transferable	     transferable,
			  DragSourceListener dsl,
			  FlavorMap	     flavorMap) throws InvalidDnDOperationException {

        SunDragSourceContextPeer.setDragDropInProgress(true);

        try {
            if (flavorMap != null) this.flavorMap = flavorMap;