DropTargetListener


1   /*
2    * @(#)DropTargetListener.java  1.22 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.awt.dnd;
9   
10  import java.util.EventListener  ;
11  
12  import java.awt.dnd.DropTargetContext  ;
13  import java.awt.dnd.DropTargetDragEvent  ;
14  import java.awt.dnd.DropTargetDropEvent  ;
15  
16  /**
17   * The <code>DropTargetListener</code> interface 
18   * is the callback interface used by the
19   * <code>DropTarget</code> class to provide 
20   * notification of DnD operations that involve
21   * the subject <code>DropTarget</code>. Methods of
22   * this interface may be implemented to provide
23   * "drag under" visual feedback to the user throughout
24   * the Drag and Drop operation.
25   * <p>
26   * Create a listener object by implementing the interface and then register it
27   * with a <code>DropTarget</code>. When the drag enters, moves over, or exits
28   * the operable part of the drop site for that <code>DropTarget</code>, when 
29   * the drop action changes, and when the drop occurs, the relevant method in 
30   * the listener object is invoked, and the <code>DropTargetEvent</code> is 
31   * passed to it.
32   * <p>
33   * The operable part of the drop site for the <code>DropTarget</code> is 
34   * the part of the associated <code>Component</code>'s geometry that is not 
35   * obscured by an overlapping top-level window or by another 
36   * <code>Component</code> higher in the Z-order that has an associated active 
37   * <code>DropTarget</code>.
38   * <p>
39   * During the drag, the data associated with the current drag operation can be
40   * retrieved by calling <code>getTransferable()</code> on 
41   * <code>DropTargetDragEvent</code> instances passed to the listener's
42   * methods. 
43   * <p>
44   * Note that <code>getTransferable()</code> on the 
45   * <code>DropTargetDragEvent</code> instance should only be called within the
46   * respective listener's method and all the necessary data should be retrieved
47   * from the returned <code>Transferable</code> before that method returns.
48   *
49   * @version     1.22, 12/19/03
50   * @since 1.2
51   */
52  
53  public interface DropTargetListener extends EventListener   {
54  
55      /**
56       * Called while a drag operation is ongoing, when the mouse pointer enters
57       * the operable part of the drop site for the <code>DropTarget</code>
58       * registered with this listener. 
59       * 
60       * @param dtde the <code>DropTargetDragEvent</code> 
61       */
62  
63      void dragEnter(DropTargetDragEvent   dtde);
64  
65      /**
66       * Called when a drag operation is ongoing, while the mouse pointer is still
67       * over the operable part of the drop site for the <code>DropTarget</code>
68       * registered with this listener.
69       * 
70       * @param dtde the <code>DropTargetDragEvent</code> 
71       */
72  
73      void dragOver(DropTargetDragEvent   dtde);
74  
75      /**
76       * Called if the user has modified 
77       * the current drop gesture.
78       * <P>
79       * @param dtde the <code>DropTargetDragEvent</code>
80       */
81  
82      void dropActionChanged(DropTargetDragEvent   dtde);
83  
84      /**
85       * Called while a drag operation is ongoing, when the mouse pointer has
86       * exited the operable part of the drop site for the
87       * <code>DropTarget</code> registered with this listener.
88       * 
89       * @param dte the <code>DropTargetEvent</code> 
90       */
91  
92      void dragExit(DropTargetEvent   dte);
93  
94      /**
95       * Called when the drag operation has terminated with a drop on
96       * the operable part of the drop site for the <code>DropTarget</code>
97       * registered with this listener.  
98       * <p>
99       * This method is responsible for undertaking
100      * the transfer of the data associated with the
101      * gesture. The <code>DropTargetDropEvent</code> 
102      * provides a means to obtain a <code>Transferable</code>
103      * object that represents the data object(s) to 
104      * be transfered.<P>
105      * From this method, the <code>DropTargetListener</code>
106      * shall accept or reject the drop via the   
107      * acceptDrop(int dropAction) or rejectDrop() methods of the 
108      * <code>DropTargetDropEvent</code> parameter.
109      * <P>
110      * Subsequent to acceptDrop(), but not before,
111      * <code>DropTargetDropEvent</code>'s getTransferable()
112      * method may be invoked, and data transfer may be 
113      * performed via the returned <code>Transferable</code>'s 
114      * getTransferData() method.
115      * <P>
116      * At the completion of a drop, an implementation
117      * of this method is required to signal the success/failure
118      * of the drop by passing an appropriate
119      * <code>boolean</code> to the <code>DropTargetDropEvent</code>'s
120      * dropComplete(boolean success) method.
121      * <P>
122      * Note: The data transfer should be completed before the call  to the
123      * <code>DropTargetDropEvent</code>'s dropComplete(boolean success) method.
124      * After that, a call to the getTransferData() method of the
125      * <code>Transferable</code> returned by
126      * <code>DropTargetDropEvent.getTransferable()</code> is guaranteed to
127      * succeed only if the data transfer is local; that is, only if
128      * <code>DropTargetDropEvent.isLocalTransfer()</code> returns
129      * <code>true</code>. Otherwise, the behavior of the call is
130      * implementation-dependent.
131      * <P>
132      * @param dtde the <code>DropTargetDropEvent</code> 
133      */
134 
135     void drop(DropTargetDropEvent   dtde);
136 }
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