Fix nasty bug #706. See trac.
[phpeclipse.git] / net.sourceforge.phpeclipse / src / net / sourceforge / phpdt / internal / ui / dnd / DelegatingDragAdapter.java
1 /*******************************************************************************
2  * Copyright (c) 2000, 2003 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials 
4  * are made available under the terms of the Common Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/cpl-v10.html
7  * 
8  * Contributors:
9  *     IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package net.sourceforge.phpdt.internal.ui.dnd;
12
13 import java.util.ArrayList;
14 import java.util.Iterator;
15 import java.util.List;
16
17 import org.eclipse.jface.util.Assert;
18 import org.eclipse.swt.dnd.DragSource;
19 import org.eclipse.swt.dnd.DragSourceEvent;
20 import org.eclipse.swt.dnd.DragSourceListener;
21 import org.eclipse.swt.dnd.Transfer;
22 import org.eclipse.swt.dnd.TransferData;
23
24 /**
25  * A delegating drag adapter negotiates between a set of
26  * <code>TransferDragSourceListener</code>s On <code>dragStart</code> the
27  * adapter determines the listener to be used for any further <code>drag*</code>
28  * callback.
29  */
30 public class DelegatingDragAdapter implements DragSourceListener {
31
32         private TransferDragSourceListener[] fPossibleListeners;
33
34         private List fActiveListeners;
35
36         private TransferDragSourceListener fFinishListener;
37
38         public DelegatingDragAdapter(TransferDragSourceListener[] listeners) {
39                 setPossibleListeners(listeners);
40         }
41
42         protected void setPossibleListeners(TransferDragSourceListener[] listeners) {
43                 Assert.isNotNull(listeners);
44                 Assert
45                                 .isTrue(fActiveListeners == null,
46                                                 "Can only set possible listeners before drag operation has started"); //$NON-NLS-1$
47                 fPossibleListeners = listeners;
48         }
49
50         /*
51          * non Java-doc
52          * 
53          * @see DragSourceListener
54          */
55         public void dragStart(DragSourceEvent event) {
56                 fFinishListener = null;
57                 boolean saveDoit = event.doit;
58                 Object saveData = event.data;
59                 boolean doIt = false;
60                 List transfers = new ArrayList(fPossibleListeners.length);
61                 fActiveListeners = new ArrayList(fPossibleListeners.length);
62
63                 for (int i = 0; i < fPossibleListeners.length; i++) {
64                         TransferDragSourceListener listener = fPossibleListeners[i];
65                         event.doit = saveDoit;
66                         listener.dragStart(event);
67                         if (event.doit) {
68                                 transfers.add(listener.getTransfer());
69                                 fActiveListeners.add(listener);
70                         }
71                         doIt = doIt || event.doit;
72                 }
73                 if (doIt) {
74                         ((DragSource) event.widget).setTransfer((Transfer[]) transfers
75                                         .toArray(new Transfer[transfers.size()]));
76                 }
77                 event.data = saveData;
78                 event.doit = doIt;
79         }
80
81         /*
82          * non Java-doc
83          * 
84          * @see DragSourceListener
85          */
86         public void dragSetData(DragSourceEvent event) {
87                 fFinishListener = getListener(event.dataType);
88                 if (fFinishListener != null)
89                         fFinishListener.dragSetData(event);
90         }
91
92         /*
93          * non Java-doc
94          * 
95          * @see DragSourceListener
96          */
97         public void dragFinished(DragSourceEvent event) {
98                 try {
99                         if (fFinishListener != null) {
100                                 fFinishListener.dragFinished(event);
101                         } else {
102                                 // If the user presses Escape then we get a dragFinished without
103                                 // getting a dragSetData before.
104                                 fFinishListener = getListener(event.dataType);
105                                 if (fFinishListener != null)
106                                         fFinishListener.dragFinished(event);
107                         }
108                 } finally {
109                         fFinishListener = null;
110                         fActiveListeners = null;
111                 }
112         }
113
114         private TransferDragSourceListener getListener(TransferData type) {
115                 if (type == null)
116                         return null;
117
118                 for (Iterator iter = fActiveListeners.iterator(); iter.hasNext();) {
119                         TransferDragSourceListener listener = (TransferDragSourceListener) iter
120                                         .next();
121                         if (listener.getTransfer().isSupportedType(type)) {
122                                 return listener;
123                         }
124                 }
125                 return null;
126         }
127 }