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Java > Open Source Codes > org > eclipse > jface > util > DelegatingDropAdapter


1 /*******************************************************************************
2  * Copyright (c) 2000, 2007 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Eclipse Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/epl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.jface.util;
12
13 import java.util.ArrayList JavaDoc;
14 import java.util.Iterator JavaDoc;
15 import java.util.List JavaDoc;
16
17 import org.eclipse.swt.dnd.DND;
18 import org.eclipse.swt.dnd.DropTargetEvent;
19 import org.eclipse.swt.dnd.DropTargetListener;
20 import org.eclipse.swt.dnd.Transfer;
21 import org.eclipse.swt.dnd.TransferData;
22
23 /**
24  * A <code>DelegatingDropAdapter</code> is a <code>DropTargetListener</code> that
25  * maintains and delegates to a set of {@link TransferDropTargetListener}s. Each
26  * <code>TransferDropTargetListener</code> can then be implemented as if it were
27  * the DropTarget's only <code>DropTargetListener</code>.
28  * <p>
29  * On <code>dragEnter</code>, <code>dragOperationChanged</code>, <code>dragOver</code>
30  * and <code>drop</code>, a <i>current</i> listener is obtained from the set of all
31  * <code>TransferDropTargetListeners</code>. The current listener is the first listener
32  * to return <code>true</code> for
33  * {@link TransferDropTargetListener#isEnabled(DropTargetEvent)}.
34  * The current listener is forwarded all <code>DropTargetEvents</code> until some other
35  * listener becomes the current listener, or the drop terminates.
36  * </p>
37  * <p>
38  * After adding all <code>TransferDropTargetListeners</code> to the
39  * <code>DelegatingDropAdapter</code> the combined set of <code>Transfers</code> should
40  * be set in the SWT <code>DropTarget</code>. <code>#getTransfers()</code> provides the
41  * set of <code>Transfer</code> types of all <code>TransferDropTargetListeners</code>.
42  * </p>
43  * <p>
44  * The following example snippet shows a <code>DelegatingDropAdapter</code> with two
45  * <code>TransferDropTargetListeners</code>. One supports dropping resources and
46  * demonstrates how a listener can be disabled in the isEnabled method.
47  * The other listener supports text transfer.
48  * </p>
49  * <code><pre>
50  * final TreeViewer viewer = new TreeViewer(shell, SWT.NONE);
51  * DelegatingDropAdapter dropAdapter = new DelegatingDropAdapter();
52  * dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
53  * public Transfer getTransfer() {
54  * return ResourceTransfer.getInstance();
55  * }
56  * public boolean isEnabled(DropTargetEvent event) {
57  * // disable drop listener if there is no viewer selection
58  * if (viewer.getSelection().isEmpty())
59  * return false;
60  * return true;
61  * }
62  * public void dragEnter(DropTargetEvent event) {}
63  * public void dragLeave(DropTargetEvent event) {}
64  * public void dragOperationChanged(DropTargetEvent event) {}
65  * public void dragOver(DropTargetEvent event) {}
66  * public void drop(DropTargetEvent event) {
67  * if (event.data == null)
68  * return;
69  * IResource[] resources = (IResource[]) event.data;
70  * if (event.detail == DND.DROP_COPY) {
71  * // copy resources
72  * } else {
73  * // move resources
74  * }
75  *
76  * }
77  * public void dropAccept(DropTargetEvent event) {}
78  * });
79  * dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
80  * public Transfer getTransfer() {
81  * return TextTransfer.getInstance();
82  * }
83  * public boolean isEnabled(DropTargetEvent event) {
84  * return true;
85  * }
86  * public void dragEnter(DropTargetEvent event) {}
87  * public void dragLeave(DropTargetEvent event) {}
88  * public void dragOperationChanged(DropTargetEvent event) {}
89  * public void dragOver(DropTargetEvent event) {}
90  * public void drop(DropTargetEvent event) {
91  * if (event.data == null)
92  * return;
93  * System.out.println(event.data);
94  * }
95  * public void dropAccept(DropTargetEvent event) {}
96  * });
97  * viewer.addDropSupport(DND.DROP_COPY | DND.DROP_MOVE, dropAdapter.getTransfers(), dropAdapter);
98  * </pre></code>
99  * @since 3.0
100  */
101 public class DelegatingDropAdapter implements DropTargetListener {
102     private List JavaDoc listeners = new ArrayList JavaDoc();
103
104     private TransferDropTargetListener currentListener;
105
106     private int originalDropType;
107
108     /**
109      * Adds the given <code>TransferDropTargetListener</code>.
110      *
111      * @param listener the new listener
112      */
113     public void addDropTargetListener(TransferDropTargetListener listener) {
114         listeners.add(listener);
115     }
116
117     /**
118      * The cursor has entered the drop target boundaries. The current listener is
119      * updated, and <code>#dragEnter()</code> is forwarded to the current listener.
120      *
121      * @param event the drop target event
122      * @see DropTargetListener#dragEnter(DropTargetEvent)
123      */
124     public void dragEnter(DropTargetEvent event) {
125         // if (Policy.DEBUG_DRAG_DROP)
126 // System.out.println("Drag Enter: " + toString()); //$NON-NLS-1$
127 originalDropType = event.detail;
128         updateCurrentListener(event);
129     }
130
131     /**
132      * The cursor has left the drop target boundaries. The event is forwarded to the
133      * current listener.
134      *
135      * @param event the drop target event
136      * @see DropTargetListener#dragLeave(DropTargetEvent)
137      */
138     public void dragLeave(final DropTargetEvent event) {
139         // if (Policy.DEBUG_DRAG_DROP)
140 // System.out.println("Drag Leave: " + toString()); //$NON-NLS-1$
141 setCurrentListener(null, event);
142     }
143
144     /**
145      * The operation being performed has changed (usually due to the user changing
146      * a drag modifier key while dragging). Updates the current listener and forwards
147      * this event to that listener.
148      *
149      * @param event the drop target event
150      * @see DropTargetListener#dragOperationChanged(DropTargetEvent)
151      */
152     public void dragOperationChanged(final DropTargetEvent event) {
153         // if (Policy.DEBUG_DRAG_DROP)
154 // System.out.println("Drag Operation Changed to: " + event.detail); //$NON-NLS-1$
155 originalDropType = event.detail;
156         TransferDropTargetListener oldListener = getCurrentListener();
157         updateCurrentListener(event);
158         final TransferDropTargetListener newListener = getCurrentListener();
159         // only notify the current listener if it hasn't changed based on the
160 // operation change. otherwise the new listener would get a dragEnter
161 // followed by a dragOperationChanged with the exact same event.
162 if (newListener != null && newListener == oldListener) {
163             SafeRunnable.run(new SafeRunnable() {
164                 public void run() throws Exception JavaDoc {
165                     newListener.dragOperationChanged(event);
166                 }
167             });
168         }
169     }
170
171     /**
172      * The cursor is moving over the drop target. Updates the current listener and
173      * forwards this event to that listener. If no listener can handle the drag
174      * operation the <code>event.detail</code> field is set to <code>DND.DROP_NONE</code>
175      * to indicate an invalid drop.
176      *
177      * @param event the drop target event
178      * @see DropTargetListener#dragOver(DropTargetEvent)
179      */
180     public void dragOver(final DropTargetEvent event) {
181         TransferDropTargetListener oldListener = getCurrentListener();
182         updateCurrentListener(event);
183         final TransferDropTargetListener newListener = getCurrentListener();
184
185         // only notify the current listener if it hasn't changed based on the
186 // drag over. otherwise the new listener would get a dragEnter
187 // followed by a dragOver with the exact same event.
188 if (newListener != null && newListener == oldListener) {
189             SafeRunnable.run(new SafeRunnable() {
190                 public void run() throws Exception JavaDoc {
191                     newListener.dragOver(event);
192                 }
193             });
194         }
195     }
196
197     /**
198      * Forwards this event to the current listener, if there is one. Sets the
199      * current listener to <code>null</code> afterwards.
200      *
201      * @param event the drop target event
202      * @see DropTargetListener#drop(DropTargetEvent)
203      */
204     public void drop(final DropTargetEvent event) {
205         // if (Policy.DEBUG_DRAG_DROP)
206 // System.out.println("Drop: " + toString()); //$NON-NLS-1$
207 updateCurrentListener(event);
208         if (getCurrentListener() != null) {
209             SafeRunnable.run(new SafeRunnable() {
210                 public void run() throws Exception JavaDoc {
211                     getCurrentListener().drop(event);
212                 }
213             });
214         }
215         setCurrentListener(null, event);
216     }
217
218     /**
219      * Forwards this event to the current listener if there is one.
220      *
221      * @param event the drop target event
222      * @see DropTargetListener#dropAccept(DropTargetEvent)
223      */
224     public void dropAccept(final DropTargetEvent event) {
225         // if (Policy.DEBUG_DRAG_DROP)
226 // System.out.println("Drop Accept: " + toString()); //$NON-NLS-1$
227 if (getCurrentListener() != null) {
228             SafeRunnable.run(new SafeRunnable() {
229                 public void run() throws Exception JavaDoc {
230                     getCurrentListener().dropAccept(event);
231                 }
232             });
233         }
234     }
235
236     /**
237      * Returns the listener which currently handles drop events.
238      *
239      * @return the <code>TransferDropTargetListener</code> which currently
240      * handles drop events.
241      */
242     private TransferDropTargetListener getCurrentListener() {
243         return currentListener;
244     }
245
246     /**
247      * Returns the transfer data type supported by the given listener.
248      * Returns <code>null</code> if the listener does not support any of the
249      * specified data types.
250      *
251      * @param dataTypes available data types
252      * @param listener <code>TransferDropTargetListener</code> to use for testing
253      * supported data types.
254      * @return the transfer data type supported by the given listener or
255      * <code>null</code>.
256      */
257     private TransferData getSupportedTransferType(TransferData[] dataTypes,
258             TransferDropTargetListener listener) {
259         for (int i = 0; i < dataTypes.length; i++) {
260             if (listener.getTransfer().isSupportedType(dataTypes[i])) {
261                 return dataTypes[i];
262             }
263         }
264         return null;
265     }
266
267     /**
268      * Returns the combined set of <code>Transfer</code> types of all
269      * <code>TransferDropTargetListeners</code>.
270      *
271      * @return the combined set of <code>Transfer</code> types
272      */
273     public Transfer[] getTransfers() {
274         Transfer[] types = new Transfer[listeners.size()];
275         for (int i = 0; i < listeners.size(); i++) {
276             TransferDropTargetListener listener = (TransferDropTargetListener) listeners
277                     .get(i);
278             types[i] = listener.getTransfer();
279         }
280         return types;
281     }
282
283     /**
284      * Returns <code>true</code> if there are no listeners to delegate events to.
285      *
286      * @return <code>true</code> if there are no <code>TransferDropTargetListeners</code>
287      * <code>false</code> otherwise
288      */
289     public boolean isEmpty() {
290         return listeners.isEmpty();
291     }
292
293     /**
294      * Removes the given <code>TransferDropTargetListener</code>.
295      * Listeners should not be removed while a drag and drop operation is in progress.
296      *
297      * @param listener the listener to remove
298      */
299     public void removeDropTargetListener(TransferDropTargetListener listener) {
300         if (currentListener == listener) {
301             currentListener = null;
302         }
303         listeners.remove(listener);
304     }
305
306     /**
307      * Sets the current listener to <code>listener</code>. Sends the given
308      * <code>DropTargetEvent</code> if the current listener changes.
309      *
310      * @return <code>true</code> if the new listener is different than the previous
311      * <code>false</code> otherwise
312      */
313     private boolean setCurrentListener(TransferDropTargetListener listener,
314             final DropTargetEvent event) {
315         if (currentListener == listener) {
316             return false;
317         }
318         if (currentListener != null) {
319             SafeRunnable.run(new SafeRunnable() {
320                 public void run() throws Exception JavaDoc {
321                     currentListener.dragLeave(event);
322                 }
323             });
324         }
325         currentListener = listener;
326         // if (Policy.DEBUG_DRAG_DROP)
327 // System.out.println("Current drop listener: " + listener); //$NON-NLS-1$
328 if (currentListener != null) {
329             SafeRunnable.run(new SafeRunnable() {
330                 public void run() throws Exception JavaDoc {
331                     currentListener.dragEnter(event);
332                 }
333             });
334         }
335         return true;
336     }
337
338     /**
339      * Updates the current listener to one that can handle the drop. There can be many
340      * listeners and each listener may be able to handle many <code>TransferData</code>
341      * types. The first listener found that can handle a drop of one of the given
342      * <code>TransferData</code> types will be selected.
343      * If no listener can handle the drag operation the <code>event.detail</code> field
344      * is set to <code>DND.DROP_NONE</code> to indicate an invalid drop.
345      *
346      * @param event the drop target event
347      */
348     private void updateCurrentListener(DropTargetEvent event) {
349         int originalDetail = event.detail;
350         // revert the detail to the "original" drop type that the User indicated.
351 // this is necessary because the previous listener may have changed the detail
352 // to something other than what the user indicated.
353 event.detail = originalDropType;
354
355         Iterator JavaDoc iter = listeners.iterator();
356         while (iter.hasNext()) {
357             TransferDropTargetListener listener = (TransferDropTargetListener) iter
358                     .next();
359             TransferData dataType = getSupportedTransferType(event.dataTypes,
360                     listener);
361             if (dataType != null) {
362                 TransferData originalDataType = event.currentDataType;
363                 // set the data type supported by the drop listener
364 event.currentDataType = dataType;
365                 if (listener.isEnabled(event)) {
366                     // if the listener stays the same, set its previously determined
367 // event detail
368 if (!setCurrentListener(listener, event)) {
369                         event.detail = originalDetail;
370                     }
371                     return;
372                 }
373                 event.currentDataType = originalDataType;
374             }
375         }
376         setCurrentListener(null, event);
377         event.detail = DND.DROP_NONE;
378         
379         // -always- ensure that expand/scroll are on...otherwise
380 // if a valid drop target is a child of an invalid one
381 // you can't get there...
382 event.feedback = DND.FEEDBACK_EXPAND | DND.FEEDBACK_SCROLL;
383     }
384 }
385
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