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1 /*
2  * Copyright (C) 2010 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package android.view;
18 
19 import android.content.ClipData;
20 import android.content.ClipDescription;
21 import android.os.Parcel;
22 import android.os.Parcelable;
23 
24 import com.android.internal.view.IDragAndDropPermissions;
25 
26 //TODO: Improve Javadoc
27 /**
28  * Represents an event that is sent out by the system at various times during a drag and drop
29  * operation. It is a complex data structure that contains several important pieces of data about
30  * the operation and the underlying data.
31  * <p>
32  *  View objects that receive a DragEvent call {@link #getAction()}, which returns
33  *  an action type that indicates the state of the drag and drop operation. This allows a View
34  *  object to react to a change in state by changing its appearance or performing other actions.
35  *  For example, a View can react to the {@link #ACTION_DRAG_ENTERED} action type by
36  *  by changing one or more colors in its displayed image.
37  * </p>
38  * <p>
39  *  During a drag and drop operation, the system displays an image that the user drags. This image
40  *  is called a drag shadow. Several action types reflect the position of the drag shadow relative
41  *  to the View receiving the event.
42  * </p>
43  * <p>
44  *  Most methods return valid data only for certain event actions. This is summarized in the
45  *  following table. Each possible {@link #getAction()} value is listed in the first column. The
46  *  other columns indicate which method or methods return valid data for that getAction() value:
47  * </p>
48  * <table>
49  *  <tr>
50  *      <th scope="col">getAction() Value</th>
51  *      <th scope="col">getClipDescription()</th>
52  *      <th scope="col">getLocalState()</th>
53  *      <th scope="col">getX()</th>
54  *      <th scope="col">getY()</th>
55  *      <th scope="col">getClipData()</th>
56  *      <th scope="col">getResult()</th>
57  *  </tr>
58  *  <tr>
59  *      <td>ACTION_DRAG_STARTED</td>
60  *      <td style="text-align: center;">X</td>
61  *      <td style="text-align: center;">X</td>
62  *      <td style="text-align: center;">X</td>
63  *      <td style="text-align: center;">X</td>
64  *      <td style="text-align: center;">&nbsp;</td>
65  *      <td style="text-align: center;">&nbsp;</td>
66  *  </tr>
67  *  <tr>
68  *      <td>ACTION_DRAG_ENTERED</td>
69  *      <td style="text-align: center;">X</td>
70  *      <td style="text-align: center;">X</td>
71  *      <td style="text-align: center;">&nbsp;</td>
72  *      <td style="text-align: center;">&nbsp;</td>
73  *      <td style="text-align: center;">&nbsp;</td>
74  *      <td style="text-align: center;">&nbsp;</td>
75  *  </tr>
76  *  <tr>
77  *      <td>ACTION_DRAG_LOCATION</td>
78  *      <td style="text-align: center;">X</td>
79  *      <td style="text-align: center;">X</td>
80  *      <td style="text-align: center;">X</td>
81  *      <td style="text-align: center;">X</td>
82  *      <td style="text-align: center;">&nbsp;</td>
83  *      <td style="text-align: center;">&nbsp;</td>
84  *  </tr>
85  *  <tr>
86  *      <td>ACTION_DRAG_EXITED</td>
87  *      <td style="text-align: center;">X</td>
88  *      <td style="text-align: center;">X</td>
89  *      <td style="text-align: center;">&nbsp;</td>
90  *      <td style="text-align: center;">&nbsp;</td>
91  *      <td style="text-align: center;">&nbsp;</td>
92  *      <td style="text-align: center;">&nbsp;</td>
93  *  </tr>
94  *  <tr>
95  *      <td>ACTION_DROP</td>
96  *      <td style="text-align: center;">X</td>
97  *      <td style="text-align: center;">X</td>
98  *      <td style="text-align: center;">X</td>
99  *      <td style="text-align: center;">X</td>
100  *      <td style="text-align: center;">X</td>
101  *      <td style="text-align: center;">&nbsp;</td>
102  *  </tr>
103  *  <tr>
104  *      <td>ACTION_DRAG_ENDED</td>
105  *      <td style="text-align: center;">X</td>
106  *      <td style="text-align: center;">X</td>
107  *      <td style="text-align: center;">&nbsp;</td>
108  *      <td style="text-align: center;">&nbsp;</td>
109  *      <td style="text-align: center;">&nbsp;</td>
110  *      <td style="text-align: center;">X</td>
111  *  </tr>
112  * </table>
113  * <p>
114  *  The {@link android.view.DragEvent#getAction()},
115  *  {@link android.view.DragEvent#describeContents()},
116  *  {@link android.view.DragEvent#writeToParcel(Parcel,int)}, and
117  *  {@link android.view.DragEvent#toString()} methods always return valid data.
118  * </p>
119  *
120  * <div class="special reference">
121  * <h3>Developer Guides</h3>
122  * <p>For a guide to implementing drag and drop features, read the
123  * <a href="{@docRoot}guide/topics/ui/drag-drop.html">Drag and Drop</a> developer guide.</p>
124  * </div>
125  */
126 public class DragEvent implements Parcelable {
127     private static final boolean TRACK_RECYCLED_LOCATION = false;
128 
129     int mAction;
130     float mX, mY;
131     ClipDescription mClipDescription;
132     ClipData mClipData;
133     IDragAndDropPermissions mDragAndDropPermissions;
134 
135     Object mLocalState;
136     boolean mDragResult;
137 
138     private DragEvent mNext;
139     private RuntimeException mRecycledLocation;
140     private boolean mRecycled;
141 
142     private static final int MAX_RECYCLED = 10;
143     private static final Object gRecyclerLock = new Object();
144     private static int gRecyclerUsed = 0;
145     private static DragEvent gRecyclerTop = null;
146 
147     /**
148      * Action constant returned by {@link #getAction()}: Signals the start of a
149      * drag and drop operation. The View should return {@code true} from its
150      * {@link View#onDragEvent(DragEvent) onDragEvent()} handler method or
151      * {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()} listener
152      * if it can accept a drop. The onDragEvent() or onDrag() methods usually inspect the metadata
153      * from {@link #getClipDescription()} to determine if they can accept the data contained in
154      * this drag. For an operation that doesn't represent data transfer, these methods may
155      * perform other actions to determine whether or not the View should accept the drag.
156      * If the View wants to indicate that it is a valid drop target, it can also react by
157      * changing its appearance.
158      * <p>
159      * A View only receives further drag events if it returns {@code true} in response to
160      * ACTION_DRAG_STARTED.
161      * </p>
162      * @see #ACTION_DRAG_ENDED
163      * @see #getX()
164      * @see #getY()
165      */
166     public static final int ACTION_DRAG_STARTED = 1;
167 
168     /**
169      * Action constant returned by {@link #getAction()}: Sent to a View after
170      * {@link #ACTION_DRAG_ENTERED} if the drag shadow is still within the View object's bounding
171      * box. The {@link #getX()} and {@link #getY()} methods supply
172      * the X and Y position of of the drag point within the View object's bounding box.
173      * <p>
174      * A View receives an {@link #ACTION_DRAG_ENTERED} event before receiving any
175      * ACTION_DRAG_LOCATION events.
176      * </p>
177      * <p>
178      * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the
179      * drag shadow out of the View object's bounding box. If the user moves the drag shadow back
180      * into the View object's bounding box, the View receives an ACTION_DRAG_ENTERED again before
181      * receiving any more ACTION_DRAG_LOCATION events.
182      * </p>
183      * @see #ACTION_DRAG_ENTERED
184      * @see #getX()
185      * @see #getY()
186      */
187     public static final int ACTION_DRAG_LOCATION = 2;
188 
189     /**
190      * Action constant returned by {@link #getAction()}: Signals to a View that the user
191      * has released the drag shadow, and the drag point is within the bounding box of the View.
192      * The View should retrieve the data from the DragEvent by calling {@link #getClipData()}.
193      * The methods {@link #getX()} and {@link #getY()} return the X and Y position of the drop point
194      * within the View object's bounding box.
195      * <p>
196      * The View should return {@code true} from its {@link View#onDragEvent(DragEvent)}
197      * handler or {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()}
198      * listener if it accepted the drop, and {@code false} if it ignored the drop.
199      * </p>
200      * <p>
201      * The View can also react to this action by changing its appearance.
202      * </p>
203      * @see #getClipData()
204      * @see #getX()
205      * @see #getY()
206      */
207     public static final int ACTION_DROP = 3;
208 
209     /**
210      * Action constant returned by {@link #getAction()}:  Signals to a View that the drag and drop
211      * operation has concluded.  A View that changed its appearance during the operation should
212      * return to its usual drawing state in response to this event.
213      * <p>
214      * All views that received an ACTION_DRAG_STARTED event will receive the
215      * ACTION_DRAG_ENDED event even if they are not currently visible when the drag ends.
216      * </p>
217      * <p>
218      *  The View object can call {@link #getResult()} to see the result of the operation.
219      *  If a View returned {@code true} in response to {@link #ACTION_DROP}, then
220      *  getResult() returns {@code true}, otherwise it returns {@code false}.
221      * </p>
222      * @see #ACTION_DRAG_STARTED
223      * @see #getResult()
224      */
225     public static final int ACTION_DRAG_ENDED = 4;
226 
227     /**
228      * Action constant returned by {@link #getAction()}: Signals to a View that the drag point has
229      * entered the bounding box of the View.
230      * <p>
231      *  If the View can accept a drop, it can react to ACTION_DRAG_ENTERED
232      *  by changing its appearance in a way that tells the user that the View is the current
233      *  drop target.
234      * </p>
235      * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the
236      * drag shadow out of the View object's bounding box. If the user moves the drag shadow back
237      * into the View object's bounding box, the View receives an ACTION_DRAG_ENTERED again before
238      * receiving any more ACTION_DRAG_LOCATION events.
239      * </p>
240      * @see #ACTION_DRAG_ENTERED
241      * @see #ACTION_DRAG_LOCATION
242      */
243     public static final int ACTION_DRAG_ENTERED = 5;
244 
245     /**
246      * Action constant returned by {@link #getAction()}: Signals that the user has moved the
247      * drag shadow outside the bounding box of the View.
248      * The View can react by changing its appearance in a way that tells the user that
249      * View is no longer the immediate drop target.
250      * <p>
251      *  After the system sends an ACTION_DRAG_EXITED event to the View, the View receives no more
252      *  ACTION_DRAG_LOCATION events until the user drags the drag shadow back over the View.
253      * </p>
254      *
255      */
256      public static final int ACTION_DRAG_EXITED = 6;
257 
DragEvent()258     private DragEvent() {
259     }
260 
init(int action, float x, float y, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result)261     private void init(int action, float x, float y, ClipDescription description, ClipData data,
262             IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result) {
263         mAction = action;
264         mX = x;
265         mY = y;
266         mClipDescription = description;
267         mClipData = data;
268         this.mDragAndDropPermissions = dragAndDropPermissions;
269         mLocalState = localState;
270         mDragResult = result;
271     }
272 
obtain()273     static DragEvent obtain() {
274         return DragEvent.obtain(0, 0f, 0f, null, null, null, null, false);
275     }
276 
277     /** @hide */
obtain(int action, float x, float y, Object localState, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, boolean result)278     public static DragEvent obtain(int action, float x, float y, Object localState,
279             ClipDescription description, ClipData data,
280             IDragAndDropPermissions dragAndDropPermissions, boolean result) {
281         final DragEvent ev;
282         synchronized (gRecyclerLock) {
283             if (gRecyclerTop == null) {
284                 ev = new DragEvent();
285                 ev.init(action, x, y, description, data, dragAndDropPermissions, localState,
286                         result);
287                 return ev;
288             }
289             ev = gRecyclerTop;
290             gRecyclerTop = ev.mNext;
291             gRecyclerUsed -= 1;
292         }
293         ev.mRecycledLocation = null;
294         ev.mRecycled = false;
295         ev.mNext = null;
296 
297         ev.init(action, x, y, description, data, dragAndDropPermissions, localState, result);
298 
299         return ev;
300     }
301 
302     /** @hide */
obtain(DragEvent source)303     public static DragEvent obtain(DragEvent source) {
304         return obtain(source.mAction, source.mX, source.mY, source.mLocalState,
305                 source.mClipDescription, source.mClipData, source.mDragAndDropPermissions,
306                 source.mDragResult);
307     }
308 
309     /**
310      * Inspect the action value of this event.
311      * @return One of the following action constants, in the order in which they usually occur
312      * during a drag and drop operation:
313      * <ul>
314      *  <li>{@link #ACTION_DRAG_STARTED}</li>
315      *  <li>{@link #ACTION_DRAG_ENTERED}</li>
316      *  <li>{@link #ACTION_DRAG_LOCATION}</li>
317      *  <li>{@link #ACTION_DROP}</li>
318      *  <li>{@link #ACTION_DRAG_EXITED}</li>
319      *  <li>{@link #ACTION_DRAG_ENDED}</li>
320      * </ul>
321      */
getAction()322     public int getAction() {
323         return mAction;
324     }
325 
326     /**
327      * Gets the X coordinate of the drag point. The value is only valid if the event action is
328      * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}.
329      * @return The current drag point's X coordinate
330      */
getX()331     public float getX() {
332         return mX;
333     }
334 
335     /**
336      * Gets the Y coordinate of the drag point. The value is only valid if the event action is
337      * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}.
338      * @return The current drag point's Y coordinate
339      */
getY()340     public float getY() {
341         return mY;
342     }
343 
344     /**
345      * Returns the {@link android.content.ClipData} object sent to the system as part of the call
346      * to
347      * {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}.
348      * This method only returns valid data if the event action is {@link #ACTION_DROP}.
349      * @return The ClipData sent to the system by startDrag().
350      */
getClipData()351     public ClipData getClipData() {
352         return mClipData;
353     }
354 
355     /**
356      * Returns the {@link android.content.ClipDescription} object contained in the
357      * {@link android.content.ClipData} object sent to the system as part of the call to
358      * {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}.
359      * The drag handler or listener for a View can use the metadata in this object to decide if the
360      * View can accept the dragged View object's data.
361      * <p>
362      * This method returns valid data for all event actions.
363      * @return The ClipDescription that was part of the ClipData sent to the system by startDrag().
364      */
getClipDescription()365     public ClipDescription getClipDescription() {
366         return mClipDescription;
367     }
368 
369     /** @hide */
getDragAndDropPermissions()370     public IDragAndDropPermissions getDragAndDropPermissions() {
371         return mDragAndDropPermissions;
372     }
373 
374     /**
375      * Returns the local state object sent to the system as part of the call to
376      * {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}.
377      * The object is intended to provide local information about the drag and drop operation. For
378      * example, it can indicate whether the drag and drop operation is a copy or a move.
379      * <p>
380      *  This method returns valid data for all event actions.
381      * </p>
382      * @return The local state object sent to the system by startDrag().
383      */
getLocalState()384     public Object getLocalState() {
385         return mLocalState;
386     }
387 
388     /**
389      * <p>
390      * Returns an indication of the result of the drag and drop operation.
391      * This method only returns valid data if the action type is {@link #ACTION_DRAG_ENDED}.
392      * The return value depends on what happens after the user releases the drag shadow.
393      * </p>
394      * <p>
395      * If the user releases the drag shadow on a View that can accept a drop, the system sends an
396      * {@link #ACTION_DROP} event to the View object's drag event listener. If the listener
397      * returns {@code true}, then getResult() will return {@code true}.
398      * If the listener returns {@code false}, then getResult() returns {@code false}.
399      * </p>
400      * <p>
401      * Notice that getResult() also returns {@code false} if no {@link #ACTION_DROP} is sent. This
402      * happens, for example, when the user releases the drag shadow over an area outside of the
403      * application. In this case, the system sends out {@link #ACTION_DRAG_ENDED} for the current
404      * operation, but never sends out {@link #ACTION_DROP}.
405      * </p>
406      * @return {@code true} if a drag event listener returned {@code true} in response to
407      * {@link #ACTION_DROP}. If the system did not send {@link #ACTION_DROP} before
408      * {@link #ACTION_DRAG_ENDED}, or if the listener returned {@code false} in response to
409      * {@link #ACTION_DROP}, then {@code false} is returned.
410      */
getResult()411     public boolean getResult() {
412         return mDragResult;
413     }
414 
415     /**
416      * Recycle the DragEvent, to be re-used by a later caller.  After calling
417      * this function you must never touch the event again.
418      *
419      * @hide
420      */
recycle()421     public final void recycle() {
422         // Ensure recycle is only called once!
423         if (TRACK_RECYCLED_LOCATION) {
424             if (mRecycledLocation != null) {
425                 throw new RuntimeException(toString() + " recycled twice!", mRecycledLocation);
426             }
427             mRecycledLocation = new RuntimeException("Last recycled here");
428         } else {
429             if (mRecycled) {
430                 throw new RuntimeException(toString() + " recycled twice!");
431             }
432             mRecycled = true;
433         }
434 
435         mClipData = null;
436         mClipDescription = null;
437         mLocalState = null;
438 
439         synchronized (gRecyclerLock) {
440             if (gRecyclerUsed < MAX_RECYCLED) {
441                 gRecyclerUsed++;
442                 mNext = gRecyclerTop;
443                 gRecyclerTop = this;
444             }
445         }
446     }
447 
448     /**
449      * Returns a string containing a concise, human-readable representation of this DragEvent
450      * object.
451      * @return A string representation of the DragEvent object.
452      */
453     @Override
toString()454     public String toString() {
455         return "DragEvent{" + Integer.toHexString(System.identityHashCode(this))
456         + " action=" + mAction + " @ (" + mX + ", " + mY + ") desc=" + mClipDescription
457         + " data=" + mClipData + " local=" + mLocalState + " result=" + mDragResult
458         + "}";
459     }
460 
461     /* Parcelable interface */
462 
463     /**
464      * Returns information about the {@link android.os.Parcel} representation of this DragEvent
465      * object.
466      * @return Information about the {@link android.os.Parcel} representation.
467      */
describeContents()468     public int describeContents() {
469         return 0;
470     }
471 
472     /**
473      * Creates a {@link android.os.Parcel} object from this DragEvent object.
474      * @param dest A {@link android.os.Parcel} object in which to put the DragEvent object.
475      * @param flags Flags to store in the Parcel.
476      */
writeToParcel(Parcel dest, int flags)477     public void writeToParcel(Parcel dest, int flags) {
478         dest.writeInt(mAction);
479         dest.writeFloat(mX);
480         dest.writeFloat(mY);
481         dest.writeInt(mDragResult ? 1 : 0);
482         if (mClipData == null) {
483             dest.writeInt(0);
484         } else {
485             dest.writeInt(1);
486             mClipData.writeToParcel(dest, flags);
487         }
488         if (mClipDescription == null) {
489             dest.writeInt(0);
490         } else {
491             dest.writeInt(1);
492             mClipDescription.writeToParcel(dest, flags);
493         }
494         if (mDragAndDropPermissions == null) {
495             dest.writeInt(0);
496         } else {
497             dest.writeInt(1);
498             dest.writeStrongBinder(mDragAndDropPermissions.asBinder());
499         }
500     }
501 
502     /**
503      * A container for creating a DragEvent from a Parcel.
504      */
505     public static final Parcelable.Creator<DragEvent> CREATOR =
506         new Parcelable.Creator<DragEvent>() {
507         public DragEvent createFromParcel(Parcel in) {
508             DragEvent event = DragEvent.obtain();
509             event.mAction = in.readInt();
510             event.mX = in.readFloat();
511             event.mY = in.readFloat();
512             event.mDragResult = (in.readInt() != 0);
513             if (in.readInt() != 0) {
514                 event.mClipData = ClipData.CREATOR.createFromParcel(in);
515             }
516             if (in.readInt() != 0) {
517                 event.mClipDescription = ClipDescription.CREATOR.createFromParcel(in);
518             }
519             if (in.readInt() != 0) {
520                 event.mDragAndDropPermissions =
521                         IDragAndDropPermissions.Stub.asInterface(in.readStrongBinder());;
522             }
523             return event;
524         }
525 
526         public DragEvent[] newArray(int size) {
527             return new DragEvent[size];
528         }
529     };
530 }
531