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 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;"> </td> 65 * <td style="text-align: center;"> </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;"> </td> 72 * <td style="text-align: center;"> </td> 73 * <td style="text-align: center;"> </td> 74 * <td style="text-align: center;"> </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;"> </td> 83 * <td style="text-align: center;"> </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;"> </td> 90 * <td style="text-align: center;"> </td> 91 * <td style="text-align: center;"> </td> 92 * <td style="text-align: center;"> </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;"> </td> 102 * </tr> 103 * <tr> 104 * <td>ACTION_DRAG_ENDED</td> 105 * <td style="text-align: center;"> </td> 106 * <td style="text-align: center;"> </td> 107 * <td style="text-align: center;"> </td> 108 * <td style="text-align: center;"> </td> 109 * <td style="text-align: center;"> </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 boolean mEventHandlerWasCalled; 138 139 private DragEvent mNext; 140 private RuntimeException mRecycledLocation; 141 private boolean mRecycled; 142 143 private static final int MAX_RECYCLED = 10; 144 private static final Object gRecyclerLock = new Object(); 145 private static int gRecyclerUsed = 0; 146 private static DragEvent gRecyclerTop = null; 147 148 /** 149 * Action constant returned by {@link #getAction()}: Signals the start of a 150 * drag and drop operation. The View should return {@code true} from its 151 * {@link View#onDragEvent(DragEvent) onDragEvent()} handler method or 152 * {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()} listener 153 * if it can accept a drop. The onDragEvent() or onDrag() methods usually inspect the metadata 154 * from {@link #getClipDescription()} to determine if they can accept the data contained in 155 * this drag. For an operation that doesn't represent data transfer, these methods may 156 * perform other actions to determine whether or not the View should accept the data. 157 * If the View wants to indicate that it is a valid drop target, it can also react by 158 * changing its appearance. 159 * <p> 160 * Views added or becoming visible for the first time during a drag operation receive this 161 * event when they are added or becoming visible. 162 * </p> 163 * <p> 164 * A View only receives further drag events for the drag operation if it returns {@code true} 165 * in response to ACTION_DRAG_STARTED. 166 * </p> 167 * @see #ACTION_DRAG_ENDED 168 * @see #getX() 169 * @see #getY() 170 */ 171 public static final int ACTION_DRAG_STARTED = 1; 172 173 /** 174 * Action constant returned by {@link #getAction()}: Sent to a View after 175 * {@link #ACTION_DRAG_ENTERED} while the drag shadow is still within the View object's bounding 176 * box, but not within a descendant view that can accept the data. The {@link #getX()} and 177 * {@link #getY()} methods supply 178 * the X and Y position of of the drag point within the View object's bounding box. 179 * <p> 180 * A View receives an {@link #ACTION_DRAG_ENTERED} event before receiving any 181 * ACTION_DRAG_LOCATION events. 182 * </p> 183 * <p> 184 * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the 185 * drag shadow out of the View object's bounding box or into a descendant view that can accept 186 * the data. If the user moves the drag shadow back into the View object's bounding box or out 187 * of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again 188 * before receiving any more ACTION_DRAG_LOCATION events. 189 * </p> 190 * @see #ACTION_DRAG_ENTERED 191 * @see #getX() 192 * @see #getY() 193 */ 194 public static final int ACTION_DRAG_LOCATION = 2; 195 196 /** 197 * Action constant returned by {@link #getAction()}: Signals to a View that the user 198 * has released the drag shadow, and the drag point is within the bounding box of the View and 199 * not within a descendant view that can accept the data. 200 * The View should retrieve the data from the DragEvent by calling {@link #getClipData()}. 201 * The methods {@link #getX()} and {@link #getY()} return the X and Y position of the drop point 202 * within the View object's bounding box. 203 * <p> 204 * The View should return {@code true} from its {@link View#onDragEvent(DragEvent)} 205 * handler or {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()} 206 * listener if it accepted the drop, and {@code false} if it ignored the drop. 207 * </p> 208 * <p> 209 * The View can also react to this action by changing its appearance. 210 * </p> 211 * @see #getClipData() 212 * @see #getX() 213 * @see #getY() 214 */ 215 public static final int ACTION_DROP = 3; 216 217 /** 218 * Action constant returned by {@link #getAction()}: Signals to a View that the drag and drop 219 * operation has concluded. A View that changed its appearance during the operation should 220 * return to its usual drawing state in response to this event. 221 * <p> 222 * All views with listeners that returned boolean <code>true</code> for the ACTION_DRAG_STARTED 223 * event will receive the ACTION_DRAG_ENDED event even if they are not currently visible when 224 * the drag ends. Views removed during the drag operation won't receive the ACTION_DRAG_ENDED 225 * event. 226 * </p> 227 * <p> 228 * The View object can call {@link #getResult()} to see the result of the operation. 229 * If a View returned {@code true} in response to {@link #ACTION_DROP}, then 230 * getResult() returns {@code true}, otherwise it returns {@code false}. 231 * </p> 232 * @see #ACTION_DRAG_STARTED 233 * @see #getResult() 234 */ 235 public static final int ACTION_DRAG_ENDED = 4; 236 237 /** 238 * Action constant returned by {@link #getAction()}: Signals to a View that the drag point has 239 * entered the bounding box of the View. 240 * <p> 241 * If the View can accept a drop, it can react to ACTION_DRAG_ENTERED 242 * by changing its appearance in a way that tells the user that the View is the current 243 * drop target. 244 * </p> 245 * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the 246 * drag shadow out of the View object's bounding box or into a descendant view that can accept 247 * the data. If the user moves the drag shadow back into the View object's bounding box or out 248 * of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again 249 * before receiving any more ACTION_DRAG_LOCATION events. 250 * </p> 251 * @see #ACTION_DRAG_ENTERED 252 * @see #ACTION_DRAG_LOCATION 253 */ 254 public static final int ACTION_DRAG_ENTERED = 5; 255 256 /** 257 * Action constant returned by {@link #getAction()}: Signals that the user has moved the 258 * drag shadow out of the bounding box of the View or into a descendant view that can accept 259 * the data. 260 * The View can react by changing its appearance in a way that tells the user that 261 * View is no longer the immediate drop target. 262 * <p> 263 * After the system sends an ACTION_DRAG_EXITED event to the View, the View receives no more 264 * ACTION_DRAG_LOCATION events until the user drags the drag shadow back over the View. 265 * </p> 266 * 267 */ 268 public static final int ACTION_DRAG_EXITED = 6; 269 DragEvent()270 private DragEvent() { 271 } 272 init(int action, float x, float y, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result)273 private void init(int action, float x, float y, ClipDescription description, ClipData data, 274 IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result) { 275 mAction = action; 276 mX = x; 277 mY = y; 278 mClipDescription = description; 279 mClipData = data; 280 this.mDragAndDropPermissions = dragAndDropPermissions; 281 mLocalState = localState; 282 mDragResult = result; 283 } 284 obtain()285 static DragEvent obtain() { 286 return DragEvent.obtain(0, 0f, 0f, null, null, null, null, false); 287 } 288 289 /** @hide */ obtain(int action, float x, float y, Object localState, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, boolean result)290 public static DragEvent obtain(int action, float x, float y, Object localState, 291 ClipDescription description, ClipData data, 292 IDragAndDropPermissions dragAndDropPermissions, boolean result) { 293 final DragEvent ev; 294 synchronized (gRecyclerLock) { 295 if (gRecyclerTop == null) { 296 ev = new DragEvent(); 297 ev.init(action, x, y, description, data, dragAndDropPermissions, localState, 298 result); 299 return ev; 300 } 301 ev = gRecyclerTop; 302 gRecyclerTop = ev.mNext; 303 gRecyclerUsed -= 1; 304 } 305 ev.mRecycledLocation = null; 306 ev.mRecycled = false; 307 ev.mNext = null; 308 309 ev.init(action, x, y, description, data, dragAndDropPermissions, localState, result); 310 311 return ev; 312 } 313 314 /** @hide */ obtain(DragEvent source)315 public static DragEvent obtain(DragEvent source) { 316 return obtain(source.mAction, source.mX, source.mY, source.mLocalState, 317 source.mClipDescription, source.mClipData, source.mDragAndDropPermissions, 318 source.mDragResult); 319 } 320 321 /** 322 * Inspect the action value of this event. 323 * @return One of the following action constants, in the order in which they usually occur 324 * during a drag and drop operation: 325 * <ul> 326 * <li>{@link #ACTION_DRAG_STARTED}</li> 327 * <li>{@link #ACTION_DRAG_ENTERED}</li> 328 * <li>{@link #ACTION_DRAG_LOCATION}</li> 329 * <li>{@link #ACTION_DROP}</li> 330 * <li>{@link #ACTION_DRAG_EXITED}</li> 331 * <li>{@link #ACTION_DRAG_ENDED}</li> 332 * </ul> 333 */ getAction()334 public int getAction() { 335 return mAction; 336 } 337 338 /** 339 * Gets the X coordinate of the drag point. The value is only valid if the event action is 340 * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}. 341 * @return The current drag point's X coordinate 342 */ getX()343 public float getX() { 344 return mX; 345 } 346 347 /** 348 * Gets the Y coordinate of the drag point. The value is only valid if the event action is 349 * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}. 350 * @return The current drag point's Y coordinate 351 */ getY()352 public float getY() { 353 return mY; 354 } 355 356 /** 357 * Returns the {@link android.content.ClipData} object sent to the system as part of the call 358 * to 359 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 360 * startDragAndDrop()}. 361 * This method only returns valid data if the event action is {@link #ACTION_DROP}. 362 * @return The ClipData sent to the system by startDragAndDrop(). 363 */ getClipData()364 public ClipData getClipData() { 365 return mClipData; 366 } 367 368 /** 369 * Returns the {@link android.content.ClipDescription} object contained in the 370 * {@link android.content.ClipData} object sent to the system as part of the call to 371 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 372 * startDragAndDrop()}. 373 * The drag handler or listener for a View can use the metadata in this object to decide if the 374 * View can accept the dragged View object's data. 375 * <p> 376 * This method returns valid data for all event actions except for {@link #ACTION_DRAG_ENDED}. 377 * @return The ClipDescription that was part of the ClipData sent to the system by 378 * startDragAndDrop(). 379 */ getClipDescription()380 public ClipDescription getClipDescription() { 381 return mClipDescription; 382 } 383 384 /** @hide */ getDragAndDropPermissions()385 public IDragAndDropPermissions getDragAndDropPermissions() { 386 return mDragAndDropPermissions; 387 } 388 389 /** 390 * Returns the local state object sent to the system as part of the call to 391 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 392 * startDragAndDrop()}. 393 * The object is intended to provide local information about the drag and drop operation. For 394 * example, it can indicate whether the drag and drop operation is a copy or a move. 395 * <p> 396 * The local state is available only to views in the activity which has started the drag 397 * operation. In all other activities this method will return null 398 * </p> 399 * <p> 400 * This method returns valid data for all event actions except for {@link #ACTION_DRAG_ENDED}. 401 * </p> 402 * @return The local state object sent to the system by startDragAndDrop(). 403 */ getLocalState()404 public Object getLocalState() { 405 return mLocalState; 406 } 407 408 /** 409 * <p> 410 * Returns an indication of the result of the drag and drop operation. 411 * This method only returns valid data if the action type is {@link #ACTION_DRAG_ENDED}. 412 * The return value depends on what happens after the user releases the drag shadow. 413 * </p> 414 * <p> 415 * If the user releases the drag shadow on a View that can accept a drop, the system sends an 416 * {@link #ACTION_DROP} event to the View object's drag event listener. If the listener 417 * returns {@code true}, then getResult() will return {@code true}. 418 * If the listener returns {@code false}, then getResult() returns {@code false}. 419 * </p> 420 * <p> 421 * Notice that getResult() also returns {@code false} if no {@link #ACTION_DROP} is sent. This 422 * happens, for example, when the user releases the drag shadow over an area outside of the 423 * application. In this case, the system sends out {@link #ACTION_DRAG_ENDED} for the current 424 * operation, but never sends out {@link #ACTION_DROP}. 425 * </p> 426 * @return {@code true} if a drag event listener returned {@code true} in response to 427 * {@link #ACTION_DROP}. If the system did not send {@link #ACTION_DROP} before 428 * {@link #ACTION_DRAG_ENDED}, or if the listener returned {@code false} in response to 429 * {@link #ACTION_DROP}, then {@code false} is returned. 430 */ getResult()431 public boolean getResult() { 432 return mDragResult; 433 } 434 435 /** 436 * Recycle the DragEvent, to be re-used by a later caller. After calling 437 * this function you must never touch the event again. 438 * 439 * @hide 440 */ recycle()441 public final void recycle() { 442 // Ensure recycle is only called once! 443 if (TRACK_RECYCLED_LOCATION) { 444 if (mRecycledLocation != null) { 445 throw new RuntimeException(toString() + " recycled twice!", mRecycledLocation); 446 } 447 mRecycledLocation = new RuntimeException("Last recycled here"); 448 } else { 449 if (mRecycled) { 450 throw new RuntimeException(toString() + " recycled twice!"); 451 } 452 mRecycled = true; 453 } 454 455 mClipData = null; 456 mClipDescription = null; 457 mLocalState = null; 458 mEventHandlerWasCalled = false; 459 460 synchronized (gRecyclerLock) { 461 if (gRecyclerUsed < MAX_RECYCLED) { 462 gRecyclerUsed++; 463 mNext = gRecyclerTop; 464 gRecyclerTop = this; 465 } 466 } 467 } 468 469 /** 470 * Returns a string containing a concise, human-readable representation of this DragEvent 471 * object. 472 * @return A string representation of the DragEvent object. 473 */ 474 @Override toString()475 public String toString() { 476 return "DragEvent{" + Integer.toHexString(System.identityHashCode(this)) 477 + " action=" + mAction + " @ (" + mX + ", " + mY + ") desc=" + mClipDescription 478 + " data=" + mClipData + " local=" + mLocalState + " result=" + mDragResult 479 + "}"; 480 } 481 482 /* Parcelable interface */ 483 484 /** 485 * Returns information about the {@link android.os.Parcel} representation of this DragEvent 486 * object. 487 * @return Information about the {@link android.os.Parcel} representation. 488 */ describeContents()489 public int describeContents() { 490 return 0; 491 } 492 493 /** 494 * Creates a {@link android.os.Parcel} object from this DragEvent object. 495 * @param dest A {@link android.os.Parcel} object in which to put the DragEvent object. 496 * @param flags Flags to store in the Parcel. 497 */ writeToParcel(Parcel dest, int flags)498 public void writeToParcel(Parcel dest, int flags) { 499 dest.writeInt(mAction); 500 dest.writeFloat(mX); 501 dest.writeFloat(mY); 502 dest.writeInt(mDragResult ? 1 : 0); 503 if (mClipData == null) { 504 dest.writeInt(0); 505 } else { 506 dest.writeInt(1); 507 mClipData.writeToParcel(dest, flags); 508 } 509 if (mClipDescription == null) { 510 dest.writeInt(0); 511 } else { 512 dest.writeInt(1); 513 mClipDescription.writeToParcel(dest, flags); 514 } 515 if (mDragAndDropPermissions == null) { 516 dest.writeInt(0); 517 } else { 518 dest.writeInt(1); 519 dest.writeStrongBinder(mDragAndDropPermissions.asBinder()); 520 } 521 } 522 523 /** 524 * A container for creating a DragEvent from a Parcel. 525 */ 526 public static final Parcelable.Creator<DragEvent> CREATOR = 527 new Parcelable.Creator<DragEvent>() { 528 public DragEvent createFromParcel(Parcel in) { 529 DragEvent event = DragEvent.obtain(); 530 event.mAction = in.readInt(); 531 event.mX = in.readFloat(); 532 event.mY = in.readFloat(); 533 event.mDragResult = (in.readInt() != 0); 534 if (in.readInt() != 0) { 535 event.mClipData = ClipData.CREATOR.createFromParcel(in); 536 } 537 if (in.readInt() != 0) { 538 event.mClipDescription = ClipDescription.CREATOR.createFromParcel(in); 539 } 540 if (in.readInt() != 0) { 541 event.mDragAndDropPermissions = 542 IDragAndDropPermissions.Stub.asInterface(in.readStrongBinder());; 543 } 544 return event; 545 } 546 547 public DragEvent[] newArray(int size) { 548 return new DragEvent[size]; 549 } 550 }; 551 } 552