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;">X</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#getLocalState()} 116 * {@link android.view.DragEvent#describeContents()}, 117 * {@link android.view.DragEvent#writeToParcel(Parcel,int)}, and 118 * {@link android.view.DragEvent#toString()} methods always return valid data. 119 * </p> 120 * 121 * <div class="special reference"> 122 * <h3>Developer Guides</h3> 123 * <p>For a guide to implementing drag and drop features, read the 124 * <a href="{@docRoot}guide/topics/ui/drag-drop.html">Drag and Drop</a> developer guide.</p> 125 * </div> 126 */ 127 public class DragEvent implements Parcelable { 128 private static final boolean TRACK_RECYCLED_LOCATION = false; 129 130 int mAction; 131 float mX, mY; 132 ClipDescription mClipDescription; 133 ClipData mClipData; 134 IDragAndDropPermissions mDragAndDropPermissions; 135 136 Object mLocalState; 137 boolean mDragResult; 138 boolean mEventHandlerWasCalled; 139 140 private DragEvent mNext; 141 private RuntimeException mRecycledLocation; 142 private boolean mRecycled; 143 144 private static final int MAX_RECYCLED = 10; 145 private static final Object gRecyclerLock = new Object(); 146 private static int gRecyclerUsed = 0; 147 private static DragEvent gRecyclerTop = null; 148 149 /** 150 * Action constant returned by {@link #getAction()}: Signals the start of a 151 * drag and drop operation. The View should return {@code true} from its 152 * {@link View#onDragEvent(DragEvent) onDragEvent()} handler method or 153 * {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()} listener 154 * if it can accept a drop. The onDragEvent() or onDrag() methods usually inspect the metadata 155 * from {@link #getClipDescription()} to determine if they can accept the data contained in 156 * this drag. For an operation that doesn't represent data transfer, these methods may 157 * perform other actions to determine whether or not the View should accept the data. 158 * If the View wants to indicate that it is a valid drop target, it can also react by 159 * changing its appearance. 160 * <p> 161 * Views added or becoming visible for the first time during a drag operation receive this 162 * event when they are added or becoming visible. 163 * </p> 164 * <p> 165 * A View only receives further drag events for the drag operation if it returns {@code true} 166 * in response to ACTION_DRAG_STARTED. 167 * </p> 168 * @see #ACTION_DRAG_ENDED 169 * @see #getX() 170 * @see #getY() 171 */ 172 public static final int ACTION_DRAG_STARTED = 1; 173 174 /** 175 * Action constant returned by {@link #getAction()}: Sent to a View after 176 * {@link #ACTION_DRAG_ENTERED} while the drag shadow is still within the View object's bounding 177 * box, but not within a descendant view that can accept the data. The {@link #getX()} and 178 * {@link #getY()} methods supply 179 * the X and Y position of of the drag point within the View object's bounding box. 180 * <p> 181 * A View receives an {@link #ACTION_DRAG_ENTERED} event before receiving any 182 * ACTION_DRAG_LOCATION events. 183 * </p> 184 * <p> 185 * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the 186 * drag shadow out of the View object's bounding box or into a descendant view that can accept 187 * the data. If the user moves the drag shadow back into the View object's bounding box or out 188 * of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again 189 * before receiving any more ACTION_DRAG_LOCATION events. 190 * </p> 191 * @see #ACTION_DRAG_ENTERED 192 * @see #getX() 193 * @see #getY() 194 */ 195 public static final int ACTION_DRAG_LOCATION = 2; 196 197 /** 198 * Action constant returned by {@link #getAction()}: Signals to a View that the user 199 * has released the drag shadow, and the drag point is within the bounding box of the View and 200 * not within a descendant view that can accept the data. 201 * The View should retrieve the data from the DragEvent by calling {@link #getClipData()}. 202 * The methods {@link #getX()} and {@link #getY()} return the X and Y position of the drop point 203 * within the View object's bounding box. 204 * <p> 205 * The View should return {@code true} from its {@link View#onDragEvent(DragEvent)} 206 * handler or {@link View.OnDragListener#onDrag(View,DragEvent) OnDragListener.onDrag()} 207 * listener if it accepted the drop, and {@code false} if it ignored the drop. 208 * </p> 209 * <p> 210 * The View can also react to this action by changing its appearance. 211 * </p> 212 * @see #getClipData() 213 * @see #getX() 214 * @see #getY() 215 */ 216 public static final int ACTION_DROP = 3; 217 218 /** 219 * Action constant returned by {@link #getAction()}: Signals to a View that the drag and drop 220 * operation has concluded. A View that changed its appearance during the operation should 221 * return to its usual drawing state in response to this event. 222 * <p> 223 * All views with listeners that returned boolean <code>true</code> for the ACTION_DRAG_STARTED 224 * event will receive the ACTION_DRAG_ENDED event even if they are not currently visible when 225 * the drag ends. Views removed during the drag operation won't receive the ACTION_DRAG_ENDED 226 * event. 227 * </p> 228 * <p> 229 * The View object can call {@link #getResult()} to see the result of the operation. 230 * If a View returned {@code true} in response to {@link #ACTION_DROP}, then 231 * getResult() returns {@code true}, otherwise it returns {@code false}. 232 * </p> 233 * @see #ACTION_DRAG_STARTED 234 * @see #getResult() 235 */ 236 public static final int ACTION_DRAG_ENDED = 4; 237 238 /** 239 * Action constant returned by {@link #getAction()}: Signals to a View that the drag point has 240 * entered the bounding box of the View. 241 * <p> 242 * If the View can accept a drop, it can react to ACTION_DRAG_ENTERED 243 * by changing its appearance in a way that tells the user that the View is the current 244 * drop target. 245 * </p> 246 * The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the 247 * drag shadow out of the View object's bounding box or into a descendant view that can accept 248 * the data. If the user moves the drag shadow back into the View object's bounding box or out 249 * of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again 250 * before receiving any more ACTION_DRAG_LOCATION events. 251 * </p> 252 * @see #ACTION_DRAG_ENTERED 253 * @see #ACTION_DRAG_LOCATION 254 */ 255 public static final int ACTION_DRAG_ENTERED = 5; 256 257 /** 258 * Action constant returned by {@link #getAction()}: Signals that the user has moved the 259 * drag shadow out of the bounding box of the View or into a descendant view that can accept 260 * the data. 261 * The View can react by changing its appearance in a way that tells the user that 262 * View is no longer the immediate drop target. 263 * <p> 264 * After the system sends an ACTION_DRAG_EXITED event to the View, the View receives no more 265 * ACTION_DRAG_LOCATION events until the user drags the drag shadow back over the View. 266 * </p> 267 * 268 */ 269 public static final int ACTION_DRAG_EXITED = 6; 270 DragEvent()271 private DragEvent() { 272 } 273 init(int action, float x, float y, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result)274 private void init(int action, float x, float y, ClipDescription description, ClipData data, 275 IDragAndDropPermissions dragAndDropPermissions, Object localState, boolean result) { 276 mAction = action; 277 mX = x; 278 mY = y; 279 mClipDescription = description; 280 mClipData = data; 281 this.mDragAndDropPermissions = dragAndDropPermissions; 282 mLocalState = localState; 283 mDragResult = result; 284 } 285 obtain()286 static DragEvent obtain() { 287 return DragEvent.obtain(0, 0f, 0f, null, null, null, null, false); 288 } 289 290 /** @hide */ obtain(int action, float x, float y, Object localState, ClipDescription description, ClipData data, IDragAndDropPermissions dragAndDropPermissions, boolean result)291 public static DragEvent obtain(int action, float x, float y, Object localState, 292 ClipDescription description, ClipData data, 293 IDragAndDropPermissions dragAndDropPermissions, boolean result) { 294 final DragEvent ev; 295 synchronized (gRecyclerLock) { 296 if (gRecyclerTop == null) { 297 ev = new DragEvent(); 298 ev.init(action, x, y, description, data, dragAndDropPermissions, localState, 299 result); 300 return ev; 301 } 302 ev = gRecyclerTop; 303 gRecyclerTop = ev.mNext; 304 gRecyclerUsed -= 1; 305 } 306 ev.mRecycledLocation = null; 307 ev.mRecycled = false; 308 ev.mNext = null; 309 310 ev.init(action, x, y, description, data, dragAndDropPermissions, localState, result); 311 312 return ev; 313 } 314 315 /** @hide */ obtain(DragEvent source)316 public static DragEvent obtain(DragEvent source) { 317 return obtain(source.mAction, source.mX, source.mY, source.mLocalState, 318 source.mClipDescription, source.mClipData, source.mDragAndDropPermissions, 319 source.mDragResult); 320 } 321 322 /** 323 * Inspect the action value of this event. 324 * @return One of the following action constants, in the order in which they usually occur 325 * during a drag and drop operation: 326 * <ul> 327 * <li>{@link #ACTION_DRAG_STARTED}</li> 328 * <li>{@link #ACTION_DRAG_ENTERED}</li> 329 * <li>{@link #ACTION_DRAG_LOCATION}</li> 330 * <li>{@link #ACTION_DROP}</li> 331 * <li>{@link #ACTION_DRAG_EXITED}</li> 332 * <li>{@link #ACTION_DRAG_ENDED}</li> 333 * </ul> 334 */ getAction()335 public int getAction() { 336 return mAction; 337 } 338 339 /** 340 * Gets the X coordinate of the drag point. The value is only valid if the event action is 341 * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}. 342 * @return The current drag point's X coordinate 343 */ getX()344 public float getX() { 345 return mX; 346 } 347 348 /** 349 * Gets the Y coordinate of the drag point. The value is only valid if the event action is 350 * {@link #ACTION_DRAG_STARTED}, {@link #ACTION_DRAG_LOCATION} or {@link #ACTION_DROP}. 351 * @return The current drag point's Y coordinate 352 */ getY()353 public float getY() { 354 return mY; 355 } 356 357 /** 358 * Returns the {@link android.content.ClipData} object sent to the system as part of the call 359 * to 360 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 361 * startDragAndDrop()}. 362 * This method only returns valid data if the event action is {@link #ACTION_DROP}. 363 * @return The ClipData sent to the system by startDragAndDrop(). 364 */ getClipData()365 public ClipData getClipData() { 366 return mClipData; 367 } 368 369 /** 370 * Returns the {@link android.content.ClipDescription} object contained in the 371 * {@link android.content.ClipData} object sent to the system as part of the call to 372 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 373 * startDragAndDrop()}. 374 * The drag handler or listener for a View can use the metadata in this object to decide if the 375 * View can accept the dragged View object's data. 376 * <p> 377 * This method returns valid data for all event actions except for {@link #ACTION_DRAG_ENDED}. 378 * @return The ClipDescription that was part of the ClipData sent to the system by 379 * startDragAndDrop(). 380 */ getClipDescription()381 public ClipDescription getClipDescription() { 382 return mClipDescription; 383 } 384 385 /** @hide */ getDragAndDropPermissions()386 public IDragAndDropPermissions getDragAndDropPermissions() { 387 return mDragAndDropPermissions; 388 } 389 390 /** 391 * Returns the local state object sent to the system as part of the call to 392 * {@link android.view.View#startDragAndDrop(ClipData,View.DragShadowBuilder,Object,int) 393 * startDragAndDrop()}. 394 * The object is intended to provide local information about the drag and drop operation. For 395 * example, it can indicate whether the drag and drop operation is a copy or a move. 396 * <p> 397 * The local state is available only to views in the activity which has started the drag 398 * operation. In all other activities this method will return null 399 * </p> 400 * <p> 401 * This method returns valid data for all event actions. 402 * </p> 403 * @return The local state object sent to the system by startDragAndDrop(). 404 */ getLocalState()405 public Object getLocalState() { 406 return mLocalState; 407 } 408 409 /** 410 * <p> 411 * Returns an indication of the result of the drag and drop operation. 412 * This method only returns valid data if the action type is {@link #ACTION_DRAG_ENDED}. 413 * The return value depends on what happens after the user releases the drag shadow. 414 * </p> 415 * <p> 416 * If the user releases the drag shadow on a View that can accept a drop, the system sends an 417 * {@link #ACTION_DROP} event to the View object's drag event listener. If the listener 418 * returns {@code true}, then getResult() will return {@code true}. 419 * If the listener returns {@code false}, then getResult() returns {@code false}. 420 * </p> 421 * <p> 422 * Notice that getResult() also returns {@code false} if no {@link #ACTION_DROP} is sent. This 423 * happens, for example, when the user releases the drag shadow over an area outside of the 424 * application. In this case, the system sends out {@link #ACTION_DRAG_ENDED} for the current 425 * operation, but never sends out {@link #ACTION_DROP}. 426 * </p> 427 * @return {@code true} if a drag event listener returned {@code true} in response to 428 * {@link #ACTION_DROP}. If the system did not send {@link #ACTION_DROP} before 429 * {@link #ACTION_DRAG_ENDED}, or if the listener returned {@code false} in response to 430 * {@link #ACTION_DROP}, then {@code false} is returned. 431 */ getResult()432 public boolean getResult() { 433 return mDragResult; 434 } 435 436 /** 437 * Recycle the DragEvent, to be re-used by a later caller. After calling 438 * this function you must never touch the event again. 439 * 440 * @hide 441 */ recycle()442 public final void recycle() { 443 // Ensure recycle is only called once! 444 if (TRACK_RECYCLED_LOCATION) { 445 if (mRecycledLocation != null) { 446 throw new RuntimeException(toString() + " recycled twice!", mRecycledLocation); 447 } 448 mRecycledLocation = new RuntimeException("Last recycled here"); 449 } else { 450 if (mRecycled) { 451 throw new RuntimeException(toString() + " recycled twice!"); 452 } 453 mRecycled = true; 454 } 455 456 mClipData = null; 457 mClipDescription = null; 458 mLocalState = null; 459 mEventHandlerWasCalled = false; 460 461 synchronized (gRecyclerLock) { 462 if (gRecyclerUsed < MAX_RECYCLED) { 463 gRecyclerUsed++; 464 mNext = gRecyclerTop; 465 gRecyclerTop = this; 466 } 467 } 468 } 469 470 /** 471 * Returns a string containing a concise, human-readable representation of this DragEvent 472 * object. 473 * @return A string representation of the DragEvent object. 474 */ 475 @Override toString()476 public String toString() { 477 return "DragEvent{" + Integer.toHexString(System.identityHashCode(this)) 478 + " action=" + mAction + " @ (" + mX + ", " + mY + ") desc=" + mClipDescription 479 + " data=" + mClipData + " local=" + mLocalState + " result=" + mDragResult 480 + "}"; 481 } 482 483 /* Parcelable interface */ 484 485 /** 486 * Returns information about the {@link android.os.Parcel} representation of this DragEvent 487 * object. 488 * @return Information about the {@link android.os.Parcel} representation. 489 */ describeContents()490 public int describeContents() { 491 return 0; 492 } 493 494 /** 495 * Creates a {@link android.os.Parcel} object from this DragEvent object. 496 * @param dest A {@link android.os.Parcel} object in which to put the DragEvent object. 497 * @param flags Flags to store in the Parcel. 498 */ writeToParcel(Parcel dest, int flags)499 public void writeToParcel(Parcel dest, int flags) { 500 dest.writeInt(mAction); 501 dest.writeFloat(mX); 502 dest.writeFloat(mY); 503 dest.writeInt(mDragResult ? 1 : 0); 504 if (mClipData == null) { 505 dest.writeInt(0); 506 } else { 507 dest.writeInt(1); 508 mClipData.writeToParcel(dest, flags); 509 } 510 if (mClipDescription == null) { 511 dest.writeInt(0); 512 } else { 513 dest.writeInt(1); 514 mClipDescription.writeToParcel(dest, flags); 515 } 516 if (mDragAndDropPermissions == null) { 517 dest.writeInt(0); 518 } else { 519 dest.writeInt(1); 520 dest.writeStrongBinder(mDragAndDropPermissions.asBinder()); 521 } 522 } 523 524 /** 525 * A container for creating a DragEvent from a Parcel. 526 */ 527 public static final Parcelable.Creator<DragEvent> CREATOR = 528 new Parcelable.Creator<DragEvent>() { 529 public DragEvent createFromParcel(Parcel in) { 530 DragEvent event = DragEvent.obtain(); 531 event.mAction = in.readInt(); 532 event.mX = in.readFloat(); 533 event.mY = in.readFloat(); 534 event.mDragResult = (in.readInt() != 0); 535 if (in.readInt() != 0) { 536 event.mClipData = ClipData.CREATOR.createFromParcel(in); 537 } 538 if (in.readInt() != 0) { 539 event.mClipDescription = ClipDescription.CREATOR.createFromParcel(in); 540 } 541 if (in.readInt() != 0) { 542 event.mDragAndDropPermissions = 543 IDragAndDropPermissions.Stub.asInterface(in.readStrongBinder());; 544 } 545 return event; 546 } 547 548 public DragEvent[] newArray(int size) { 549 return new DragEvent[size]; 550 } 551 }; 552 } 553