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;"> </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;">X</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#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