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