BroadcastReceiver.java revision f013e1afd1e68af5e3b868c26a653bbfb39538f8
1/* 2 * Copyright (C) 2006 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 17package android.content; 18 19import android.os.Bundle; 20import android.util.Log; 21 22/** 23 * Base class for code that will receive intents sent by sendBroadcast(). 24 * You can either dynamically register an instance of this class with 25 * {@link Context#registerReceiver Context.registerReceiver()} 26 * or statically publish an implementation through the 27 * {@link android.R.styleable#AndroidManifestReceiver <receiver>} 28 * tag in your <code>AndroidManifest.xml</code>. <em><strong>Note:</strong></em> 29 * If registering a receiver in your 30 * {@link android.app.Activity#onResume() Activity.onResume()} 31 * implementation, you should unregister it in 32 * {@link android.app.Activity#onPause() Activity.onPause()}. 33 * (You won't receive intents when paused, 34 * and this will cut down on unnecessary system overhead). Do not unregister in 35 * {@link android.app.Activity#onSaveInstanceState(android.os.Bundle) Activity.onSaveInstanceState()}, 36 * because this won't be called if the user moves back in the history 37 * stack. 38 * 39 * <p>There are two major classes of broadcasts that can be received:</p> 40 * <ul> 41 * <li> <b>Normal broadcasts</b> (sent with {@link Context#sendBroadcast(Intent) 42 * Context.sendBroadcast}) are completely asynchronous. All receivers of the 43 * broadcast are run, in an undefined order, often at the same time. This is 44 * more efficient, but means that receivers can not use the result or abort 45 * APIs included here. 46 * <li> <b>Ordered broadcasts</b> (sent with {@link Context#sendOrderedBroadcast(Intent, String) 47 * Context.sendOrderedBroadcast}) are delivered to one receiver at a time. 48 * As each receiver executes in turn, it can propagate a result to the next 49 * receiver, or it can completely abort the broadcast so that it won't be passed 50 * to other receivers. The order receivers runs in can be controlled with the 51 * {@link android.R.styleable#AndroidManifestIntentFilter_priority 52 * android:priority} attribute of the matching intent-filter; receivers with 53 * the same priority will be run in an arbitrary order. 54 * </ul> 55 * 56 * <p>Even in the case of normal broadcasts, the system may in some 57 * situations revert to delivering the broadcast one receiver at a time. In 58 * particular, for receivers that may require the creation of a process, only 59 * one will be run at a time to avoid overloading the system with new processes. 60 * In this situation, however, the non-ordered semantics hold: these receivers 61 * can not return results or abort their broadcast.</p> 62 * 63 * <p>Note that, although the Intent class is used for sending and receiving 64 * these broadcasts, the Intent broadcast mechanism here is completely separate 65 * from Intents that are used to start Activities with 66 * {@link Context#startActivity Context.startActivity()}. 67 * There is no way for an BroadcastReceiver 68 * to see or capture Intents used with startActivity(); likewise, when 69 * you broadcast an Intent, you will never find or start an Activity. 70 * These two operations are semantically very different: starting an 71 * Activity with an Intent is a foreground operation that modifies what the 72 * user is currently interacting with; broadcasting an Intent is a background 73 * operation that the user is not normally aware of. 74 * 75 * <p>The BroadcastReceiver class (when launched as a component through 76 * a manifest's {@link android.R.styleable#AndroidManifestReceiver <receiver>} 77 * tag) is an important part of an 78 * <a href="{@docRoot}intro/lifecycle.html">application's overall lifecycle</a>.</p> 79 * 80 * <p>Topics covered here: 81 * <ol> 82 * <li><a href="#ReceiverLifecycle">Receiver Lifecycle</a> 83 * <li><a href="#Permissions">Permissions</a> 84 * <li><a href="#ProcessLifecycle">Process Lifecycle</a> 85 * </ol> 86 * 87 * <a name="ReceiverLifecycle"></a> 88 * <h3>Receiver Lifecycle</h3> 89 * 90 * <p>A BroadcastReceiver object is only valid for the duration of the call 91 * to {@link #onReceive}. Once your code returns from this function, 92 * the system considers the object to be finished and no longer active. 93 * 94 * <p>This has important repercussions to what you can do in an 95 * {@link #onReceive} implementation: anything that requires asynchronous 96 * operation is not available, because you will need to return from the 97 * function to handle the asynchronous operation, but at that point the 98 * BroadcastReceiver is no longer active and thus the system is free to kill 99 * its process before the asynchronous operation completes. 100 * 101 * <p>In particular, you may <i>not</i> show a dialog or bind to a service from 102 * within an BroadcastReceiver. For the former, you should instead use the 103 * {@link android.app.NotificationManager} API. For the latter, you can 104 * use {@link android.content.Context#startService Context.startService()} to 105 * send a command to the service. 106 * 107 * <a name="Permissions"></a> 108 * <h3>Permissions</h3> 109 * 110 * <p>Access permissions can be enforced by either the sender or receiver 111 * of an Intent. 112 * 113 * <p>To enforce a permission when sending, you supply a non-null 114 * <var>permission</var> argument to 115 * {@link Context#sendBroadcast(Intent, String)} or 116 * {@link Context#sendOrderedBroadcast(Intent, String, BroadcastReceiver, android.os.Handler, int, String, Bundle)}. 117 * Only receivers who have been granted this permission 118 * (by requesting it with the 119 * {@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>} 120 * tag in their <code>AndroidManifest.xml</code>) will be able to receive 121 * the broadcast. 122 * 123 * <p>To enforce a permission when receiving, you supply a non-null 124 * <var>permission</var> when registering your receiver -- either when calling 125 * {@link Context#registerReceiver(BroadcastReceiver, IntentFilter, String, android.os.Handler)} 126 * or in the static 127 * {@link android.R.styleable#AndroidManifestReceiver <receiver>} 128 * tag in your <code>AndroidManifest.xml</code>. Only broadcasters who have 129 * been granted this permission (by requesting it with the 130 * {@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>} 131 * tag in their <code>AndroidManifest.xml</code>) will be able to send an 132 * Intent to the receiver. 133 * 134 * <p>See the <a href="{@docRoot}devel/security.html">Security Model</a> 135 * document for more information on permissions and security in general. 136 * 137 * <a name="ProcessLifecycle"></a> 138 * <h3>Process Lifecycle</h3> 139 * 140 * <p>A process that is currently executing an BroadcastReceiver (that is, 141 * currently running the code in its {@link #onReceive} method) is 142 * considered to be a foreground process and will be kept running by the 143 * system except under cases of extreme memory pressure. 144 * 145 * <p>Once you return from onReceive(), the BroadcastReceiver is no longer 146 * active, and its hosting process is only as important as any other application 147 * components that are running in it. This is especially important because if 148 * that process was only hosting the BroadcastReceiver (a common case for 149 * applications that the user has never or not recently interacted with), then 150 * upon returning from onReceive() the system will consider its process 151 * to be empty and aggressively kill it so that resources are available for other 152 * more important processes. 153 * 154 * <p>This means that for longer-running operations you will often use 155 * a {@link android.app.Service} in conjunction with an BroadcastReceiver to keep 156 * the containing process active for the entire time of your operation. 157 */ 158public abstract class BroadcastReceiver { 159 public BroadcastReceiver() { 160 } 161 162 /** 163 * This method is called when the BroadcastReceiver is receiving an Intent 164 * broadcast. During this time you can use the other methods on 165 * BroadcastReceiver to view/modify the current result values. The function 166 * is normally called from the main thread of its process, so you should 167 * never perform long-running operations in it (there is a timeout of 168 * 10 seconds that the system allows before considering the receiver to 169 * be blocked and a candidate to be killed). You cannot launch a popup dialog 170 * in your implementation of onReceive(). 171 * 172 * <p><b>If this BroadcastReceiver was launched through a <receiver> tag, 173 * then the object is no longer alive after returning from this 174 * function.</b> This means you should not perform any operations that 175 * return a result to you asynchronously -- in particular, for interacting 176 * with services, you should use 177 * {@link Context#startService(Intent)} instead of 178 * {@link Context#bindService(Intent, ServiceConnection, int)}. 179 * 180 * @param context The Context in which the receiver is running. 181 * @param intent The Intent being received. 182 */ 183 public abstract void onReceive(Context context, Intent intent); 184 185 /** 186 * Change the current result code of this broadcast; only works with 187 * broadcasts sent through 188 * {@link Context#sendOrderedBroadcast(Intent, String) 189 * Context.sendOrderedBroadcast}. Often uses the 190 * Activity {@link android.app.Activity#RESULT_CANCELED} and 191 * {@link android.app.Activity#RESULT_OK} constants, though the 192 * actual meaning of this value is ultimately up to the broadcaster. 193 * 194 * <p><strong>This method does not work with non-ordered broadcasts such 195 * as those sent with {@link Context#sendBroadcast(Intent) 196 * Context.sendBroadcast}</strong></p> 197 * 198 * @param code The new result code. 199 * 200 * @see #setResult(int, String, Bundle) 201 */ 202 public final void setResultCode(int code) { 203 checkSynchronousHint(); 204 mResultCode = code; 205 } 206 207 /** 208 * Retrieve the current result code, as set by the previous receiver. 209 * 210 * @return int The current result code. 211 */ 212 public final int getResultCode() { 213 return mResultCode; 214 } 215 216 /** 217 * Change the current result data of this broadcast; only works with 218 * broadcasts sent through 219 * {@link Context#sendOrderedBroadcast(Intent, String) 220 * Context.sendOrderedBroadcast}. This is an arbitrary 221 * string whose interpretation is up to the broadcaster. 222 * 223 * <p><strong>This method does not work with non-ordered broadcasts such 224 * as those sent with {@link Context#sendBroadcast(Intent) 225 * Context.sendBroadcast}</strong></p> 226 * 227 * @param data The new result data; may be null. 228 * 229 * @see #setResult(int, String, Bundle) 230 */ 231 public final void setResultData(String data) { 232 checkSynchronousHint(); 233 mResultData = data; 234 } 235 236 /** 237 * Retrieve the current result data, as set by the previous receiver. 238 * Often this is null. 239 * 240 * @return String The current result data; may be null. 241 */ 242 public final String getResultData() { 243 return mResultData; 244 } 245 246 /** 247 * Change the current result extras of this broadcast; only works with 248 * broadcasts sent through 249 * {@link Context#sendOrderedBroadcast(Intent, String) 250 * Context.sendOrderedBroadcast}. This is a Bundle 251 * holding arbitrary data, whose interpretation is up to the 252 * broadcaster. Can be set to null. Calling this method completely 253 * replaces the current map (if any). 254 * 255 * <p><strong>This method does not work with non-ordered broadcasts such 256 * as those sent with {@link Context#sendBroadcast(Intent) 257 * Context.sendBroadcast}</strong></p> 258 * 259 * @param extras The new extra data map; may be null. 260 * 261 * @see #setResult(int, String, Bundle) 262 */ 263 public final void setResultExtras(Bundle extras) { 264 checkSynchronousHint(); 265 mResultExtras = extras; 266 } 267 268 /** 269 * Retrieve the current result extra data, as set by the previous receiver. 270 * Any changes you make to the returned Map will be propagated to the next 271 * receiver. 272 * 273 * @param makeMap If true then a new empty Map will be made for you if the 274 * current Map is null; if false you should be prepared to 275 * receive a null Map. 276 * 277 * @return Map The current extras map. 278 */ 279 public final Bundle getResultExtras(boolean makeMap) { 280 Bundle e = mResultExtras; 281 if (!makeMap) return e; 282 if (e == null) mResultExtras = e = new Bundle(); 283 return e; 284 } 285 286 /** 287 * Change all of the result data returned from this broadcasts; only works 288 * with broadcasts sent through 289 * {@link Context#sendOrderedBroadcast(Intent, String) 290 * Context.sendOrderedBroadcast}. All current result data is replaced 291 * by the value given to this method. 292 * 293 * <p><strong>This method does not work with non-ordered broadcasts such 294 * as those sent with {@link Context#sendBroadcast(Intent) 295 * Context.sendBroadcast}</strong></p> 296 * 297 * @param code The new result code. Often uses the 298 * Activity {@link android.app.Activity#RESULT_CANCELED} and 299 * {@link android.app.Activity#RESULT_OK} constants, though the 300 * actual meaning of this value is ultimately up to the broadcaster. 301 * @param data The new result data. This is an arbitrary 302 * string whose interpretation is up to the broadcaster; may be null. 303 * @param extras The new extra data map. This is a Bundle 304 * holding arbitrary data, whose interpretation is up to the 305 * broadcaster. Can be set to null. This completely 306 * replaces the current map (if any). 307 */ 308 public final void setResult(int code, String data, Bundle extras) { 309 checkSynchronousHint(); 310 mResultCode = code; 311 mResultData = data; 312 mResultExtras = extras; 313 } 314 315 /** 316 * Returns the flag indicating whether or not this receiver should 317 * abort the current broadcast. 318 * 319 * @return True if the broadcast should be aborted. 320 */ 321 public final boolean getAbortBroadcast() { 322 return mAbortBroadcast; 323 } 324 325 /** 326 * Sets the flag indicating that this receiver should abort the 327 * current broadcast; only works with broadcasts sent through 328 * {@link Context#sendOrderedBroadcast(Intent, String) 329 * Context.sendOrderedBroadcast}. This will prevent 330 * any other broadcast receivers from receiving the broadcast. It will still 331 * call {@link #onReceive} of the BroadcastReceiver that the caller of 332 * {@link Context#sendOrderedBroadcast(Intent, String) 333 * Context.sendOrderedBroadcast} passed in. 334 * 335 * <p><strong>This method does not work with non-ordered broadcasts such 336 * as those sent with {@link Context#sendBroadcast(Intent) 337 * Context.sendBroadcast}</strong></p> 338 */ 339 public final void abortBroadcast() { 340 checkSynchronousHint(); 341 mAbortBroadcast = true; 342 } 343 344 /** 345 * Clears the flag indicating that this receiver should abort the current 346 * broadcast. 347 */ 348 public final void clearAbortBroadcast() { 349 mAbortBroadcast = false; 350 } 351 352 /** 353 * For internal use, sets the hint about whether this BroadcastReceiver is 354 * running in ordered mode. 355 */ 356 public final void setOrderedHint(boolean isOrdered) { 357 mOrderedHint = isOrdered; 358 } 359 360 /** 361 * Control inclusion of debugging help for mismatched 362 * calls to {@ Context#registerReceiver(BroadcastReceiver, IntentFilter) 363 * Context.registerReceiver()}. 364 * If called with true, before given to registerReceiver(), then the 365 * callstack of the following {@link Context#unregisterReceiver(BroadcastReceiver) 366 * Context.unregisterReceiver()} call is retained, to be printed if a later 367 * incorrect unregister call is made. Note that doing this requires retaining 368 * information about the BroadcastReceiver for the lifetime of the app, 369 * resulting in a leak -- this should only be used for debugging. 370 */ 371 public final void setDebugUnregister(boolean debug) { 372 mDebugUnregister = debug; 373 } 374 375 /** 376 * Return the last value given to {@link #setDebugUnregister}. 377 */ 378 public final boolean getDebugUnregister() { 379 return mDebugUnregister; 380 } 381 382 void checkSynchronousHint() { 383 if (mOrderedHint) { 384 return; 385 } 386 RuntimeException e = new RuntimeException( 387 "BroadcastReceiver trying to return result during a non-ordered broadcast"); 388 e.fillInStackTrace(); 389 Log.e("BroadcastReceiver", e.getMessage(), e); 390 } 391 392 private int mResultCode; 393 private String mResultData; 394 private Bundle mResultExtras; 395 private boolean mAbortBroadcast; 396 private boolean mDebugUnregister; 397 private boolean mOrderedHint; 398} 399 400