Android example source code file (BroadcastReceiver.java)
The BroadcastReceiver.java Android example source code/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.content;
import android.app.ActivityManagerNative;
import android.app.IActivityManager;
import android.os.Bundle;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;
/**
* Base class for code that will receive intents sent by sendBroadcast().
* You can either dynamically register an instance of this class with
* {@link Context#registerReceiver Context.registerReceiver()}
* or statically publish an implementation through the
* {@link android.R.styleable#AndroidManifestReceiver <receiver>}
* tag in your <code>AndroidManifest.xml. Note:
* If registering a receiver in your
* {@link android.app.Activity#onResume() Activity.onResume()}
* implementation, you should unregister it in
* {@link android.app.Activity#onPause() Activity.onPause()}.
* (You won't receive intents when paused,
* and this will cut down on unnecessary system overhead). Do not unregister in
* {@link android.app.Activity#onSaveInstanceState(android.os.Bundle) Activity.onSaveInstanceState()},
* because this won't be called if the user moves back in the history
* stack.
*
* <p>There are two major classes of broadcasts that can be received:
* <ul>
* <li> Normal broadcasts (sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}) are completely asynchronous. All receivers of the
* broadcast are run in an undefined order, often at the same time. This is
* more efficient, but means that receivers cannot use the result or abort
* APIs included here.
* <li> Ordered broadcasts (sent with {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}) are delivered to one receiver at a time.
* As each receiver executes in turn, it can propagate a result to the next
* receiver, or it can completely abort the broadcast so that it won't be passed
* to other receivers. The order receivers run in can be controlled with the
* {@link android.R.styleable#AndroidManifestIntentFilter_priority
* android:priority} attribute of the matching intent-filter; receivers with
* the same priority will be run in an arbitrary order.
* </ul>
*
* <p>Even in the case of normal broadcasts, the system may in some
* situations revert to delivering the broadcast one receiver at a time. In
* particular, for receivers that may require the creation of a process, only
* one will be run at a time to avoid overloading the system with new processes.
* In this situation, however, the non-ordered semantics hold: these receivers still
* cannot return results or abort their broadcast.</p>
*
* <p>Note that, although the Intent class is used for sending and receiving
* these broadcasts, the Intent broadcast mechanism here is completely separate
* from Intents that are used to start Activities with
* {@link Context#startActivity Context.startActivity()}.
* There is no way for a BroadcastReceiver
* to see or capture Intents used with startActivity(); likewise, when
* you broadcast an Intent, you will never find or start an Activity.
* These two operations are semantically very different: starting an
* Activity with an Intent is a foreground operation that modifies what the
* user is currently interacting with; broadcasting an Intent is a background
* operation that the user is not normally aware of.
*
* <p>The BroadcastReceiver class (when launched as a component through
* a manifest's {@link android.R.styleable#AndroidManifestReceiver <receiver>}
* tag) is an important part of an
* <a href="{@docRoot}guide/topics/fundamentals.html#lcycles">application's overall lifecycle.
*
* <p>Topics covered here:
* <ol>
* <li>Receiver Lifecycle
* <li>Permissions
* <li>Process Lifecycle
* </ol>
*
* <a name="ReceiverLifecycle">
* <h3>Receiver Lifecycle
*
* <p>A BroadcastReceiver object is only valid for the duration of the call
* to {@link #onReceive}. Once your code returns from this function,
* the system considers the object to be finished and no longer active.
*
* <p>This has important repercussions to what you can do in an
* {@link #onReceive} implementation: anything that requires asynchronous
* operation is not available, because you will need to return from the
* function to handle the asynchronous operation, but at that point the
* BroadcastReceiver is no longer active and thus the system is free to kill
* its process before the asynchronous operation completes.
*
* <p>In particular, you may not show a dialog or bind to a service from
* within a BroadcastReceiver. For the former, you should instead use the
* {@link android.app.NotificationManager} API. For the latter, you can
* use {@link android.content.Context#startService Context.startService()} to
* send a command to the service.
*
* <a name="Permissions">
* <h3>Permissions
*
* <p>Access permissions can be enforced by either the sender or receiver
* of an Intent.
*
* <p>To enforce a permission when sending, you supply a non-null
* <var>permission argument to
* {@link Context#sendBroadcast(Intent, String)} or
* {@link Context#sendOrderedBroadcast(Intent, String, BroadcastReceiver, android.os.Handler, int, String, Bundle)}.
* Only receivers who have been granted this permission
* (by requesting it with the
* {@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>}
* tag in their <code>AndroidManifest.xml) will be able to receive
* the broadcast.
*
* <p>To enforce a permission when receiving, you supply a non-null
* <var>permission when registering your receiver -- either when calling
* {@link Context#registerReceiver(BroadcastReceiver, IntentFilter, String, android.os.Handler)}
* or in the static
* {@link android.R.styleable#AndroidManifestReceiver <receiver>}
* tag in your <code>AndroidManifest.xml. Only broadcasters who have
* been granted this permission (by requesting it with the
* {@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>}
* tag in their <code>AndroidManifest.xml) will be able to send an
* Intent to the receiver.
*
* <p>See the Security and Permissions
* document for more information on permissions and security in general.
*
* <a name="ProcessLifecycle">
* <h3>Process Lifecycle
*
* <p>A process that is currently executing a BroadcastReceiver (that is,
* currently running the code in its {@link #onReceive} method) is
* considered to be a foreground process and will be kept running by the
* system except under cases of extreme memory pressure.
*
* <p>Once you return from onReceive(), the BroadcastReceiver is no longer
* active, and its hosting process is only as important as any other application
* components that are running in it. This is especially important because if
* that process was only hosting the BroadcastReceiver (a common case for
* applications that the user has never or not recently interacted with), then
* upon returning from onReceive() the system will consider its process
* to be empty and aggressively kill it so that resources are available for other
* more important processes.
*
* <p>This means that for longer-running operations you will often use
* a {@link android.app.Service} in conjunction with a BroadcastReceiver to keep
* the containing process active for the entire time of your operation.
*/
public abstract class BroadcastReceiver {
public BroadcastReceiver() {
}
/**
* This method is called when the BroadcastReceiver is receiving an Intent
* broadcast. During this time you can use the other methods on
* BroadcastReceiver to view/modify the current result values. The function
* is normally called within the main thread of its process, so you should
* never perform long-running operations in it (there is a timeout of
* 10 seconds that the system allows before considering the receiver to
* be blocked and a candidate to be killed). You cannot launch a popup dialog
* in your implementation of onReceive().
*
* <p>If this BroadcastReceiver was launched through a <receiver> tag,
* then the object is no longer alive after returning from this
* function.</b> This means you should not perform any operations that
* return a result to you asynchronously -- in particular, for interacting
* with services, you should use
* {@link Context#startService(Intent)} instead of
* {@link Context#bindService(Intent, ServiceConnection, int)}. If you wish
* to interact with a service that is already running, you can use
* {@link #peekService}.
*
* <p>The Intent filters used in {@link android.content.Context#registerReceiver}
* and in application manifests are <em>not guaranteed to be exclusive. They
* are hints to the operating system about how to find suitable recipients. It is
* possible for senders to force delivery to specific recipients, bypassing filter
* resolution. For this reason, {@link #onReceive(Context, Intent) onReceive()}
* implementations should respond only to known actions, ignoring any unexpected
* Intents that they may receive.
*
* @param context The Context in which the receiver is running.
* @param intent The Intent being received.
*/
public abstract void onReceive(Context context, Intent intent);
/**
* Provide a binder to an already-running service. This method is synchronous
* and will not start the target service if it is not present, so it is safe
* to call from {@link #onReceive}.
*
* @param myContext The Context that had been passed to {@link #onReceive(Context, Intent)}
* @param service The Intent indicating the service you wish to use. See {@link
* Context#startService(Intent)} for more information.
*/
public IBinder peekService(Context myContext, Intent service) {
IActivityManager am = ActivityManagerNative.getDefault();
IBinder binder = null;
try {
binder = am.peekService(service, service.resolveTypeIfNeeded(
myContext.getContentResolver()));
} catch (RemoteException e) {
}
return binder;
}
/**
* Change the current result code of this broadcast; only works with
* broadcasts sent through
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}. Often uses the
* Activity {@link android.app.Activity#RESULT_CANCELED} and
* {@link android.app.Activity#RESULT_OK} constants, though the
* actual meaning of this value is ultimately up to the broadcaster.
*
* <p>This method does not work with non-ordered broadcasts such
* as those sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}</strong>
*
* @param code The new result code.
*
* @see #setResult(int, String, Bundle)
*/
public final void setResultCode(int code) {
checkSynchronousHint();
mResultCode = code;
}
/**
* Retrieve the current result code, as set by the previous receiver.
*
* @return int The current result code.
*/
public final int getResultCode() {
return mResultCode;
}
/**
* Change the current result data of this broadcast; only works with
* broadcasts sent through
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}. This is an arbitrary
* string whose interpretation is up to the broadcaster.
*
* <p>This method does not work with non-ordered broadcasts such
* as those sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}</strong>
*
* @param data The new result data; may be null.
*
* @see #setResult(int, String, Bundle)
*/
public final void setResultData(String data) {
checkSynchronousHint();
mResultData = data;
}
/**
* Retrieve the current result data, as set by the previous receiver.
* Often this is null.
*
* @return String The current result data; may be null.
*/
public final String getResultData() {
return mResultData;
}
/**
* Change the current result extras of this broadcast; only works with
* broadcasts sent through
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}. This is a Bundle
* holding arbitrary data, whose interpretation is up to the
* broadcaster. Can be set to null. Calling this method completely
* replaces the current map (if any).
*
* <p>This method does not work with non-ordered broadcasts such
* as those sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}</strong>
*
* @param extras The new extra data map; may be null.
*
* @see #setResult(int, String, Bundle)
*/
public final void setResultExtras(Bundle extras) {
checkSynchronousHint();
mResultExtras = extras;
}
/**
* Retrieve the current result extra data, as set by the previous receiver.
* Any changes you make to the returned Map will be propagated to the next
* receiver.
*
* @param makeMap If true then a new empty Map will be made for you if the
* current Map is null; if false you should be prepared to
* receive a null Map.
*
* @return Map The current extras map.
*/
public final Bundle getResultExtras(boolean makeMap) {
Bundle e = mResultExtras;
if (!makeMap) return e;
if (e == null) mResultExtras = e = new Bundle();
return e;
}
/**
* Change all of the result data returned from this broadcasts; only works
* with broadcasts sent through
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}. All current result data is replaced
* by the value given to this method.
*
* <p>This method does not work with non-ordered broadcasts such
* as those sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}</strong>
*
* @param code The new result code. Often uses the
* Activity {@link android.app.Activity#RESULT_CANCELED} and
* {@link android.app.Activity#RESULT_OK} constants, though the
* actual meaning of this value is ultimately up to the broadcaster.
* @param data The new result data. This is an arbitrary
* string whose interpretation is up to the broadcaster; may be null.
* @param extras The new extra data map. This is a Bundle
* holding arbitrary data, whose interpretation is up to the
* broadcaster. Can be set to null. This completely
* replaces the current map (if any).
*/
public final void setResult(int code, String data, Bundle extras) {
checkSynchronousHint();
mResultCode = code;
mResultData = data;
mResultExtras = extras;
}
/**
* Returns the flag indicating whether or not this receiver should
* abort the current broadcast.
*
* @return True if the broadcast should be aborted.
*/
public final boolean getAbortBroadcast() {
return mAbortBroadcast;
}
/**
* Sets the flag indicating that this receiver should abort the
* current broadcast; only works with broadcasts sent through
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast}. This will prevent
* any other broadcast receivers from receiving the broadcast. It will still
* call {@link #onReceive} of the BroadcastReceiver that the caller of
* {@link Context#sendOrderedBroadcast(Intent, String)
* Context.sendOrderedBroadcast} passed in.
*
* <p>This method does not work with non-ordered broadcasts such
* as those sent with {@link Context#sendBroadcast(Intent)
* Context.sendBroadcast}</strong>
*/
public final void abortBroadcast() {
checkSynchronousHint();
mAbortBroadcast = true;
}
/**
* Clears the flag indicating that this receiver should abort the current
* broadcast.
*/
public final void clearAbortBroadcast() {
mAbortBroadcast = false;
}
/**
* Returns true if the receiver is currently processing an ordered
* broadcast.
*/
public final boolean isOrderedBroadcast() {
return mOrderedHint;
}
/**
* Returns true if the receiver is currently processing the initial
* value of a sticky broadcast -- that is, the value that was last
* broadcast and is currently held in the sticky cache, so this is
* not directly the result of a broadcast right now.
*/
public final boolean isInitialStickyBroadcast() {
return mInitialStickyHint;
}
/**
* For internal use, sets the hint about whether this BroadcastReceiver is
* running in ordered mode.
*/
public final void setOrderedHint(boolean isOrdered) {
mOrderedHint = isOrdered;
}
/**
* For internal use, sets the hint about whether this BroadcastReceiver is
* receiving the initial sticky broadcast value. @hide
*/
public final void setInitialStickyHint(boolean isInitialSticky) {
mInitialStickyHint = isInitialSticky;
}
/**
* Control inclusion of debugging help for mismatched
* calls to {@ Context#registerReceiver(BroadcastReceiver, IntentFilter)
* Context.registerReceiver()}.
* If called with true, before given to registerReceiver(), then the
* callstack of the following {@link Context#unregisterReceiver(BroadcastReceiver)
* Context.unregisterReceiver()} call is retained, to be printed if a later
* incorrect unregister call is made. Note that doing this requires retaining
* information about the BroadcastReceiver for the lifetime of the app,
* resulting in a leak -- this should only be used for debugging.
*/
public final void setDebugUnregister(boolean debug) {
mDebugUnregister = debug;
}
/**
* Return the last value given to {@link #setDebugUnregister}.
*/
public final boolean getDebugUnregister() {
return mDebugUnregister;
}
void checkSynchronousHint() {
// Note that we don't assert when receiving the initial sticky value,
// since that may have come from an ordered broadcast. We'll catch
// them later when the real broadcast happens again.
if (mOrderedHint || mInitialStickyHint) {
return;
}
RuntimeException e = new RuntimeException(
"BroadcastReceiver trying to return result during a non-ordered broadcast");
e.fillInStackTrace();
Log.e("BroadcastReceiver", e.getMessage(), e);
}
private int mResultCode;
private String mResultData;
private Bundle mResultExtras;
private boolean mAbortBroadcast;
private boolean mDebugUnregister;
private boolean mOrderedHint;
private boolean mInitialStickyHint;
}
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