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Android Reference

BroadcastReceiver


android.content

Class BroadcastReceiver

  • Direct Known Subclasses:
    AbortReceiver, AppWidgetProvider, DeviceAdminReceiver, DownloadManagerBaseTest.MultipleDownloadsCompletedReceiver, DownloadManagerBaseTest.WiFiChangedReceiver, LocalGrantedReceiver, LocalReceiver, RemoteGrantedReceiver, RemoteReceiver, ResultReceiver


    public abstract class BroadcastReceiver
    extends Object
    Base class for code that will receive intents sent by sendBroadcast().

    If you don't need to send broadcasts across applications, consider using this class with LocalBroadcastManager instead of the more general facilities described below. This will give you a much more efficient implementation (no cross-process communication needed) and allow you to avoid thinking about any security issues related to other applications being able to receive or send your broadcasts.

    You can either dynamically register an instance of this class with Context.registerReceiver() or statically publish an implementation through the <receiver> tag in your AndroidManifest.xml.

    Note: If registering a receiver in your Activity.onResume() implementation, you should unregister it in Activity.onPause(). (You won't receive intents when paused, and this will cut down on unnecessary system overhead). Do not unregister in Activity.onSaveInstanceState(), because this won't be called if the user moves back in the history stack.

    There are two major classes of broadcasts that can be received:

    • Normal broadcasts (sent with 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.
    • Ordered broadcasts (sent with 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 android:priority attribute of the matching intent-filter; receivers with the same priority will be run in an arbitrary order.

    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.

    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 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.

    The BroadcastReceiver class (when launched as a component through a manifest's <receiver> tag) is an important part of an application's overall lifecycle.

    Topics covered here:

    1. Security
    2. Receiver Lifecycle
    3. Process Lifecycle

    Developer Guides

    For information about how to use this class to receive and resolve intents, read the Intents and Intent Filters developer guide.

    Security

    Receivers used with the Context APIs are by their nature a cross-application facility, so you must consider how other applications may be able to abuse your use of them. Some things to consider are:

    • The Intent namespace is global. Make sure that Intent action names and other strings are written in a namespace you own, or else you may inadvertantly conflict with other applications.

    • When you use Context.registerReceiver(BroadcastReceiver, IntentFilter), any application may send broadcasts to that registered receiver. You can control who can send broadcasts to it through permissions described below.

    • When you publish a receiver in your application's manifest and specify intent-filters for it, any other application can send broadcasts to it regardless of the filters you specify. To prevent others from sending to it, make it unavailable to them with android:exported="false".

    • When you use Context.sendBroadcast(Intent) or related methods, normally any other application can receive these broadcasts. You can control who can receive such broadcasts through permissions described below. Alternatively, starting with Build.VERSION_CODES.ICE_CREAM_SANDWICH, you can also safely restrict the broadcast to a single application with Intent.setPackage

    None of these issues exist when using LocalBroadcastManager, since intents broadcast it never go outside of the current process.

    Access permissions can be enforced by either the sender or receiver of a broadcast.

    To enforce a permission when sending, you supply a non-null permission argument to Context.sendBroadcast(Intent, String) or Context.sendOrderedBroadcast(Intent, String, BroadcastReceiver, android.os.Handler, int, String, Bundle). Only receivers who have been granted this permission (by requesting it with the <uses-permission> tag in their AndroidManifest.xml) will be able to receive the broadcast.

    To enforce a permission when receiving, you supply a non-null permission when registering your receiver -- either when calling Context.registerReceiver(BroadcastReceiver, IntentFilter, String, android.os.Handler) or in the static <receiver> tag in your AndroidManifest.xml. Only broadcasters who have been granted this permission (by requesting it with the <uses-permission> tag in their AndroidManifest.xml) will be able to send an Intent to the receiver.

    See the Security and Permissions document for more information on permissions and security in general.

    Receiver Lifecycle

    A BroadcastReceiver object is only valid for the duration of the call to onReceive(android.content.Context, android.content.Intent). Once your code returns from this function, the system considers the object to be finished and no longer active.

    This has important repercussions to what you can do in an onReceive(android.content.Context, android.content.Intent) 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.

    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 NotificationManager API. For the latter, you can use Context.startService() to send a command to the service.

    Process Lifecycle

    A process that is currently executing a BroadcastReceiver (that is, currently running the code in its onReceive(android.content.Context, android.content.Intent) method) is considered to be a foreground process and will be kept running by the system except under cases of extreme memory pressure.

    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.

    This means that for longer-running operations you will often use a Service in conjunction with a BroadcastReceiver to keep the containing process active for the entire time of your operation.

    • Constructor Detail

      • BroadcastReceiver

        public BroadcastReceiver()
    • Method Detail

      • onReceive

        public abstract void onReceive(Context context,
                     Intent intent)
        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. This method is always called within the main thread of its process, unless you explicitly asked for it to be scheduled on a different thread using Context.registerReceiver(BroadcastReceiver, IntentFilter, String, android.os.Handler). When it runs on the main thread 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().

        If this BroadcastReceiver was launched through a <receiver> tag, then the object is no longer alive after returning from this function. This means you should not perform any operations that return a result to you asynchronously -- in particular, for interacting with services, you should use Context.startService(Intent) instead of Context.bindService(Intent, ServiceConnection, int). If you wish to interact with a service that is already running, you can use peekService(android.content.Context, android.content.Intent).

        The Intent filters used in Context.registerReceiver(android.content.BroadcastReceiver, android.content.IntentFilter) and in application manifests are 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, onReceive() implementations should respond only to known actions, ignoring any unexpected Intents that they may receive.

        Parameters:
        context - The Context in which the receiver is running.
        intent - The Intent being received.
      • getResultCode

        public final int getResultCode()
        Retrieve the current result code, as set by the previous receiver.
        Returns:
        int The current result code.
      • setResultData

        public final void setResultData(String data)
        Change the current result data of this broadcast; only works with broadcasts sent through Context.sendOrderedBroadcast. This is an arbitrary string whose interpretation is up to the broadcaster.

        This method does not work with non-ordered broadcasts such as those sent with Context.sendBroadcast

        Parameters:
        data - The new result data; may be null.
        See Also:
        setResult(int, String, Bundle)
      • getResultData

        public final String getResultData()
        Retrieve the current result data, as set by the previous receiver. Often this is null.
        Returns:
        String The current result data; may be null.
      • setResultExtras

        public final void setResultExtras(Bundle extras)
        Change the current result extras of this broadcast; only works with broadcasts sent through 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).

        This method does not work with non-ordered broadcasts such as those sent with Context.sendBroadcast

        Parameters:
        extras - The new extra data map; may be null.
        See Also:
        setResult(int, String, Bundle)
      • getResultExtras

        public final Bundle getResultExtras(boolean makeMap)
        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.
        Parameters:
        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.
        Returns:
        Map The current extras map.
      • setResult

        public final void setResult(int code,
                     String data,
                     Bundle extras)
        Change all of the result data returned from this broadcasts; only works with broadcasts sent through Context.sendOrderedBroadcast. All current result data is replaced by the value given to this method.

        This method does not work with non-ordered broadcasts such as those sent with Context.sendBroadcast

        Parameters:
        code - The new result code. Often uses the Activity Activity.RESULT_CANCELED and Activity.RESULT_OK constants, though the actual meaning of this value is ultimately up to the broadcaster.
        data - The new result data. This is an arbitrary string whose interpretation is up to the broadcaster; may be null.
        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).
      • getAbortBroadcast

        public final boolean getAbortBroadcast()
        Returns the flag indicating whether or not this receiver should abort the current broadcast.
        Returns:
        True if the broadcast should be aborted.
      • clearAbortBroadcast

        public final void clearAbortBroadcast()
        Clears the flag indicating that this receiver should abort the current broadcast.
      • isOrderedBroadcast

        public final boolean isOrderedBroadcast()
        Returns true if the receiver is currently processing an ordered broadcast.
      • isInitialStickyBroadcast

        public final boolean isInitialStickyBroadcast()
        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.
      • setOrderedHint

        public final void setOrderedHint(boolean isOrdered)
        For internal use, sets the hint about whether this BroadcastReceiver is running in ordered mode.
      • setPendingResult

        public final void setPendingResult(BroadcastReceiver.PendingResult result)
        For internal use to set the result data that is active. @hide
      • getSendingUserId

        public int getSendingUserId()
      • setDebugUnregister

        public final void setDebugUnregister(boolean debug)
        Control inclusion of debugging help for mismatched calls to Context.registerReceiver(). If called with true, before given to registerReceiver(), then the callstack of the following 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.


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