java.lang.Object | |
↳ | android.content.BroadcastReceiver |
Known Direct Subclasses |
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:
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.
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:
For information about how to use this class to receive and resolve intents, read the Intents and Intent Filters developer guide.
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 inadvertently conflict with other applications.
When you use 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 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 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
sendBroadcast(Intent, String)
or
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
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.
A BroadcastReceiver object is only valid for the duration of the call
to onReceive(Context, 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(Context, 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.
A process that is currently executing a BroadcastReceiver (that is,
currently running the code in its onReceive(Context, 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.
Nested Classes | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
BroadcastReceiver.PendingResult | State for a result that is pending for a broadcast receiver. |
Public Constructors | |||||||||||
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Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Sets the flag indicating that this receiver should abort the
current broadcast; only works with broadcasts sent through
Context.sendOrderedBroadcast . | |||||||||||
Clears the flag indicating that this receiver should abort the current
broadcast.
| |||||||||||
Returns the flag indicating whether or not this receiver should
abort the current broadcast.
| |||||||||||
Return the last value given to
setDebugUnregister(boolean) . | |||||||||||
Retrieve the current result code, as set by the previous receiver.
| |||||||||||
Retrieve the current result data, as set by the previous receiver.
| |||||||||||
Retrieve the current result extra data, as set by the previous receiver.
| |||||||||||
This can be called by an application in
onReceive(Context, Intent) to allow
it to keep the broadcast active after returning from that function. | |||||||||||
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.
| |||||||||||
Returns true if the receiver is currently processing an ordered
broadcast.
| |||||||||||
This method is called when the BroadcastReceiver is receiving an Intent
broadcast.
| |||||||||||
Provide a binder to an already-running service.
| |||||||||||
Control inclusion of debugging help for mismatched
calls to
Context.registerReceiver() . | |||||||||||
For internal use, sets the hint about whether this BroadcastReceiver is
running in ordered mode.
| |||||||||||
Change all of the result data returned from this broadcasts; only works
with broadcasts sent through
Context.sendOrderedBroadcast . | |||||||||||
Change the current result code of this broadcast; only works with
broadcasts sent through
Context.sendOrderedBroadcast . | |||||||||||
Change the current result data of this broadcast; only works with
broadcasts sent through
Context.sendOrderedBroadcast . | |||||||||||
Change the current result extras of this broadcast; only works with
broadcasts sent through
Context.sendOrderedBroadcast . |
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
|
Sets the flag indicating that this receiver should abort the
current broadcast; only works with broadcasts sent through
Context.sendOrderedBroadcast
. This will prevent
any other broadcast receivers from receiving the broadcast. It will still
call onReceive(Context, Intent)
of the BroadcastReceiver that the caller of
Context.sendOrderedBroadcast
passed in.
This method does not work with non-ordered broadcasts such
as those sent with Context.sendBroadcast
Clears the flag indicating that this receiver should abort the current broadcast.
Returns the flag indicating whether or not this receiver should abort the current broadcast.
Return the last value given to setDebugUnregister(boolean)
.
Retrieve the current result code, as set by the previous receiver.
Retrieve the current result data, as set by the previous receiver. Often this is null.
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.
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. |
---|
This can be called by an application in onReceive(Context, Intent)
to allow
it to keep the broadcast active after returning from that function.
This does not change the expectation of being relatively
responsive to the broadcast (finishing it within 10s), but does allow
the implementation to move work related to it over to another thread
to avoid glitching the main UI thread due to disk IO.
BroadcastReceiver.PendingResult
representing the result of
the active broadcast. The BroadcastRecord itself is no longer active;
all data and other interaction must go through BroadcastReceiver.PendingResult
APIs. The PendingResult.finish()
method
must be called once processing of the broadcast is done.
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.
Returns true if the receiver is currently processing an ordered broadcast.
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
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
startService(Intent)
instead of
bindService(Intent, ServiceConnection, int)
. If you wish
to interact with a service that is already running, you can use
peekService(Context, Intent)
.
The Intent filters used in registerReceiver(BroadcastReceiver, 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.
context | The Context in which the receiver is running. |
---|---|
intent | The Intent being received. |
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 onReceive(Context, Intent)
.
myContext | The Context that had been passed to onReceive(Context, Intent) |
---|---|
service | The Intent indicating the service you wish to use. See startService(Intent) for more information.
|
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.
For internal use, sets the hint about whether this BroadcastReceiver is running in ordered mode.
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
code | The new result code. Often uses the
Activity RESULT_CANCELED and
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). |
Change the current result code of this broadcast; only works with
broadcasts sent through
Context.sendOrderedBroadcast
. Often uses the
Activity RESULT_CANCELED
and
RESULT_OK
constants, though the
actual meaning of this value is ultimately up to the broadcaster.
This method does not work with non-ordered broadcasts such
as those sent with Context.sendBroadcast
code | The new result code. |
---|
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
data | The new result data; may be null. |
---|
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
extras | The new extra data map; may be null. |
---|