public
abstract
class
Service
extends ContextWrapper
implements
ComponentCallbacks2
| java.lang.Object | |||
| ↳ | android.content.Context | ||
| ↳ | android.content.ContextWrapper | ||
| ↳ | android.app.Service | ||
 Known Direct Subclasses
|
|
Known Indirect Subclasses
|
A Service is an application component representing either an application's desire
to perform a longer-running operation while not interacting with the user
or to supply functionality for other applications to use. Each service
class must have a corresponding
<service>
declaration in its package's AndroidManifest.xml. Services
can be started with
Context.startService() and
Context.bindService().
Note that services, like other application objects, run in the main
thread of their hosting process. This means that, if your service is going
to do any CPU intensive (such as MP3 playback) or blocking (such as
networking) operations, it should spawn its own thread in which to do that
work. More information on this can be found in
Processes and
Threads. The IntentService class is available
as a standard implementation of Service that has its own thread where it
schedules its work to be done.
Topics covered here:
For a detailed discussion about how to create services, read the Services developer guide.
Most confusion about the Service class actually revolves around what it is not:
Thus a Service itself is actually very simple, providing two main features:
Developers
Context.startService(), which
ask the system to schedule work for the service, to be run until the service
or someone else explicitly stop it.
Context.bindService(), which
allows a long-standing connection to be made to the service in order to
interact with it.
When a Service component is actually created, for either of these reasons,
all that the system actually does is instantiate the component
and call its onCreate() and any other appropriate callbacks on the
main thread. It is up to the Service to implement these with the appropriate
behavior, such as creating a secondary thread in which it does its work.
Note that because Service itself is so simple, you can make your interaction with it as simple or complicated as you want: from treating it as a local Java object that you make direct method calls on (as illustrated by Local Service Sample), to providing a full remoteable interface using AIDL.
There are two reasons that a service can be run by the system. If someone
calls Context.startService() then the system will
retrieve the service (creating it and calling its onCreate() method
if needed) and then call its onStartCommand(Intent, int, int) method with the
arguments supplied by the client. The service will at this point continue
running until Context.stopService() or
stopSelf() is called. Note that multiple calls to
Context.startService() do not nest (though they do result in multiple corresponding
calls to onStartCommand()), so no matter how many times it is started a service
will be stopped once Context.stopService() or stopSelf() is called; however,
services can use their stopSelf(int) method to ensure the service is
not stopped until started intents have been processed.
For started services, there are two additional major modes of operation
they can decide to run in, depending on the value they return from
onStartCommand(): START_STICKY is used for services that are
explicitly started and stopped as needed, while START_NOT_STICKY
or START_REDELIVER_INTENT are used for services that should only
remain running while processing any commands sent to them. See the linked
documentation for more detail on the semantics.
Clients can also use Context.bindService() to
obtain a persistent connection to a service. This likewise creates the
service if it is not already running (calling onCreate() while
doing so), but does not call onStartCommand(). The client will receive the
IBinder object that the service returns from its
onBind(Intent) method, allowing the client to then make calls back
to the service. The service will remain running as long as the connection
is established (whether or not the client retains a reference on the
service's IBinder). Usually the IBinder returned is for a complex
interface that has been written
in aidl.
A service can be both started and have connections bound to it. In such
a case, the system will keep the service running as long as either it is
started or there are one or more connections to it with the
Context.BIND_AUTO_CREATE
flag. Once neither
of these situations hold, the service's onDestroy() method is called
and the service is effectively terminated. All cleanup (stopping threads,
unregistering receivers) should be complete upon returning from onDestroy().
Global access to a service can be enforced when it is declared in its
manifest's <service>
tag. By doing so, other applications will need to declare a corresponding
<uses-permission>
element in their own manifest to be able to start, stop, or bind to
the service.
As of GINGERBREAD, when using
Context.startService(Intent), you can
also set Intent.FLAG_GRANT_READ_URI_PERMISSION and/or Intent.FLAG_GRANT_WRITE_URI_PERMISSION on the Intent. This will grant the
Service temporary access to the specific URIs in the Intent. Access will
remain until the Service has called stopSelf(int) for that start
command or a later one, or until the Service has been completely stopped.
This works for granting access to the other apps that have not requested
the permission protecting the Service, or even when the Service is not
exported at all.
In addition, a service can protect individual IPC calls into it with
permissions, by calling the
checkCallingPermission(String)
method before executing the implementation of that call.
See the Security and Permissions document for more information on permissions and security in general.
The Android system will attempt to keep the process hosting a service around as long as the service has been started or has clients bound to it. When running low on memory and needing to kill existing processes, the priority of a process hosting the service will be the higher of the following possibilities:
If the service is currently executing code in its
onCreate(), onStartCommand(),
or onDestroy() methods, then the hosting process will
be a foreground process to ensure this code can execute without
being killed.
If the service has been started, then its hosting process is considered to be less important than any processes that are currently visible to the user on-screen, but more important than any process not visible. Because only a few processes are generally visible to the user, this means that the service should not be killed except in low memory conditions. However, since the user is not directly aware of a background service, in that state it is considered a valid candidate to kill, and you should be prepared for this to happen. In particular, long-running services will be increasingly likely to kill and are guaranteed to be killed (and restarted if appropriate) if they remain started long enough.
If there are clients bound to the service, then the service's hosting
process is never less important than the most important client. That is,
if one of its clients is visible to the user, then the service itself is
considered to be visible. The way a client's importance impacts the service's
importance can be adjusted through BIND_ABOVE_CLIENT,
BIND_ALLOW_OOM_MANAGEMENT, BIND_WAIVE_PRIORITY,
BIND_IMPORTANT, and BIND_ADJUST_WITH_ACTIVITY.
A started service can use the startForeground(int, Notification)
API to put the service in a foreground state, where the system considers
it to be something the user is actively aware of and thus not a candidate
for killing when low on memory. (It is still theoretically possible for
the service to be killed under extreme memory pressure from the current
foreground application, but in practice this should not be a concern.)
Note this means that most of the time your service is running, it may
be killed by the system if it is under heavy memory pressure. If this
happens, the system will later try to restart the service. An important
consequence of this is that if you implement onStartCommand()
to schedule work to be done asynchronously or in another thread, then you
may want to use START_FLAG_REDELIVERY to have the system
re-deliver an Intent for you so that it does not get lost if your service
is killed while processing it.
Other application components running in the same process as the service
(such as an Activity) can, of course, increase the
importance of the overall
process beyond just the importance of the service itself.
One of the most common uses of a Service is as a secondary component running alongside other parts of an application, in the same process as the rest of the components. All components of an .apk run in the same process unless explicitly stated otherwise, so this is a typical situation.
When used in this way, by assuming the components are in the same process, you can greatly simplify the interaction between them: clients of the service can simply cast the IBinder they receive from it to a concrete class published by the service.
An example of this use of a Service is shown here. First is the Service itself, publishing a custom class when bound:
public class LocalService extends Service {
private NotificationManager mNM;
// Unique Identification Number for the Notification.
// We use it on Notification start, and to cancel it.
private int NOTIFICATION = R.string.local_service_started;
/**
* Class for clients to access. Because we know this service always
* runs in the same process as its clients, we don't need to deal with
* IPC.
*/
public class LocalBinder extends Binder {
LocalService getService() {
return LocalService.this;
}
}
@Override
public void onCreate() {
mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
// Display a notification about us starting. We put an icon in the status bar.
showNotification();
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.i("LocalService", "Received start id " + startId + ": " + intent);
return START_NOT_STICKY;
}
@Override
public void onDestroy() {
// Cancel the persistent notification.
mNM.cancel(NOTIFICATION);
// Tell the user we stopped.
Toast.makeText(this, R.string.local_service_stopped, Toast.LENGTH_SHORT).show();
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
// This is the object that receives interactions from clients. See
// RemoteService for a more complete example.
private final IBinder mBinder = new LocalBinder();
/**
* Show a notification while this service is running.
*/
private void showNotification() {
// In this sample, we'll use the same text for the ticker and the expanded notification
CharSequence text = getText(R.string.local_service_started);
// The PendingIntent to launch our activity if the user selects this notification
PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
new Intent(this, LocalServiceActivities.Controller.class), 0);
// Set the info for the views that show in the notification panel.
Notification notification = new Notification.Builder(this)
.setSmallIcon(R.drawable.stat_sample) // the status icon
.setTicker(text) // the status text
.setWhen(System.currentTimeMillis()) // the time stamp
.setContentTitle(getText(R.string.local_service_label)) // the label of the entry
.setContentText(text) // the contents of the entry
.setContentIntent(contentIntent) // The intent to send when the entry is clicked
.build();
// Send the notification.
mNM.notify(NOTIFICATION, notification);
}
}
With that done, one can now write client code that directly accesses the running service, such as:
private LocalService mBoundService;
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
// This is called when the connection with the service has been
// established, giving us the service object we can use to
// interact with the service. Because we have bound to a explicit
// service that we know is running in our own process, we can
// cast its IBinder to a concrete class and directly access it.
mBoundService = ((LocalService.LocalBinder)service).getService();
// Tell the user about this for our demo.
Toast.makeText(Binding.this, R.string.local_service_connected,
Toast.LENGTH_SHORT).show();
}
public void onServiceDisconnected(ComponentName className) {
// This is called when the connection with the service has been
// unexpectedly disconnected -- that is, its process crashed.
// Because it is running in our same process, we should never
// see this happen.
mBoundService = null;
Toast.makeText(Binding.this, R.string.local_service_disconnected,
Toast.LENGTH_SHORT).show();
}
};
void doBindService() {
// Establish a connection with the service. We use an explicit
// class name because we want a specific service implementation that
// we know will be running in our own process (and thus won't be
// supporting component replacement by other applications).
bindService(new Intent(Binding.this,
LocalService.class), mConnection, Context.BIND_AUTO_CREATE);
mIsBound = true;
}
void doUnbindService() {
if (mIsBound) {
// Detach our existing connection.
unbindService(mConnection);
mIsBound = false;
}
}
@Override
protected void onDestroy() {
super.onDestroy();
doUnbindService();
}
If you need to be able to write a Service that can perform complicated
communication with clients in remote processes (beyond simply the use of
Context.startService to send
commands to it), then you can use the Messenger class
instead of writing full AIDL files.
An example of a Service that uses Messenger as its client interface is shown here. First is the Service itself, publishing a Messenger to an internal Handler when bound:
public class MessengerService extends Service {
/** For showing and hiding our notification. */
NotificationManager mNM;
/** Keeps track of all current registered clients. */
ArrayList<Messenger> mClients = new ArrayList<Messenger>();
/** Holds last value set by a client. */
int mValue = 0;
/**
* Command to the service to register a client, receiving callbacks
* from the service. The Message's replyTo field must be a Messenger of
* the client where callbacks should be sent.
*/
static final int MSG_REGISTER_CLIENT = 1;
/**
* Command to the service to unregister a client, ot stop receiving callbacks
* from the service. The Message's replyTo field must be a Messenger of
* the client as previously given with MSG_REGISTER_CLIENT.
*/
static final int MSG_UNREGISTER_CLIENT = 2;
/**
* Command to service to set a new value. This can be sent to the
* service to supply a new value, and will be sent by the service to
* any registered clients with the new value.
*/
static final int MSG_SET_VALUE = 3;
/**
* Handler of incoming messages from clients.
*/
class IncomingHandler extends Handler {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_REGISTER_CLIENT:
mClients.add(msg.replyTo);
break;
case MSG_UNREGISTER_CLIENT:
mClients.remove(msg.replyTo);
break;
case MSG_SET_VALUE:
mValue = msg.arg1;
for (int i=mClients.size()-1; i>=0; i--) {
try {
mClients.get(i).send(Message.obtain(null,
MSG_SET_VALUE, mValue, 0));
} catch (RemoteException e) {
// The client is dead. Remove it from the list;
// we are going through the list from back to front
// so this is safe to do inside the loop.
mClients.remove(i);
}
}
break;
default:
super.handleMessage(msg);
}
}
}
/**
* Target we publish for clients to send messages to IncomingHandler.
*/
final Messenger mMessenger = new Messenger(new IncomingHandler());
@Override
public void onCreate() {
mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
// Display a notification about us starting.
showNotification();
}
@Override
public void onDestroy() {
// Cancel the persistent notification.
mNM.cancel(R.string.remote_service_started);
// Tell the user we stopped.
Toast.makeText(this, R.string.remote_service_stopped, Toast.LENGTH_SHORT).show();
}
/**
* When binding to the service, we return an interface to our messenger
* for sending messages to the service.
*/
@Override
public IBinder onBind(Intent intent) {
return mMessenger.getBinder();
}
/**
* Show a notification while this service is running.
*/
private void showNotification() {
// In this sample, we'll use the same text for the ticker and the expanded notification
CharSequence text = getText(R.string.remote_service_started);
// The PendingIntent to launch our activity if the user selects this notification
PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
new Intent(this, Controller.class), 0);
// Set the info for the views that show in the notification panel.
Notification notification = new Notification.Builder(this)
.setSmallIcon(R.drawable.stat_sample) // the status icon
.setTicker(text) // the status text
.setWhen(System.currentTimeMillis()) // the time stamp
.setContentTitle(getText(R.string.local_service_label)) // the label of the entry
.setContentText(text) // the contents of the entry
.setContentIntent(contentIntent) // The intent to send when the entry is clicked
.build();
// Send the notification.
// We use a string id because it is a unique number. We use it later to cancel.
mNM.notify(R.string.remote_service_started, notification);
}
}
If we want to make this service run in a remote process (instead of the
standard one for its .apk), we can use android:process in its
manifest tag to specify one:
<service android:name=".app.MessengerService"
android:process=":remote" />
Note that the name "remote" chosen here is arbitrary, and you can use other names if you want additional processes. The ':' prefix appends the name to your package's standard process name.
With that done, clients can now bind to the service and send messages to it. Note that this allows clients to register with it to receive messages back as well:
/** Messenger for communicating with service. */
Messenger mService = null;
/** Flag indicating whether we have called bind on the service. */
boolean mIsBound;
/** Some text view we are using to show state information. */
TextView mCallbackText;
/**
* Handler of incoming messages from service.
*/
class IncomingHandler extends Handler {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MessengerService.MSG_SET_VALUE:
mCallbackText.setText("Received from service: " + msg.arg1);
break;
default:
super.handleMessage(msg);
}
}
}
/**
* Target we publish for clients to send messages to IncomingHandler.
*/
final Messenger mMessenger = new Messenger(new IncomingHandler());
/**
* Class for interacting with the main interface of the service.
*/
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className,
IBinder service) {
// This is called when the connection with the service has been
// established, giving us the service object we can use to
// interact with the service. We are communicating with our
// service through an IDL interface, so get a client-side
// representation of that from the raw service object.
mService = new Messenger(service);
mCallbackText.setText("Attached.");
// We want to monitor the service for as long as we are
// connected to it.
try {
Message msg = Message.obtain(null,
MessengerService.MSG_REGISTER_CLIENT);
msg.replyTo = mMessenger;
mService.send(msg);
// Give it some value as an example.
msg = Message.obtain(null,
MessengerService.MSG_SET_VALUE, this.hashCode(), 0);
mService.send(msg);
} catch (RemoteException e) {
// In this case the service has crashed before we could even
// do anything with it; we can count on soon being
// disconnected (and then reconnected if it can be restarted)
// so there is no need to do anything here.
}
// As part of the sample, tell the user what happened.
Toast.makeText(Binding.this, R.string.remote_service_connected,
Toast.LENGTH_SHORT).show();
}
public void onServiceDisconnected(ComponentName className) {
// This is called when the connection with the service has been
// unexpectedly disconnected -- that is, its process crashed.
mService = null;
mCallbackText.setText("Disconnected.");
// As part of the sample, tell the user what happened.
Toast.makeText(Binding.this, R.string.remote_service_disconnected,
Toast.LENGTH_SHORT).show();
}
};
void doBindService() {
// Establish a connection with the service. We use an explicit
// class name because there is no reason to be able to let other
// applications replace our component.
bindService(new Intent(Binding.this,
MessengerService.class), mConnection, Context.BIND_AUTO_CREATE);
mIsBound = true;
mCallbackText.setText("Binding.");
}
void doUnbindService() {
if (mIsBound) {
// If we have received the service, and hence registered with
// it, then now is the time to unregister.
if (mService != null) {
try {
Message msg = Message.obtain(null,
MessengerService.MSG_UNREGISTER_CLIENT);
msg.replyTo = mMessenger;
mService.send(msg);
} catch (RemoteException e) {
// There is nothing special we need to do if the service
// has crashed.
}
}
// Detach our existing connection.
unbindService(mConnection);
mIsBound = false;
mCallbackText.setText("Unbinding.");
}
}
Constants | |
|---|---|
int |
START_CONTINUATION_MASK
Bits returned by |
int |
START_FLAG_REDELIVERY
This flag is set in |
int |
START_FLAG_RETRY
This flag is set in |
int |
START_NOT_STICKY
Constant to return from |
int |
START_REDELIVER_INTENT
Constant to return from |
int |
START_STICKY
Constant to return from |
int |
START_STICKY_COMPATIBILITY
Constant to return from |
int |
STOP_FOREGROUND_DETACH
Flag for |
int |
STOP_FOREGROUND_REMOVE
Flag for |
Inherited constants |
|---|
From
class
android.content.Context
|
From
interface
android.content.ComponentCallbacks2
|
Public constructors | |
|---|---|
Service()
|
|
Public methods | |
|---|---|
final
Application
|
getApplication()
Return the application that owns this service. |
abstract
IBinder
|
onBind(Intent intent)
Return the communication channel to the service. |
void
|
onConfigurationChanged(Configuration newConfig)
Called by the system when the device configuration changes while your component is running. |
void
|
onCreate()
Called by the system when the service is first created. |
void
|
onDestroy()
Called by the system to notify a Service that it is no longer used and is being removed. |
void
|
onLowMemory()
This is called when the overall system is running low on memory, and actively running processes should trim their memory usage. |
void
|
onRebind(Intent intent)
Called when new clients have connected to the service, after it had
previously been notified that all had disconnected in its
|
void
|
onStart(Intent intent, int startId)
This method was deprecated
in API level 5.
Implement |
int
|
onStartCommand(Intent intent, int flags, int startId)
Called by the system every time a client explicitly starts the service by calling
|
void
|
onTaskRemoved(Intent rootIntent)
This is called if the service is currently running and the user has removed a task that comes from the service's application. |
void
|
onTrimMemory(int level)
Called when the operating system has determined that it is a good time for a process to trim unneeded memory from its process. |
boolean
|
onUnbind(Intent intent)
Called when all clients have disconnected from a particular interface published by the service. |
final
void
|
startForeground(int id, Notification notification)
Make this service run in the foreground, supplying the ongoing notification to be shown to the user while in this state. |
final
void
|
stopForeground(int flags)
Remove this service from foreground state, allowing it to be killed if more memory is needed. |
final
void
|
stopForeground(boolean removeNotification)
Synonym for |
final
void
|
stopSelf()
Stop the service, if it was previously started. |
final
void
|
stopSelf(int startId)
Old version of |
final
boolean
|
stopSelfResult(int startId)
Stop the service if the most recent time it was started was startId. |
Protected methods | |
|---|---|
void
|
dump(FileDescriptor fd, PrintWriter writer, String[] args)
Print the Service's state into the given stream. |
Inherited methods | |
|---|---|
From
class
android.content.ContextWrapper
| |
From
class
android.content.Context
| |
From
class
java.lang.Object
| |
From
interface
android.content.ComponentCallbacks2
| |
From
interface
android.content.ComponentCallbacks
| |
int START_CONTINUATION_MASK
Bits returned by onStartCommand(Intent, int, int) describing how to continue
the service if it is killed. May be START_STICKY,
START_NOT_STICKY, START_REDELIVER_INTENT,
or START_STICKY_COMPATIBILITY.
Constant Value: 15 (0x0000000f)
int START_FLAG_REDELIVERY
This flag is set in onStartCommand(Intent, int, int) if the Intent is a
re-delivery of a previously delivered intent, because the service
had previously returned START_REDELIVER_INTENT but had been
killed before calling stopSelf(int) for that Intent.
Constant Value: 1 (0x00000001)
int START_FLAG_RETRY
This flag is set in onStartCommand(Intent, int, int) if the Intent is a
retry because the original attempt never got to or returned from
onStartCommand(Intent, int, int).
Constant Value: 2 (0x00000002)
int START_NOT_STICKY
Constant to return from onStartCommand(Intent, int, int): if this service's
process is killed while it is started (after returning from
onStartCommand(Intent, int, int)), and there are no new start intents to
deliver to it, then take the service out of the started state and
don't recreate until a future explicit call to
Context.startService(Intent). The
service will not receive a onStartCommand(Intent, int, int)
call with a null Intent because it will not be re-started if there
are no pending Intents to deliver.
This mode makes sense for things that want to do some work as a
result of being started, but can be stopped when under memory pressure
and will explicit start themselves again later to do more work. An
example of such a service would be one that polls for data from
a server: it could schedule an alarm to poll every N minutes by having
the alarm start its service. When its onStartCommand(Intent, int, int) is
called from the alarm, it schedules a new alarm for N minutes later,
and spawns a thread to do its networking. If its process is killed
while doing that check, the service will not be restarted until the
alarm goes off.
Constant Value: 2 (0x00000002)
int START_REDELIVER_INTENT
Constant to return from onStartCommand(Intent, int, int): if this service's
process is killed while it is started (after returning from
onStartCommand(Intent, int, int)), then it will be scheduled for a restart
and the last delivered Intent re-delivered to it again via
onStartCommand(Intent, int, int). This Intent will remain scheduled for
redelivery until the service calls stopSelf(int) with the
start ID provided to onStartCommand(Intent, int, int). The
service will not receive a onStartCommand(Intent, int, int)
call with a null Intent because it will will only be re-started if
it is not finished processing all Intents sent to it (and any such
pending events will be delivered at the point of restart).
Constant Value: 3 (0x00000003)
int START_STICKY
Constant to return from onStartCommand(Intent, int, int): if this service's
process is killed while it is started (after returning from
onStartCommand(Intent, int, int)), then leave it in the started state but
don't retain this delivered intent. Later the system will try to
re-create the service. Because it is in the started state, it will
guarantee to call onStartCommand(Intent, int, int) after creating the new
service instance; if there are not any pending start commands to be
delivered to the service, it will be called with a null intent
object, so you must take care to check for this.
This mode makes sense for things that will be explicitly started and stopped to run for arbitrary periods of time, such as a service performing background music playback.
Constant Value: 1 (0x00000001)
int START_STICKY_COMPATIBILITY
Constant to return from onStartCommand(Intent, int, int): compatibility
version of START_STICKY that does not guarantee that
onStartCommand(Intent, int, int) will be called again after being killed.
Constant Value: 0 (0x00000000)
int STOP_FOREGROUND_DETACH
Flag for stopForeground(int): if set, the notification previously provided
to startForeground(int, Notification) will be detached from the service. Only makes sense
when STOP_FOREGROUND_REMOVE is not set -- in this case, the notification
will remain shown, but be completely detached from the service and so no longer changed
except through direct calls to the notification manager.
Constant Value: 2 (0x00000002)
int STOP_FOREGROUND_REMOVE
Flag for stopForeground(int): if set, the notification previously provided
to startForeground(int, Notification) will be removed. Otherwise it will remain
until a later call (to startForeground(int, Notification) or
stopForeground(int) removes it, or the service is destroyed.
Constant Value: 1 (0x00000001)
Application getApplication ()
Return the application that owns this service.
| Returns | |
|---|---|
Application |
|
IBinder onBind (Intent intent)
Return the communication channel to the service. May return null if
clients can not bind to the service. The returned
IBinder is usually for a complex interface
that has been described using
aidl.
Note that unlike other application components, calls on to the IBinder interface returned here may not happen on the main thread of the process. More information about the main thread can be found in Processes and Threads.
| Parameters | |
|---|---|
intent |
Intent:
The Intent that was used to bind to this service,
as given to Context.bindService. Note that any extras that were included with
the Intent at that point will not be seen here. |
| Returns | |
|---|---|
IBinder |
Return an IBinder through which clients can call on to the service. |
void onConfigurationChanged (Configuration newConfig)
Called by the system when the device configuration changes while your component is running. Note that, unlike activities, other components are never restarted when a configuration changes: they must always deal with the results of the change, such as by re-retrieving resources.
At the time that this function has been called, your Resources object will have been updated to return resource values matching the new configuration.
For more information, read Handling Runtime Changes.
| Parameters | |
|---|---|
newConfig |
Configuration:
The new device configuration.
|
void onCreate ()
Called by the system when the service is first created. Do not call this method directly.
void onDestroy ()
Called by the system to notify a Service that it is no longer used and is being removed. The service should clean up any resources it holds (threads, registered receivers, etc) at this point. Upon return, there will be no more calls in to this Service object and it is effectively dead. Do not call this method directly.
void onLowMemory ()
This is called when the overall system is running low on memory, and actively running processes should trim their memory usage. While the exact point at which this will be called is not defined, generally it will happen when all background process have been killed. That is, before reaching the point of killing processes hosting service and foreground UI that we would like to avoid killing.
You should implement this method to release any caches or other unnecessary resources you may be holding on to. The system will perform a garbage collection for you after returning from this method.
Preferably, you should implement onTrimMemory(int) from
ComponentCallbacks2 to incrementally unload your resources based on various
levels of memory demands. That API is available for API level 14 and higher, so you should
only use this onLowMemory() method as a fallback for older versions, which can be
treated the same as onTrimMemory(int) with the TRIM_MEMORY_COMPLETE level.
void onRebind (Intent intent)
Called when new clients have connected to the service, after it had
previously been notified that all had disconnected in its
onUnbind(Intent). This will only be called if the implementation
of onUnbind(Intent) was overridden to return true.
| Parameters | |
|---|---|
intent |
Intent:
The Intent that was used to bind to this service,
as given to Context.bindService. Note that any extras that were included with
the Intent at that point will not be seen here.
|
void onStart (Intent intent, int startId)
This method was deprecated
in API level 5.
Implement onStartCommand(Intent, int, int) instead.
| Parameters | |
|---|---|
intent |
Intent
|
startId |
int
|
int onStartCommand (Intent intent, int flags, int startId)
Called by the system every time a client explicitly starts the service by calling
startService(Intent), providing the arguments it supplied and a
unique integer token representing the start request. Do not call this method directly.
For backwards compatibility, the default implementation calls
onStart(Intent, int) and returns either START_STICKY
or START_STICKY_COMPATIBILITY.
If you need your application to run on platform versions prior to API
level 5, you can use the following model to handle the older onStart(Intent, int)
callback in that case. The handleCommand method is implemented by
you as appropriate:
// This is the old onStart method that will be called on the pre-2.0
// platform. On 2.0 or later we override onStartCommand() so this
// method will not be called.
@Override
public void onStart(Intent intent, int startId) {
handleCommand(intent);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
handleCommand(intent);
// We want this service to continue running until it is explicitly
// stopped, so return sticky.
return START_STICKY;
}
Note that the system calls this on your
service's main thread. A service's main thread is the same
thread where UI operations take place for Activities running in the
same process. You should always avoid stalling the main
thread's event loop. When doing long-running operations,
network calls, or heavy disk I/O, you should kick off a new
thread, or use AsyncTask.
| Parameters | |
|---|---|
intent |
Intent:
The Intent supplied to startService(Intent),
as given. This may be null if the service is being restarted after
its process has gone away, and it had previously returned anything
except START_STICKY_COMPATIBILITY. |
flags |
int:
Additional data about this start request. Currently either
0, START_FLAG_REDELIVERY, or START_FLAG_RETRY. |
startId |
int:
A unique integer representing this specific request to
start. Use with stopSelfResult(int). |
| Returns | |
|---|---|
int |
The return value indicates what semantics the system should
use for the service's current started state. It may be one of the
constants associated with the START_CONTINUATION_MASK bits. |
See also:
void onTaskRemoved (Intent rootIntent)
This is called if the service is currently running and the user has
removed a task that comes from the service's application. If you have
set ServiceInfo.FLAG_STOP_WITH_TASK
then you will not receive this callback; instead, the service will simply
be stopped.
| Parameters | |
|---|---|
rootIntent |
Intent:
The original root Intent that was used to launch
the task that is being removed.
|
void onTrimMemory (int level)
Called when the operating system has determined that it is a good time for a process to trim unneeded memory from its process. This will happen for example when it goes in the background and there is not enough memory to keep as many background processes running as desired. You should never compare to exact values of the level, since new intermediate values may be added -- you will typically want to compare if the value is greater or equal to a level you are interested in.
To retrieve the processes current trim level at any point, you can
use ActivityManager.getMyMemoryState(RunningAppProcessInfo).
| Parameters | |
|---|---|
level |
int:
The context of the trim, giving a hint of the amount of
trimming the application may like to perform. May be
TRIM_MEMORY_COMPLETE, TRIM_MEMORY_MODERATE,
TRIM_MEMORY_BACKGROUND, TRIM_MEMORY_UI_HIDDEN,
TRIM_MEMORY_RUNNING_CRITICAL, TRIM_MEMORY_RUNNING_LOW,
or TRIM_MEMORY_RUNNING_MODERATE.
|
boolean onUnbind (Intent intent)
Called when all clients have disconnected from a particular interface published by the service. The default implementation does nothing and returns false.
| Parameters | |
|---|---|
intent |
Intent:
The Intent that was used to bind to this service,
as given to Context.bindService. Note that any extras that were included with
the Intent at that point will not be seen here. |
| Returns | |
|---|---|
boolean |
Return true if you would like to have the service's
onRebind(Intent) method later called when new clients bind to it.
|
void startForeground (int id,
Notification notification)
Make this service run in the foreground, supplying the ongoing notification to be shown to the user while in this state. By default services are background, meaning that if the system needs to kill them to reclaim more memory (such as to display a large page in a web browser), they can be killed without too much harm. You can set this flag if killing your service would be disruptive to the user, such as if your service is performing background music playback, so the user would notice if their music stopped playing.
If you need your application to run on platform versions prior to API level 5, you can use the following model to call the the older setForeground() or this modern method as appropriate:
private static final Class<?>[] mSetForegroundSignature = new Class[] {
boolean.class};
private static final Class<?>[] mStartForegroundSignature = new Class[] {
int.class, Notification.class};
private static final Class<?>[] mStopForegroundSignature = new Class[] {
boolean.class};
private NotificationManager mNM;
private Method mSetForeground;
private Method mStartForeground;
private Method mStopForeground;
private Object[] mSetForegroundArgs = new Object[1];
private Object[] mStartForegroundArgs = new Object[2];
private Object[] mStopForegroundArgs = new Object[1];
void invokeMethod(Method method, Object[] args) {
try {
method.invoke(this, args);
} catch (InvocationTargetException e) {
// Should not happen.
Log.w("ApiDemos", "Unable to invoke method", e);
} catch (IllegalAccessException e) {
// Should not happen.
Log.w("ApiDemos", "Unable to invoke method", e);
}
}
/**
* This is a wrapper around the new startForeground method, using the older
* APIs if it is not available.
*/
void startForegroundCompat(int id, Notification notification) {
// If we have the new startForeground API, then use it.
if (mStartForeground != null) {
mStartForegroundArgs[0] = Integer.valueOf(id);
mStartForegroundArgs[1] = notification;
invokeMethod(mStartForeground, mStartForegroundArgs);
return;
}
// Fall back on the old API.
mSetForegroundArgs[0] = Boolean.TRUE;
invokeMethod(mSetForeground, mSetForegroundArgs);
mNM.notify(id, notification);
}
/**
* This is a wrapper around the new stopForeground method, using the older
* APIs if it is not available.
*/
void stopForegroundCompat(int id) {
// If we have the new stopForeground API, then use it.
if (mStopForeground != null) {
mStopForegroundArgs[0] = Boolean.TRUE;
invokeMethod(mStopForeground, mStopForegroundArgs);
return;
}
// Fall back on the old API. Note to cancel BEFORE changing the
// foreground state, since we could be killed at that point.
mNM.cancel(id);
mSetForegroundArgs[0] = Boolean.FALSE;
invokeMethod(mSetForeground, mSetForegroundArgs);
}
@Override
public void onCreate() {
mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
try {
mStartForeground = getClass().getMethod("startForeground",
mStartForegroundSignature);
mStopForeground = getClass().getMethod("stopForeground",
mStopForegroundSignature);
return;
} catch (NoSuchMethodException e) {
// Running on an older platform.
mStartForeground = mStopForeground = null;
}
try {
mSetForeground = getClass().getMethod("setForeground",
mSetForegroundSignature);
} catch (NoSuchMethodException e) {
throw new IllegalStateException(
"OS doesn't have Service.startForeground OR Service.setForeground!");
}
}
@Override
public void onDestroy() {
handleDestroy();
// Make sure our notification is gone.
stopForegroundCompat(R.string.foreground_service_started);
}
| Parameters | |
|---|---|
id |
int:
The identifier for this notification as per
NotificationManager.notify(int, Notification); must not be 0. |
notification |
Notification:
The Notification to be displayed. |
See also:
void stopForeground (int flags)
Remove this service from foreground state, allowing it to be killed if more memory is needed.
| Parameters | |
|---|---|
flags |
int:
Additional behavior options: STOP_FOREGROUND_REMOVE,
STOP_FOREGROUND_DETACH. |
See also:
void stopForeground (boolean removeNotification)
Synonym for stopForeground(int).
| Parameters | |
|---|---|
removeNotification |
boolean:
If true, the STOP_FOREGROUND_REMOVE flag
will be supplied. |
void stopSelf ()
Stop the service, if it was previously started. This is the same as
calling stopService(Intent) for this particular service.
See also:
void stopSelf (int startId)
Old version of stopSelfResult(int) that doesn't return a result.
| Parameters | |
|---|---|
startId |
int
|
See also:
boolean stopSelfResult (int startId)
Stop the service if the most recent time it was started was
startId. This is the same as calling stopService(Intent) for this particular service but allows you to
safely avoid stopping if there is a start request from a client that you
haven't yet seen in onStart(Intent, int).
Be careful about ordering of your calls to this function.. If you call this function with the most-recently received ID before you have called it for previously received IDs, the service will be immediately stopped anyway. If you may end up processing IDs out of order (such as by dispatching them on separate threads), then you are responsible for stopping them in the same order you received them.
| Parameters | |
|---|---|
startId |
int:
The most recent start identifier received in onStart(Intent, int). |
| Returns | |
|---|---|
boolean |
Returns true if the startId matches the last start request and the service will be stopped, else false. |
See also:
void dump (FileDescriptor fd, PrintWriter writer, String[] args)
Print the Service's state into the given stream. This gets invoked if
you run "adb shell dumpsys activity service <yourservicename>"
(note that for this command to work, the service must be running, and
you must specify a fully-qualified service name).
This is distinct from "dumpsys <servicename>", which only works for
named system services and which invokes the dump(FileDescriptor, String[]) method
on the IBinder interface registered with ServiceManager.
| Parameters | |
|---|---|
fd |
FileDescriptor:
The raw file descriptor that the dump is being sent to. |
writer |
PrintWriter:
The PrintWriter to which you should dump your state. This will be
closed for you after you return. |
args |
String:
additional arguments to the dump request.
|