The Service.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.app;
import android.content.ComponentCallbacks;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ContextWrapper;
import android.content.Context;
import android.content.res.Configuration;
import android.os.Build;
import android.os.RemoteException;
import android.os.IBinder;
import android.util.Log;
import java.io.FileDescriptor;
import java.io.PrintWriter;
/**
* 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
* {@link android.R.styleable#AndroidManifestService <service>}
* declaration in its package's <code>AndroidManifest.xml. Services
* can be started with
* {@link android.content.Context#startService Context.startService()} and
* {@link android.content.Context#bindService Context.bindService()}.
*
* <p>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
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>. The {@link IntentService} class is available
* as a standard implementation of Service that has its own thread where it
* schedules its work to be done.</p>
*
* <p>The Service class is an important part of an
* <a href="{@docRoot}guide/topics/fundamentals.html#lcycles">application's overall lifecycle.
*
* <p>Topics covered here:
* <ol>
* <li>What is a Service?
* <li>Service Lifecycle
* <li>Permissions
* <li>Process Lifecycle
* <li>Local Service Sample
* <li>Remote Messenger Service Sample
* </ol>
*
* <a name="WhatIsAService">
* <h3>What is a Service?
*
* <p>Most confusion about the Service class actually revolves around what
* it is <em>not:
*
* <ul>
* <li> A Service is not a separate process. The Service object itself
* does not imply it is running in its own process; unless otherwise specified,
* it runs in the same process as the application it is part of.
* <li> A Service is not a thread. It is not a means itself to do work off
* of the main thread (to avoid Application Not Responding errors).
* </ul>
*
* <p>Thus a Service itself is actually very simple, providing two main features:
*
* <ul>
* <li>A facility for the application to tell the system about
* something it wants to be doing in the background (even when the user is not
* directly interacting with the application). This corresponds to calls to
* {@link android.content.Context#startService Context.startService()}, which
* ask the system to schedule work for the service, to be run until the service
* or someone else explicitly stop it.
* <li>A facility for an application to expose some of its functionality to
* other applications. This corresponds to calls to
* {@link android.content.Context#bindService Context.bindService()}, which
* allows a long-standing connection to be made to the service in order to
* interact with it.
* </ul>
*
* <p>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 {@link #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.</p>
*
* <p>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 <a href="#LocalServiceSample">Local Service Sample), to providing
* a full remoteable interface using AIDL.</p>
*
* <a name="ServiceLifecycle">
* <h3>Service Lifecycle
*
* <p>There are two reasons that a service can be run by the system. If someone
* calls {@link android.content.Context#startService Context.startService()} then the system will
* retrieve the service (creating it and calling its {@link #onCreate} method
* if needed) and then call its {@link #onStartCommand} method with the
* arguments supplied by the client. The service will at this point continue
* running until {@link android.content.Context#stopService Context.stopService()} or
* {@link #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 {@link #stopSelf(int)} method to ensure the service is
* not stopped until started intents have been processed.
*
* <p>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(): {@link #START_STICKY} is used for services that are
* explicitly started and stopped as needed, while {@link #START_NOT_STICKY}
* or {@link #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.
*
* <p>Clients can also use {@link android.content.Context#bindService Context.bindService()} to
* obtain a persistent connection to a service. This likewise creates the
* service if it is not already running (calling {@link #onCreate} while
* doing so), but does not call onStartCommand(). The client will receive the
* {@link android.os.IBinder} object that the service returns from its
* {@link #onBind} 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 <a href="{@docRoot}guide/developing/tools/aidl.html">written
* in aidl</a>.
*
* <p>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 <em>or there are one or more connections to it with the
* {@link android.content.Context#BIND_AUTO_CREATE Context.BIND_AUTO_CREATE}
* flag. Once neither
* of these situations hold, the service's {@link #onDestroy} method is called
* and the service is effectively terminated. All cleanup (stopping threads,
* unregistering receivers) should be complete upon returning from onDestroy().
*
* <a name="Permissions">
* <h3>Permissions
*
* <p>Global access to a service can be enforced when it is declared in its
* manifest's {@link android.R.styleable#AndroidManifestService <service>}
* tag. By doing so, other applications will need to declare a corresponding
* {@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>}
* element in their own manifest to be able to start, stop, or bind to
* the service.
*
* <p>In addition, a service can protect individual IPC calls into it with
* permissions, by calling the
* {@link #checkCallingPermission}
* method before executing the implementation of that call.
*
* <p>See the Security and Permissions
* document for more information on permissions and security in general.
*
* <a name="ProcessLifecycle">
* <h3>Process Lifecycle
*
* <p>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:
*
* <ul>
* <li>If the service is currently executing code in its
* {@link #onCreate onCreate()}, {@link #onStartCommand onStartCommand()},
* or {@link #onDestroy onDestroy()} methods, then the hosting process will
* be a foreground process to ensure this code can execute without
* being killed.
* <li>
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 extreme low memory conditions.
* <li>
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.
* <li>
A started service can use the {@link #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.)
* </ul>
*
* <p>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 {@link #onStartCommand onStartCommand()}
* to schedule work to be done asynchronously or in another thread, then you
* may want to use {@link #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.
*
* <p>Other application components running in the same process as the service
* (such as an {@link android.app.Activity}) can, of course, increase the
* importance of the overall
* process beyond just the importance of the service itself.
*
* <a name="LocalServiceSample">
* <h3>Local Service Sample
*
* <p>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.
*
* <p>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.
*
* <p>An example of this use of a Service is shown here. First is the Service
* itself, publishing a custom class when bound:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/LocalService.java
* service}
*
* <p>With that done, one can now write client code that directly accesses the
* running service, such as:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/LocalServiceActivities.java
* bind}
*
* <a name="RemoteMessengerServiceSample">
* <h3>Remote Messenger Service Sample
*
* <p>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
* {@link Context#startService(Intent) Context.startService} to send
* commands to it), then you can use the {@link android.os.Messenger} class
* instead of writing full AIDL files.
*
* <p>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:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/MessengerService.java
* service}
*
* <p>If we want to make this service run in a remote process (instead of the
* standard one for its .apk), we can use <code>android:process in its
* manifest tag to specify one:
*
* {@sample development/samples/ApiDemos/AndroidManifest.xml remote_service_declaration}
*
* <p>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.
*
* <p>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:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/MessengerServiceActivities.java
* bind}
*/
public abstract class Service extends ContextWrapper implements ComponentCallbacks {
private static final String TAG = "Service";
public Service() {
super(null);
}
/** Return the application that owns this service. */
public final Application getApplication() {
return mApplication;
}
/**
* Called by the system when the service is first created. Do not call this method directly.
*/
public void onCreate() {
}
/**
* @deprecated Implement {@link #onStartCommand(Intent, int, int)} instead.
*/
@Deprecated
public void onStart(Intent intent, int startId) {
}
/**
* Bits returned by {@link #onStartCommand} describing how to continue
* the service if it is killed. May be {@link #START_STICKY},
* {@link #START_NOT_STICKY}, {@link #START_REDELIVER_INTENT},
* or {@link #START_STICKY_COMPATIBILITY}.
*/
public static final int START_CONTINUATION_MASK = 0xf;
/**
* Constant to return from {@link #onStartCommand}: compatibility
* version of {@link #START_STICKY} that does not guarantee that
* {@link #onStartCommand} will be called again after being killed.
*/
public static final int START_STICKY_COMPATIBILITY = 0;
/**
* Constant to return from {@link #onStartCommand}: if this service's
* process is killed while it is started (after returning from
* {@link #onStartCommand}), 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 {@link #onStartCommand} 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.
*
* <p>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.
*/
public static final int START_STICKY = 1;
/**
* Constant to return from {@link #onStartCommand}: if this service's
* process is killed while it is started (after returning from
* {@link #onStartCommand}), 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
* {@link Context#startService Context.startService(Intent)}. The
* service will not receive a {@link #onStartCommand(Intent, int, int)}
* call with a null Intent because it will not be re-started if there
* are no pending Intents to deliver.
*
* <p>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 {@link #onStartCommand} 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.
*/
public static final int START_NOT_STICKY = 2;
/**
* Constant to return from {@link #onStartCommand}: if this service's
* process is killed while it is started (after returning from
* {@link #onStartCommand}), then it will be scheduled for a restart
* and the last delivered Intent re-delivered to it again via
* {@link #onStartCommand}. This Intent will remain scheduled for
* redelivery until the service calls {@link #stopSelf(int)} with the
* start ID provided to {@link #onStartCommand}. The
* service will not receive a {@link #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).
*/
public static final int START_REDELIVER_INTENT = 3;
/**
* This flag is set in {@link #onStartCommand} if the Intent is a
* re-delivery of a previously delivered intent, because the service
* had previously returned {@link #START_REDELIVER_INTENT} but had been
* killed before calling {@link #stopSelf(int)} for that Intent.
*/
public static final int START_FLAG_REDELIVERY = 0x0001;
/**
* This flag is set in {@link #onStartCommand} if the Intent is a
* a retry because the original attempt never got to or returned from
* {@link #onStartCommand(Intent, int, int)}.
*/
public static final int START_FLAG_RETRY = 0x0002;
/**
* Called by the system every time a client explicitly starts the service by calling
* {@link android.content.Context#startService}, providing the arguments it supplied and a
* unique integer token representing the start request. Do not call this method directly.
*
* <p>For backwards compatibility, the default implementation calls
* {@link #onStart} and returns either {@link #START_STICKY}
* or {@link #START_STICKY_COMPATIBILITY}.
*
* <p>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 {@link #onStart}
* callback in that case. The <code>handleCommand method is implemented by
* you as appropriate:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/ForegroundService.java
* start_compatibility}
*
* @param intent The Intent supplied to {@link android.content.Context#startService},
* 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 {@link #START_STICKY_COMPATIBILITY}.
* @param flags Additional data about this start request. Currently either
* 0, {@link #START_FLAG_REDELIVERY}, or {@link #START_FLAG_RETRY}.
* @param startId A unique integer representing this specific request to
* start. Use with {@link #stopSelfResult(int)}.
*
* @return 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 {@link #START_CONTINUATION_MASK} bits.
*
* @see #stopSelfResult(int)
*/
public int onStartCommand(Intent intent, int flags, int startId) {
onStart(intent, startId);
return mStartCompatibility ? START_STICKY_COMPATIBILITY : START_STICKY;
}
/**
* Called by the system to notify a Service that it is no longer used and is being removed. The
* service should clean up an 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.
*/
public void onDestroy() {
}
public void onConfigurationChanged(Configuration newConfig) {
}
public void onLowMemory() {
}
/**
* Return the communication channel to the service. May return null if
* clients can not bind to the service. The returned
* {@link android.os.IBinder} is usually for a complex interface
* that has been <a href="{@docRoot}guide/developing/tools/aidl.html">described using
* aidl</a>.
*
* <p>Note that unlike other application components, calls on to the
* IBinder interface returned here may not happen on the main thread
* of the process</em>. More information about this can be found
* in <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
*
* @param intent The Intent that was used to bind to this service,
* as given to {@link android.content.Context#bindService
* Context.bindService}. Note that any extras that were included with
* the Intent at that point will <em>not be seen here.
*
* @return Return an IBinder through which clients can call on to the
* service.
*/
public abstract IBinder onBind(Intent intent);
/**
* Called when all clients have disconnected from a particular interface
* published by the service. The default implementation does nothing and
* returns false.
*
* @param intent The Intent that was used to bind to this service,
* as given to {@link android.content.Context#bindService
* Context.bindService}. Note that any extras that were included with
* the Intent at that point will <em>not be seen here.
*
* @return Return true if you would like to have the service's
* {@link #onRebind} method later called when new clients bind to it.
*/
public boolean onUnbind(Intent intent) {
return false;
}
/**
* Called when new clients have connected to the service, after it had
* previously been notified that all had disconnected in its
* {@link #onUnbind}. This will only be called if the implementation
* of {@link #onUnbind} was overridden to return true.
*
* @param intent The Intent that was used to bind to this service,
* as given to {@link android.content.Context#bindService
* Context.bindService}. Note that any extras that were included with
* the Intent at that point will <em>not be seen here.
*/
public void onRebind(Intent intent) {
}
/**
* Stop the service, if it was previously started. This is the same as
* calling {@link android.content.Context#stopService} for this particular service.
*
* @see #stopSelfResult(int)
*/
public final void stopSelf() {
stopSelf(-1);
}
/**
* Old version of {@link #stopSelfResult} that doesn't return a result.
*
* @see #stopSelfResult
*/
public final void stopSelf(int startId) {
if (mActivityManager == null) {
return;
}
try {
mActivityManager.stopServiceToken(
new ComponentName(this, mClassName), mToken, startId);
} catch (RemoteException ex) {
}
}
/**
* Stop the service if the most recent time it was started was
* <var>startId. This is the same as calling {@link
* android.content.Context#stopService} 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 {@link #onStart}.
*
* <p>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.</p>
*
* @param startId The most recent start identifier received in {@link
* #onStart}.
* @return Returns true if the startId matches the last start request
* and the service will be stopped, else false.
*
* @see #stopSelf()
*/
public final boolean stopSelfResult(int startId) {
if (mActivityManager == null) {
return false;
}
try {
return mActivityManager.stopServiceToken(
new ComponentName(this, mClassName), mToken, startId);
} catch (RemoteException ex) {
}
return false;
}
/**
* @deprecated This is a now a no-op, use
* {@link #startForeground(int, Notification)} instead. This method
* has been turned into a no-op rather than simply being deprecated
* because analysis of numerous poorly behaving devices has shown that
* increasingly often the trouble is being caused in part by applications
* that are abusing it. Thus, given a choice between introducing
* problems in existing applications using this API (by allowing them to
* be killed when they would like to avoid it), vs allowing the performance
* of the entire system to be decreased, this method was deemed less
* important.
*/
@Deprecated
public final void setForeground(boolean isForeground) {
Log.w(TAG, "setForeground: ignoring old API call on " + getClass().getName());
}
/**
* 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.
*
* <p>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 {@link #setForeground}
* or this modern method as appropriate:
*
* {@sample development/samples/ApiDemos/src/com/example/android/apis/app/ForegroundService.java
* foreground_compatibility}
*
* @param id The identifier for this notification as per
* {@link NotificationManager#notify(int, Notification)
* NotificationManager.notify(int, Notification)}.
* @param notification The Notification to be displayed.
*
* @see #stopForeground(boolean)
*/
public final void startForeground(int id, Notification notification) {
try {
mActivityManager.setServiceForeground(
new ComponentName(this, mClassName), mToken, id,
notification, true);
} catch (RemoteException ex) {
}
}
/**
* Remove this service from foreground state, allowing it to be killed if
* more memory is needed.
* @param removeNotification If true, the notification previously provided
* to {@link #startForeground} will be removed. Otherwise it will remain
* until a later call removes it (or the service is destroyed).
* @see #startForeground(int, Notification)
*/
public final void stopForeground(boolean removeNotification) {
try {
mActivityManager.setServiceForeground(
new ComponentName(this, mClassName), mToken, 0, null,
removeNotification);
} catch (RemoteException ex) {
}
}
/**
* Print the Service's state into the given stream. This gets invoked if
* you run "adb shell dumpsys activity service <yourservicename>".
* This is distinct from "dumpsys <servicename>", which only works for
* named system services and which invokes the {@link IBinder#dump} method
* on the {@link IBinder} interface registered with ServiceManager.
*
* @param fd The raw file descriptor that the dump is being sent to.
* @param writer The PrintWriter to which you should dump your state. This will be
* closed for you after you return.
* @param args additional arguments to the dump request.
*/
protected void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
writer.println("nothing to dump");
}
@Override
protected void finalize() throws Throwable {
super.finalize();
//Log.i("Service", "Finalizing Service: " + this);
}
// ------------------ Internal API ------------------
/**
* @hide
*/
public final void attach(
Context context,
ActivityThread thread, String className, IBinder token,
Application application, Object activityManager) {
attachBaseContext(context);
mThread = thread; // NOTE: unused - remove?
mClassName = className;
mToken = token;
mApplication = application;
mActivityManager = (IActivityManager)activityManager;
mStartCompatibility = getApplicationInfo().targetSdkVersion
< Build.VERSION_CODES.ECLAIR;
}
final String getClassName() {
return mClassName;
}
// set by the thread after the constructor and before onCreate(Bundle icicle) is called.
private ActivityThread mThread = null;
private String mClassName = null;
private IBinder mToken = null;
private Application mApplication = null;
private IActivityManager mActivityManager = null;
private boolean mStartCompatibility = false;
}
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