Develop Reference

The same background music playing in all activities

I use services to play background music in all activities and it works. The problem is the music continues playing even if my app is in background (when user exit with home button or back button). How can I solve this?
Services class BackgroundSoundService
public class BackgroundSoundService extends Service {
private static final String TAG = null;
MediaPlayer player;
public IBinder onBind(Intent arg0) {
return null;
}
#Override
public void onCreate() {
super.onCreate();
player = MediaPlayer.create(this, R.raw.slow_shock);
player.setLooping(true); // Set looping
player.setVolume(100,100);
}
public int onStartCommand(Intent intent, int flags, int startId) {
player.start();
return START_NOT_STICKY;
}
public void onStart(Intent intent, int startId) {
// TO DO
}
public IBinder onUnBind(Intent arg0) {
// TO DO Auto-generated method
return null;
}
public void onStop() {
}
public void onPause() {
}
#Override
public void onDestroy() {
player.stop();
player.release();
}
#Override
public void onLowMemory() {
}
}
Starting with
Intent svc = new Intent(this, BackgroundSoundService.class);
startService(svc);
Android Manifest:
<service android:enabled="true" android:name=".BackgroundSoundService" />

This is happened because the Service is still bounded in the activity. To terminate the service when multiple activity is bound to the service, you need to unbind the service from all of them as in the documentation says:
The service lifecycle—from when it's created to when it's
destroyed—can follow either of these two paths:
A started service
The service is created when another component calls startService().
The service then runs indefinitely and must stop itself by calling
stopSelf(). Another component can also stop the service by calling
stopService(). When the service is stopped, the system destroys it.
A bound service
The service is created when another component (a client) calls
bindService(). The client then communicates with the service through
an IBinder interface. The client can close the connection by calling
unbindService(). Multiple clients can bind to the same service and
when all of them unbind, the system destroys the service. The service
does not need to stop itself.
These two paths are not entirely separate. You can bind to a service
that is already started with startService(). For example, you can
start a background music service by calling startService() with an
Intent that identifies the music to play. Later, possibly when the
user wants to exercise some control over the player or get information
about the current song, an activity can bind to the service by calling
bindService(). In cases such as this, stopService() or stopSelf()
doesn't actually stop the service until all of the clients unbind.
Then call Context.stopService() to stop it:
context.stopService(new Intent(context, BackgroundSoundService.class));

Which function is called when application is removed from task manager

I need to make status of user offline. When I press home button onStop() is called, that's fine. When I press back button onDestroy() is invoked. But when I close the app from recent apps by swiping it, onStop() or onDestroy() isn't called.
I need to know when the app is closed from recent apps to do something (e.g make user offline).

Make a service :
public class MyService extends Service {
private DefaultBinder mBinder;
private AlarmManager alarmManager ;
private PendingIntent alarmIntent;
private void setAlarmIntent(PendingIntent alarmIntent){
this.alarmIntent=alarmIntent;
}
public void onCreate() {
alarmManager (AlarmManager)getSystemService(Context.ALARM_SERVICE);
mBinder = new DefaultBinder(this);
}
#Override
public IBinder onBind(Intent intent) {
return mBinder;
}
public void onTaskRemoved (Intent rootIntent){
alarmManager.cancel(alarmIntent);
this.stopSelf();
}
}
Make a custom class :
public class DefaultBinder extends Binder {
MyService s;
public DefaultBinder( MyService s) {
this.s = s;
}
public MyService getService() {
return s;
}
}
Add to your activity :
MyService service;
protected ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder binder) {
service = ((DefaultBinder) binder).getService();
service.setAlarmIntent(pIntent);
}
public void onServiceDisconnected(ComponentName className) {
service = null;
}
};
protected void onResume() {
super.onResume();
bindService(new Intent(this, MainService.class), mConnection,
Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop() {
super.onStop();
if (mConnection != null) {
try {
unbindService(mConnection);
} catch (Exception e) {}
}
}

But when I close the app from recent apps by swiping it, onStop() or onDestroy() isn't called.
Methods of Activity lifecycle that are to be called when Activity is no longer visible are not guaranteed to be called when removed from the recent tasks (treat it as "soft" version of killing an app by the system due to low memory).
I need to know when the app is closed from recent apps to do something (e.g make user offline)
I suggest one of the following:
(If applicable) use Activity's onResume()/onPause() to "make user online/offline";
use Service that sticks to the application meaning that if the app is killed after Service's onStartCommand() returns, the service will be recreated and onStartCommand() will be called again. At this point you could "make user offline". The chain of lifecycle method calls would be:
Activity's onStop() -> onDestroy()* ->
Service's onTaskRemoved()* ->
Application's onCreate() -> Service's onCreate() ->
Service's onStartCommand()
The Intent passed to the method will help you recognize which component triggered the start request:
Intent != null, meaning the request has been received from a running Activity instance
Intent = null, meaning the request has been sent by the (newly created) Application instance
* Not guaranteed to be called

No, there is no clean way to get the application termination time. But I could suggest you a dirty trick to use a service to update your application (offline functionalities) for every after n minutes.
When OS kill your application, it will remove all associated services and broadcast receiver along with it.

Android Service with MediaPlayer gets recreated or destroyed

I'm using bound service so that I am able to communicate between an activity and a service.
I'm binding to a service in onStart:
#Override
protected void onStart() {
super.onStart();
Intent bindIntent = new Intent(this, MusicService.class);
bindService(bindIntent, this, BIND_AUTO_CREATE);
}
waiting for service to bind:
#Override
public void onServiceConnected(ComponentName name, IBinder service) {
mMusicService = ((MusicService.LocalBinder) service).getService();
mMusicService.setCallback(this);
}
handling disconnect from service:
#Override
public void onServiceDisconnected(ComponentName name) {
mMusicService = null;
}
unbinding from service in onDestroy:
#Override
protected void onDestroy() {
super.onDestroy();
if (mMusicService != null && isFinishing()) {
mMusicService.setCallback(null);
unbindService(this);
}
}
My problem is that when app is minimized, onDestroy gets called immediately and then onUnbind in Service gets called and music is stopped.
Here is onUnbind method (where mPlayer is MediaPlayer):
#Override
public boolean onUnbind(Intent intent) {
mPlayer.stop();
mPlayer.release();
mPlayer = null;
return super.onUnbind(intent);
}
If I don't implement onUnbind music continues to play (sometimes and sometimes it stops after some time) and when I open the app again (from minimized applications) I am able to play another song and then those two song play at same time.
I've red couple articles about music players and services on android and I thought that this was correct approach (thinking that onDestroy will be called when OS is out of memory).
Any ideas how I can re-implement my app workflow so that I will work as expected?
EDIT
At first I thought that "Don't keep activities" under developer options is a problem, but problem is still there even if I uncheck it.
And if some code from my service is needed please say I will edit my question (there's a lot of code and I'm not sure which part is important for this issue)
SOLUTION:
startForeground(<notification id>, <notification>);
to run service even if app gets killed. And when user dismisses the notification:
stopForeground(true);
stopSelf();
More about startForeground here.

It's not obvious, but you should start a Thread that runs in background and use the service to control it's state.
A service isn't a thread that hold some run state like a thread. Unless it's an IntentService. (Correct me if I'm wrong)
While activity can (and probably will) get destroyed, your app will keep running.
Activity:
#Override
protected void onStart() {
super.onStart();
Intent intent = new Intent(this, BackgroundService.class);
startService(intent);
bindService(intent, mServiceConnection, Context.BIND_AUTO_CREATE);
finishOnPause = true;
}
#Override
protected void onStop() {
super.onStop();
unbindService(mServiceConnection);
}
Service:
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
ensureServiceThread();
if (intent != null) {
}
return START_NOT_STICKY;
}
private void ensureServiceThread() {
if (service_thread == null) {
service_thread = new ServiceThread(this);
service_thread.start();
}
}
#Override
public void onDestroy() {
stopServiceThread();
super.onDestroy();
}
private void stopServiceThread() {
if (service_thread != null) {
service_thread.interrupt();
service_thread = null;
}
}
And you should do your work inside the Thread.
If you need context, it's your Service.
If you need to do something on Main thread - create a Handler in Service.OnCreate and do a handler.postRunnable inside a worker thread safely.
What I would do is:
- Create a service
- Create a thread
- Create a media player inside a thread (if possible, otherwise on Service creation and pass it to thread)
- Inside a thread - continuously poll media player state
- On song finished send an intent to service that change track
- stop thread/service if needed.

Activity with long-lasting service in the background that will not be killed

On Android, I have an Activity called FirstActivity which starts a Service named MyService to do networking stuff in the background. The Activity and the Service communicate with each other all the time by calling methods.
Now when the user navigates from FirstActivity to SecondActivity, the background service should not be killed or re-created, but kept alive and passed to SecondActivity which will now be the one communicating with the service.
In other words, the Service shall be running as long as one of the two Activitys is running, and it should not stop while the user navigates between the two Activitys.
One of the Activitys will always be in the foreground and during this time, the service should (optimally) never get killed. I think this should not be a problem because one of those two Activitys is always active and thus Android knows the service is important and not something that must be killed.
(If there was no way to prevent Android from killing and re-creating the service from time to time, I would need a way to restore the full state of the service gracefully.)
To sum up, the Service should have the same lifespan as the two Activitys "combined". It should start with the first of them and stop not before both of them have been destroyed.
So is the following code correct for that setup and goals?
public class MyService extends Service {
public class LocalBinder extends Binder {
public MyService getService() {
return MyService.this;
}
}
...
}
public class FirstActivity extends Activity {
private MyService mMyService;
private ServiceConnection mMainServiceConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className, IBinder service) {
MyService mainService = ((LocalBinder) service).getService();
mMyService = mainService;
mMyService.setCallback(FirstActivity.this);
}
#Override
public void onServiceDisconnected(ComponentName className) {
mMyService = null;
}
};
#Override
public void onCreate(Bundle savedInstanceState) {
...
startService(new Intent(FirstActivity.this, MyService.class));
}
#Override
protected void onResume() {
super.onResume();
bindService(new Intent(FirstActivity.this, MyService.class), mMainServiceConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onPause() {
super.onPause();
if (mMainServiceConnection != null) {
unbindService(mMainServiceConnection);
}
if (mMyService != null) {
mMyService.setCallback(null);
}
if (!isUserMovingToSecondActivity) {
stopService(new Intent(FirstActivity.this, MyService.class));
}
}
#Override
public void onBackPressed() {
stopService(new Intent(FirstActivity.this, MyService.class));
super.onBackPressed();
}
...
}
public class SecondActivity extends Activity {
private MyService mMyService;
private ServiceConnection mMainServiceConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className, IBinder service) {
MyService mainService = ((LocalBinder) service).getService();
mMyService = mainService;
mMyService.setCallback(SecondActivity.this);
}
#Override
public void onServiceDisconnected(ComponentName className) {
mMyService = null;
}
};
#Override
protected void onResume() {
super.onResume();
bindService(new Intent(SecondActivity.this, MyService.class), mMainServiceConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onPause() {
super.onPause();
if (mMainServiceConnection != null) {
unbindService(mMainServiceConnection);
}
}
#Override
protected void onDestroy() {
...
stopService(new Intent(SecondActivity.this, MyService.class));
}
...
}
Is this the best way to guarantee a long-lasting service in the background of the Activitys that will not be killed or re-created?
What about Context.BIND_AUTO_CREATE? Is it correct to have this flag set here? What about Context.BIND_ADJUST_WITH_ACTIVITY and Context.BIND_WAIVE_PRIORITY -- do I need these?

(Many thanks to #corsair992 for his useful pointers!)
If the activities are always called in that order (i.e. FirstActivity starts SecondActivity, and never the other way around, then you should, basically, attempt to "tie" the Service's life-cycle to FirstActivity's lifecycle.
In general (see caveats later), this means:
Call startService() in FirstActivity.onCreate().
Call stopService() in FirstActivity.onDestroy().
Call bindService()/unbindService() in the onStart()/onStop() methods of both Activities (to get access to the Binder object, and be able to call methods on it).
A service started this way will be alive until stopService() is called and every client unbinds, see Managing the Lifecycle of a Service:
These two paths are not entirely separate. That is, you can bind to a
service that was already started with startService(). (...) In cases like this, stopService() or
stopSelf() does not actually stop the service until all clients
unbind.
and:
When the last client unbinds from the service, the system destroys the
service (unless the service was also started by startService()).
With this basic strategy, the Service will live as long as FirstActivity is around (i.e. it is not destroyed). However, an important point still remains: in the event of a configuration change (e.g. a screen rotation) that is not handled explicitly will cause the activity to restart itself, and the service will be destroyed (since we're calling stopService() in onDestroy()).
To prevent this, you can check isChangingConfigurations() before actually stopping the service (since an onDestroy() callback occurring due to this reason means that although this particular instance of the Activity is being destroyed, it will be recreated afterwards.
Hence, the full solution would be something like:
public class FirstActivity extends Activity
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
startService(new Intent(this, MyService.class));
}
private ServiceConnection mServiceConnection = new ServiceConnection() { ... }
#Override
protected void onStart() {
super.onStart();
bindService(new Intent(this, MyService.class), mServiceConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop() {
unbindService(mServiceConnection);
super.onStop();
}
#Override
protected void onDestroy() {
if (!isChangingConfigurations())
stopService(new Intent(this, MyService.class));
super.onDestroy();
}
While SecondActivity would only implement the onStart()/onStop() methods (in the same way).
A couple of notes about your particular implementation:
It's not necessary to override onBackPressed(), since if the activity is destroyed the necessary lifecycle methods will be called (plus, it could be finished without pressing the back button, for example if calling finish() on it).
Stopping the service in onDestroy() instead of onPause() saves you from having to check for isUserMovingToSecondActivity.

How to make a started service continue after the last bound services un-binds

I would like to have a service (doing occasional monitoring) be active continuously. I plan to start it by listening to a BOOT_COMPLETE, which I believe makes it a "Started Service". I want a UI application to bound to it, which is working and documented. However, after the binding activity is destroyed, the Service dies because it's "unbound from all clients".
Is there a way to have a started service allow binding and still continue after the last bound services un-binds?
Returning true from onUnbind() wouldn't help, as the service should continue to be active even if no additional binder exist.

In Android, services are started in one of two ways - through the startService(Intent i) method, or the bindService(Intent i). The method used to start the service determines whether it is started or bound. A service can be started, then bound to a client - or bound and then have calls to start sent to it (it doesn't restart if already started).
As you mention listening for BOOT_COMPLETE, I assume this is an action for an Intent, which is sent via a Broadcast object. This means that you can create an IntentFilter object with the BOOT_COMPLETE action added to it via the addAction(String action) method. Then a BroadcastReceiver object can be created, which upon receiving an intent with an action of BOOT_COMPLETE can then call the startService(Intent i) method (this is done by overriding the onReceive(Context context, Intent intent) method).
If you call startService(Intent i) when the Intent is received, then the service will be a started service. This means that it will only stop when a call to stopService(Intent i) is made by the app, or if the service calls the stopSelf() method. It can be bound and unbound from by multiple activities during the time it is running, and it will not stop (as it is started, not bound).
Here is an example of this, using two Activity objects and a Service:
Activity 1 (first activity of your app):
public class ServiceActivity extends Activity {
private IntentFilter filter = new IntentFilter();
private BroadcastReceiver receiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if(action.equals(BOOT_COMPLETE) {
startService(new Intent(ServiceActivity.this, MyService.class));
}
}
};
#Override
protected void onStart() {
super.onStart();
filter.addAction(BOOT_COMPLETE);
registerReceiver(receiver, filter);
}
#Override
protected void onStop() {
super.onStop();
unregisterReceiver(receiver);
}
//Some other code
}
Activity 2 (used at some point after activity 1):
public class AnotherActivity extends Activity {
private MyService service;
private ServiceConnection connection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName name, IBinder service) {
service = ((MyService.MyBinder)service).getService();
}
#Override
public void onServiceDisconnected(ComponentName name) {
service = null;
}
};
#Override
protected void onStart() {
super.onStart();
bindService(new Intent(this, MyService.class), connection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop() {
super.onStop();
unbindService(connection);
}
//Some other code
}
Service:
public class MyService extends Service {
private MyBinder binder = new MyBinder();
#Override
public IBinder onBind(Intent intent) {
return binder;
}
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
super.onStartCommand(intent, flags, startId);
return START_STICKY;
}
//Some other code
final class MyBinder extends Binder {
MyService getService() {
return MyService.this;
}
}
Final notes
To be able to use the service as bound, you need to override the onBind(Intent intent) method, and return an instance of binder MyBinder. Not doing so will result in not being able to bind (the binding sets the service variable by using the getService() method defined in MyBinder).
The BroadcastReceiver must alwasy be unregistered when the Activity it's in closes, as it would be leaked otherwise. That is why in the example, I have registered and unregistered in the onStart() and onStop() methods respectively. Using onDestroy() to unregister is not recommended as it is not always called.
The MyService object that is used when binding must also be unbound when it's Activity closes, as it too can be leaked. It is set to null when onServiceDisconnected(ComponentName name) is called for garbage collecting.
Sources for further reading
https://developer.android.com/reference/android/content/BroadcastReceiver.html
https://developer.android.com/reference/android/app/Activity.html
https://developer.android.com/reference/android/app/Service.html
https://developer.android.com/reference/android/content/ServiceConnection.html