Develop Reference

Android - Start background service in a correct manner

I've read the documentation about services and many examples on the web. However, most examples just include the same code and I still don't understand the life cyle of a background service completely.
Here is what I'm trying to do:
Start Activity
Activity starts a service, receiving location data
Exit Activity
Service keeps collecting
Start Activity
Bind to service and do some stuff, e.g. display some results
And this is what I've done to achive it:
Implemented a service (not an IntentService)
tried to start it in two ways:
Start the service by binding to it:
bindService(intent, myLocationService, Context.BIND_AUTO_CREATE);
This results in the service beeing created when the activity starts and beeing destroyed, when I call unbindService(...), e.g. in the onStop() method of the activity.
Start the service by creating it, explicitly:
Intent intent = new Intent(this, MyLocationService.class);
startService(intent);
This results in the service beeing created when the activity starts. When exiting the activity, the services crashes (although, I've implemented all cleaning up) and gets started again. When starting the activity again, the services starts once more, too.
So, how can I start, bind and unbind a serivce gracefully, without all that crashing and restarting behaviour?
These are the relevant code lines of the service:
public class MyLocationService extends Service {
final IBinder myServiceBinder = new MyServiceBinder();
public static class MyServiceConnection implements ServiceConnection {
MyLocationService service;
boolean bound = false;
#Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
MyServiceBinder binder = (MyServiceBinder)iBinder;
service = binder.getService();
bound = true;
}
#Override
public void onServiceDisconnected(ComponentName componentName) {
bound = false;
}
public MyLocationService getService() {
return service;
}
public boolean isBound() {
return bound;
}
}
/**
* Binder for GPSService
*/
public class MyServiceBinder extends Binder {
MyLocationService getService() {
return MyLocationService.this;
}
}
public MyLocationService() {
}
#Nullable
#Override
public IBinder onBind(Intent intent) {
return myServiceBinder;
}
}
These are the relevant code lines of the activity:
public class MyMainActivity extends AppCompatActivity {
MyLocationService.MyServiceConnection myServiceConnection;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Intent intent = new Intent(this, MyLocationService.class);
startService(intent);
}
#Override
protected void onStart() {
super.onStart();
}
#Override
protected void onResume() {
super.onResume();
Intent intent = new Intent(this, MyLocationService.class);
bindService(intent, myServiceConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onPause() {
super.onPause();
unbindService(myServiceConnection);
}
#Override
protected void onStop() {
super.onStop();
}
}

https://developer.android.com/guide/components/activities/activity-lifecycle.html
Depending on what your requirements are, should be onPause() onResume() or onStart() and onStop().
If you want the service to run in the background you could use
/**
* 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</em> 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; }
onRebind() to do something.

Android: Getting data from server to activity

My app polls data from server after it was notified by cloud messaging.
The data is fetched in GcmListenerService. My current approach is to use an Intent to transfer the data to the relevant activity via a broadcast receiver. This only works if the activity is in foreground.
How to store the data fetched by GcmListenerService such that the activity will update itself according to the fetched data as soon as it is resumed?

You could use service binding.
Declare a Binder implementation as part of your service definition:
public class MyService extends Service {
private final IBinder mBinder = new MyBinder();
// Set this field whenever you receive data from the cloud.
private ArrayList<MyDataType> latestCloudData;
public class MyBinder extends Binder {
public ArrayList<MyDataType> getLatestCloudData() {
return MyService.this.latestCloudData;
}
}
#Override
public IBinder onBind(Intent intent) {
return mBinder;
}
}
Bind and unbind to your service in your activity's onStart and onStop, respectively, by providing an implementation of ServiceConnection:
public class MyActivity extends Activity {
// Provides an interface for communicating with the service.
MyBinder mMyBinder = null;
boolean mBound = false;
#Override
protected void onStart() {
super.onStart();
// Bind to service
Intent intent = new Intent(this, MyService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop() {
super.onStop();
// Unbind from service
if (mBound) {
unbindService(mConnection);
mBound = false;
}
}
/** Defines callbacks for service binding, passed to bindService() */
private ServiceConnection mConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className,
IBinder binder) {
// Successfully bound, cast the IBinder to a MyBinder.
MyBinder myBinder = (MyBinder) binder;
// Can now use the MyBinder instance to communicate with the service.
MyActivity.this.mMyBinder = myBinder;
mBound = true;
// Use the MyBinder to get the latest cloud data from the service and update your view.
ArrayList<MyDataType> cloudData = MyActivity.this.mMyBinder.getLatestCloudData();
MyActivity.this.updateViewWithCloudData(cloudData);
}
#Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
private void updateViewWithCloudData(ArrayList<MyDataType> data) {
// Use the data to update your view here...
}
}
See the Android Developer Guide for more information about Bound Services (the example above is a modified version of the example found there).
Also note that this will only help you when your activity moves from the background to the foreground (or is recreated). If you also want to receive updates while the activity is in the foreground, you should also perform a broadcast which your activity should listen for. However, you do not need to bundle the cloud data as part of this broadcast. The broadcast can simply be a simple notification prompting the activity to query the service for the new data using MyBinder.getLatestCloudData().

Android, calling class method AFTER receiving message from service

Well, I have a service, I have an Activity. They communicate via messages (It must communicate with messages so don't tell me about Intents or other things, please).
I receive a Bundle from the Service, all ok.
Now with the Bundle i've received I want to do something. I want to call a method from "SomeClass", but I can't, because I'm inside of "IncomingHandler" class.
What's the best way to call SomeClass from inside IncomingHandler?
Thanks in advance
class SomeClass implements ServiceConnection {
class IncomingHandler extends Handler {
#Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MyService.MS_GET_SOMETHING:
Bundle received=msg.getData();
...

If you really want the activity to be calling methods on the service, its time to learn about AIDL, which allows an Activity to make function calls on a bound service via an RPC mechanism. Documentation found here.

I have implemented the feature (Service calls method in activity) like this:
Service sends a broadcast-message.
Activity has a local nested broadcastreceiver that can call a method in the parent activity.
public class MainActivity extends Activity {
private BroadcastReceiver myReceiver = null;
class _RemoteTimeTrackerReceiver extends BroadcastReceiver {
#Override
public void onReceive (Context context, Intent intent) {
// call method in activity
reloadGui();
}
}
#Override
public void onResume() {
super.onResume();
if (myReceiver == null)
{
myReceiver = new _RemoteTimeTrackerReceiver();
IntentFilter filter = new IntentFilter(Global.REFRESH_GUI);
registerReceiver(myReceiver, filter);
}
reloadGui();
}
#Override
public void onPause() {
if (myReceiver != null)
{
unregisterReceiver(myReceiver);
myReceiver = null;
}
super.onPause();
}
void reloadGui() {}

Android: Push data from service to activity

I am using ICP in order to create a communication between activity and service.
I can call service's method from activity using the interface.
My problem is that sometimes i want to push data from service to activity, I want to call activity;s method from service. for example : updateTextView(String msg);
I don't want to use broadcast because i read that it is not very performant.
I read something about some callback but I don't know how to create it and where to put it.
Thank you !

You can put a bundle you start the service with. Populate that bundle in the Service that you want to pass back to the Activity. Then pass the bundle back to the Activity.

You could try this via Handler. You create a field Handler in your activity, and other of the same class in your Service and onServiceConnected method call a Service's method setHandler. Then, you can send messages to handler field of Activity via handler of the Service.
public class mService extends Service{
private myHandler handler;
.....
public void setHandler(myHandler activityHandler){
this.handler=activityHandler;
}
}
public class Activity extends Activity{
private myHandler activityHandler;
....
public class myHandler extends Handler{
#Override
public void handleMessage(Message msg){
switch(msg.what){
//Implement this
}
}
}
private ServiceConnection mConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className,
IBinder service) {
.....
mService= binder.getService();
mBound = true;
mService.setHandler(dHandler);
}
#Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
}

Android ClassCast exception when binding to service

Ok, I'm new to android development and am trying to bind to a service so that I can call methods on the service once it's been started. The Activity and Service described below are both part of the same application so there shouldn't be any problems there, but everytime I run my app I get the following error:
java.lang.ClassCastException: android.os.BinderProxy
The line this happens on is:
LocalBinder binder = (LocalBinder) service;
My Activity code (simplified is):
public class Main extends Activity {
boolean gpsBound = false;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
/** Called whenever the activity is started. */
#Override
protected void onStart() {
super.onStart();
// Bind to GPSService
Intent i = new Intent(this, GPSService.class);
startService(i);
bindService(i, connection, Context.BIND_AUTO_CREATE);
}
/** service binding */
private ServiceConnection connection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
// After binding to GPSService get the instance of it returned by IBinder
LocalBinder binder = (LocalBinder) service;
gpsBound = true;
}
public void onServiceDisconnected(ComponentName className) {
gpsBound = false;
}
};
}
Service:
public class GPSService extends Service {
#Override
public void onCreate() {
super.onCreate();
}
#Override
public IBinder onBind(Intent i) {
// TODO Auto-generated method stub
return new LocalBinder<GPSService>(this);
}
/**
* Our implementation of LocationListener that handles updates given to us
* by the LocationManager.
*/
public class CustomLocationListener implements LocationListener {
DBHelper db;
CustomLocationListener() {
super();
}
// Overridden methods here...
}
}
And finally my LocalBinder:
/**
* A generic implementation of Binder to be used for local services
* #author Geoff Bruckner 12th December 2009
*
* #param <S> The type of the service being bound
*/
public class LocalBinder<S> extends Binder {
private String TAG = "LocalGPSBinder";
private WeakReference<S> mService;
public LocalBinder(S service){
mService = new WeakReference<S>(service);
}
public S getService() {
return mService.get();
}
}
I understand the meaning of the ClassCast Exception but cannot understand what to do! I've followed the example in the google documentation but it's still not working. Can anyone shed any light on what might be causing this?
Thanks in advance!

Delete attribute process in your AndroidManifest.xml of your service.

Had same error. I had added the android:process=":process_description" attribute in the manifest. When you add it, your service is created as separate process and hence you get instance of binderProxy (Hence the class cast exception)

If you are trying to bind to a local service than yes, you can just cast it. However if you are trying to bind to a remote (separate process) service you must use the AIDL method as prescribed in this article.
http://developer.android.com/guide/components/aidl.html

the LocalBinder passed in onServiceConnected has a generic type argument, while your local variable LocalBinder binder does not have one.
Resolve this one way or another, either by removing the generic type from the definition of LocalBinder, or by adding one to your declaration of your local variable binder in onServiceConnected
class MyBoundService extends Service{
private final IBinder mBinder = new MyBinder();
#Override
public IBinder onBind(Intent intent) {
return mBinder;
}
public class MyBinder extends Binder{
public void doStuff(){
//Stuff
}
//More Binder Methods
}
}
class MyActivity extends Activity{
private MyBinder mBinder;
#Override
protected void onStart(){
Intent intent = new Intent(this, MyBoundService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop(){
unbindService(mConnection);
}
private ServiceConnection mConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className, IBinder service) {
mBinder = (TaskBinder) service;
mBound = true;
}
#Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
private void doStuff(){
if (mBound)
mBinder.doStuff();
}
}
No real need to fiddle around with weak references and whatnot. just be sure to unbind (I didn't in the sample)
If you want to invoke service methods ASAP, just put calls in onServiceConnected, after you set mBinder. otherwise, just invoke from other callbacks (onClick events and whatnot).