See below for my original answer - that pattern has worked well, but recently I've started using a different approach to Service/Activity communication:
- Use a bound service which enables the Activity to get a direct
reference to the Service, thus allowing direct calls on it, rather
than using Intents.
Use RxJava to execute asynchronous operations.
If the Service needs to continue background operations even when no
Activity is running, also start the service from the Application
class so that it does not get stopped when unbound.
The advantages I have found in this approach compared to the startService()/LocalBroadcast technique are
- No need for data objects to implement Parcelable - this is particularly important to me as I am now sharing code between Android and iOS (using RoboVM)
- RxJava provides canned (and cross-platform) scheduling, and easy composition of sequential asynchronous operations.
- This should be more efficient than using a LocalBroadcast, though the overhead of using RxJava may outweigh that.
Some example code. First the service:
public class AndroidBmService extends Service implements BmService {
private static final int PRESSURE_RATE = 500000; // microseconds between pressure updates
private SensorManager sensorManager;
private SensorEventListener pressureListener;
private ObservableEmitter<Float> pressureObserver;
private Observable<Float> pressureObservable;
public class LocalBinder extends Binder {
public AndroidBmService getService() {
return AndroidBmService.this;
}
}
private IBinder binder = new LocalBinder();
@Nullable
@Override
public IBinder onBind(Intent intent) {
logMsg("Service bound");
return binder;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
return START_NOT_STICKY;
}
@Override
public void onCreate() {
super.onCreate();
sensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
Sensor pressureSensor = sensorManager.getDefaultSensor(Sensor.TYPE_PRESSURE);
if(pressureSensor != null)
sensorManager.registerListener(pressureListener = new SensorEventListener() {
@Override
public void onSensorChanged(SensorEvent event) {
if(pressureObserver != null) {
float lastPressure = event.values[0];
float lastPressureAltitude = (float)((1 - Math.pow(lastPressure / 1013.25, 0.190284)) * 145366.45);
pressureObserver.onNext(lastPressureAltitude);
}
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
}, pressureSensor, PRESSURE_RATE);
}
@Override
public Observable<Float> observePressure() {
if(pressureObservable == null) {
pressureObservable = Observable.create(emitter -> pressureObserver = emitter);
pressureObservable = pressureObservable.share();
}
return pressureObservable;
}
@Override
public void onDestroy() {
if(pressureListener != null)
sensorManager.unregisterListener(pressureListener);
}
}
And an Activity that binds to the service and receives pressure altitude updates:
public class TestActivity extends AppCompatActivity {
private ContentTestBinding binding;
private ServiceConnection serviceConnection;
private AndroidBmService service;
private Disposable disposable;
@Override
protected void onDestroy() {
if(disposable != null)
disposable.dispose();
unbindService(serviceConnection);
super.onDestroy();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this, R.layout.content_test);
serviceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
logMsg("BlueMAX service bound");
service = ((AndroidBmService.LocalBinder)iBinder).getService();
disposable = service.observePressure()
.observeOn(AndroidSchedulers.mainThread())
.subscribe(altitude ->
binding.altitude.setText(
String.format(Locale.US,
"Pressure Altitude %d feet",
altitude.intValue())));
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
logMsg("Service disconnected");
}
};
bindService(new Intent(
this, AndroidBmService.class),
serviceConnection, BIND_AUTO_CREATE);
}
}
The layout for this Activity is:
<?xml version="1.0" encoding="utf-8"?>
<layout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.controlj.mfgtest.TestActivity">
<TextView
tools:text="Pressure"
android:id="@+id/altitude"
android:gravity="center_horizontal"
android:layout_gravity="center_vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
</layout>
If the service needs to run in the background without a bound Activity it can be started from the Application class as well in OnCreate() using Context#startService().
My Original Answer (from 2013):
In your service: (using COPA as service in example below).
Use a LocalBroadCastManager. In your service's onCreate, set up the broadcaster:
broadcaster = LocalBroadcastManager.getInstance(this);
When you want to notify the UI of something:
static final public String COPA_RESULT = "com.controlj.copame.backend.COPAService.REQUEST_PROCESSED";
static final public String COPA_MESSAGE = "com.controlj.copame.backend.COPAService.COPA_MSG";
public void sendResult(String message) {
Intent intent = new Intent(COPA_RESULT);
if(message != null)
intent.putExtra(COPA_MESSAGE, message);
broadcaster.sendBroadcast(intent);
}
In your Activity:
Create a listener on onCreate:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
super.setContentView(R.layout.copa);
receiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String s = intent.getStringExtra(COPAService.COPA_MESSAGE);
// do something here.
}
};
}
and register it in onStart:
@Override
protected void onStart() {
super.onStart();
LocalBroadcastManager.getInstance(this).registerReceiver((receiver),
new IntentFilter(COPAService.COPA_RESULT)
);
}
@Override
protected void onStop() {
LocalBroadcastManager.getInstance(this).unregisterReceiver(receiver);
super.onStop();
}
