Alarm manager is the way to go - the tricky part is to keep the phone awake after the alarm manager receiver returns. So
setup an alarm (notice you should also register an "On Boot completed" receiver to set up the alarm after a reboot - your alarms do not survive a reboot) :
Intent monitoringIntent = new Intent(context, YourReceiver.class);
monitoringIntent.setAction("your action");
PendingIntent pi = PendingIntent.getBroadcast(context, NOT_USED,
monitoringIntent, PendingIntent.FLAG_UPDATE_CURRENT);
AlarmManager am = (AlarmManager)
context.getSystemService(Context.ALARM_SERVICE);
// here is the alarm set up
am.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,
SystemClock.elapsedRealtime() + INITIAL_DELAY,
INTERVAL_BETWEEN_ALARMS, pi);
receive it - the receiver holds a WakeLock in its onReceive() which never fails :
public abstract class YourReceiver extends BroadcastReceiver {
@Override
final public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if ("your action".equals(action)) {
// monitoring - got broadcast from ALARM
try {
d("SS : " + new Signal().getSignalStrength(context));
} catch (InterruptedException e) {
e.printStackTrace();
}
// Actu8ally the lines above will ANR
// I did it with WakefulIntentService :
// WakefulIntentService.sendWakefulWork(
// context, YourWakefulService.class);
// Will be posting it asap
} else {
w("Received bogus intent : " + intent);
return;
}
}
}
If you are lucky (yourRetrieveSignal() is fast enough) this will work, otherwise you will need a (Wakeful)IntentService pattern in your receiver.
The WakefulIntentService will take care of the wake lock (if you want to avoid a dependency have a look here) - EDIT : keep in mind you can't define listeners in an intent service - see here.
If the receiver ANRs on you, you have to try the WakefulIntentService pattern. In either case you might use this :
This proved the most difficult part actually :
class Signal {
static volatile CountDownLatch latch; //volatile is an overkill quite probably
static int asu;
private final static String TAG = Signal.class.getName();
int getSignalStrength(Context ctx) throws InterruptedException {
Intent i = new Intent(TAG + ".SIGNAL_ACTION", Uri.EMPTY, ctx,
SignalListenerService.class);
latch = new CountDownLatch(1);
asu = -1;
ctx.startService(i);
Log.d(TAG, "I wait");
latch.await();
ctx.stopService(i);
return asu;
}
}
where :
public class SignalListenerService extends Service {
private TelephonyManager Tel;
private SignalListener listener;
private final static String TAG = SignalListenerService.class.getName();
private static class SignalListener extends PhoneStateListener {
private volatile CountDownLatch latch;
private SignalListener(CountDownLatch la) {
Log.w(this.getClass().getName(), "CSTOR");
this.latch = la;
}
@Override
public void onSignalStrengthChanged(int asu) {
Signal.asu = asu;
latch.countDown();
}
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.w(TAG, "Received : " + intent.getAction());
Tel = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
listener = new SignalListener(Signal.latch);
@SuppressWarnings("deprecation")
final int listenSs = PhoneStateListener.LISTEN_SIGNAL_STRENGTH;
Tel.listen(listener, listenSs);
return START_STICKY;
}
@Override
public void onDestroy() {
Log.w(TAG, "onDestroy");
Tel.listen(listener, PhoneStateListener.LISTEN_NONE);
super.onDestroy();
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
}
This is working code (but not the pinnacle of elegance admittedly - comments/corrections welcome). Do not forget to register your services in the manifest and acquire permissions.
EDIT 2013.07.23 : I did not use the onReceive - if you use it it will ANR - this is working code if you use a WakefulIntentService in onReceive and in there you call SignalListenerService.
WakeLockis not affected by the power button. – Waxbill