Services with Alarms

Overview (Video for part 1) (Source code for part 1)

· A service is required for an alarm to be processed when the system is sleeping.

· The idea is as follows

o The activity starts the service. A button triggers the service to set the alarm

o The alarm calls the OneShotAlarmReceiver,

o which calls a BroadcastReceiver that is part of the service

o Since the service is always able to receive broadcasts, it will be triggered even if the system is sleeping

· One complication is that we need to make sure that the system stays awake long enough to call the service.

Merge FunWithLocalServices and FunWithAlarms1

· Start with a service developed in the FunWithLocalServices tutorial

· Open the FunWithAlarms1 files for reference

· Merge FunWithLocalServices and FunWithAlarms1

o Make new class OneShotAlarmReceiver

§ Same as in FunWithAlarms1

§ onReceive with (note new name of action is changed to com.FunWithServices.MyService.TIMESUP

· Log.d("OneShotAlarmReceiver","Alarm Expired");

· Intent broadcast=new Intent("com.FunWithServices.MyService.TIMESUP");

· context.sendBroadcast(broadcast);

·

o In manifest,

§ add entry for receiver OneShotAlarmReceiver

o In MyService, add broadcast receiver

§ From FunWithAlarms1, copy public BroadcastReceiver receiver=new BroadcastReceiver() {…

o In MyService, add function to set the alarm and register the BroadcastReceiver

§ public void startAlarm()

§ {

§ registerReceiver(receiver, new IntentFilter("com.FunWithServices.MyService.TIMESUP"));

§ Intent intent = new Intent(this, OneShotAlarmReceiver.class);

§ PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_ONE_SHOT);

§ AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

§ alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (5 * 1000), pendingIntent);

§ Log.d("MyService","Alarm is set");

§ }

o In MyService.onDestroy(), add

§ unregisterReceiver(receiver);

o In FunWithLocalServices, call startAlarm from button onClickListener

§ Add myService.startAlarm();

· Run

Problem with sleeping (Video for part 2) (Source code for part 2)

· When an activity or service is running, the system might sleep at any time

· In order to keep the system awake, WakeLocks are used

· So, when the alarm goes off and the service’s broadcast receiver is triggered, it should set a WakeLock.

· The alarm’s BroadcastReceiver does not need a WakeLock, the AlarmManager keeps a WakeLock so the system does not sleep before the BroadcastReceiver.onReceive is complete

· However, the system is allowed to sleep as soon as the alarms BroadcastReceiver is finished.

· It might go to sleep before the service is able set its WakeLock

· We need to call a WakeLock from the alarm’s BroadcastReceiver.onReceive, but then release it from the services BroadcastReceiver.

· One way to solve this is to make a class with static member variables and functions.

MyStaticWakeLock class

· Make new class call MyStaticWakeLock

o public class MyStaticWakeLock {

o private static PowerManager.WakeLock wl = null;

o public static void lockOn(Context context) {

o PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);

o if (wl== null)

o wl = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK, "MyStaticWakeLock");

o wl.acquire();

o }

o public static void lockOff(Context context) {

o PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);

o if (wl != null)

o wl.release();

o }

o }

· Note, this class has two functions, one for setting the WakeLock and one for releasing

· In OneShotAlarmReceiver.onReceive, add

o MyStaticWakeLock.lockOn();

· At the end of MyService.receiver.onReceive(), add

o MyStaticWakeLock.lockOff();

· Run