Fun with alarms Part 1: Alarms without services

Overview (Video) (Source code for first part)

· Android allows you to set alarms

· When the alarm goes off, the OS sends your application an intent.

· However, receiving these intents is a bit tricky.

· Consequently, this approach is probably not sufficient for most applications.

· We’ll need to use services, which is Part 2

· Note that Handler is also used to make things happen in the future. Thus, one should consider using it instead of AlarmManager.

o Note: The Alarm Manager is intended for cases where you want to have your application code run at a specific time, even if your application is not currently running. For normal timing operations (ticks, timeouts, etc) it is easier and much more efficient to use Handler.

Starting

· Start with a new Android project

o called FunWithAlarms

o with a button and button listener, and

o TextView, called textView

· Make a new class, we’ll call OneShotAlarmReceiver, derived from android.content.BroadcastReceiver

o Note, it must be a new class. It cannot be a local class of FunWithAlarms.

o As we will see, some BroadcastReceivers can be local classes.

· In OneShotAlarmReceiver, add function onReceive(Context context, Intent intent)

· In this function, add Log.d("OneShotAlarmReceiver ","Alarm Expired");

· In the manifest, with the application section (as far as I know, everything must be in the application section), add

o <receiver android:name=". OneShotAlarmReceiver "> </receiver>

o Note, this is the name we gave our broadcast receiver

Setting the alarm

· In FunWithAlarms, within the button onClick listener add

o Intent intent = new Intent(context, OneShotAlarmReceiver.class); // again, our broadcast receiver

o PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_ONE_SHOT); // other flags make other types of alarms, like periodic alarms

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

o alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (5 * 1000), pendingIntent); // (5*1000) so the alarm will expire in 5 seconds

o Log.d(“FunWithAlarms1”,”Alarm is set”);

Run program

· Press button

· Note that all log shows things worked as expected

Problems (Video) (Source code for second part)

· How to run the main activity?

· We can’t directly access the FunWithAlarms object.

· Instead we’ll use another intent to trigger a BroadcastReceiver that is part of FunWithAlarms

o Why not make OneShotAlarmReceiver part of FunWithAlarms?

o Maybe one can, but I couldn’t get it to work.

Add BroadcastReceiver to FunWithAlarms

· In FunWithAlarms, add local class

o public BroadcastReceiver receiver=new BroadcastReceiver() {

o public void onReceive(Context context, Intent intent) {

o Log.d("FunWithAlarms ","Received TimesUp message");

o }

o };

· Register this BroadcastReceiver

o In FunWithAlarms.onCreate add

§ registerReceiver(receiver, new IntentFilter("com. FunWithAlarms.TIMESUP ")); // note that this name com. FunWithAlarms.TIMESUP must be the same as the name above (It is better to use a single string constant.).

· We must also unregister this broadcast receiver in onPause

o In FunWithAlarms, add

§ public void onPause () {

§ super.onPause();

§ Log.d(“FunWithAlarms1”,”onPause”);

§ unregisterReceiver(receiver);

§ }

· And reregister in onResume

o In FunWithAlarms, add

§ public void onPause () {

§ super.onPause();

§ Log.d(“FunWithAlarms1”,”onResume”);

§ registerReceiver(receiver, new IntentFilter("com. FunWithAlarms.TIMESUP ")); // that same constant again!

§ }

· Call this BroadcastReceiver from OneShotAlarmReceiver

o In OneShotAlarmReceiver.onReceive add

§ Intent broadcast=new Intent("com.FunWithAlarms.TIMESUP "); // the same name again, we really should use a constant!

§ context.sendBroadcast(broadcast);

· Note: now we have two BroadcastReceivers. One is registered in the manifest and one is registered in the code.

Run program

· The log shows that things run as expected

· Now test what happens if the phone sleeps before the alarm goes off. The alarm expires so that first BroadcastReceiver is called.

· But the activity is not running, so it is not called.

· In some cases, this behavior might be fine.

· However, if you want to catch this event, you must use a service