AlarmManager schedule Alarm on application start

Question

this is a very dumb question and I still cannot figure out how does AlarmManager work in Android. Suppose I want to schedule a repeating task every half an hour. I want to schedule it at activity onCreate(). I do something like this:

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);
        alarmMgr = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
        Intent intent = new Intent(context, AlarmReceiver.class);
        alarmIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
        alarmMgr.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,
        AlarmManager.INTERVAL_HALF_HOUR,
        AlarmManager.INTERVAL_HALF_HOUR, alarmIntent);
}

Now my question is how does OS knows that this alarm has already been scheduled? I mean it is not scheduling a new one every time activity creates, is it? Otherwise, after 10 activity launches I would get alarm every three minutes and not half an hour. Please, any Android guru, explanation about the issue.

Answer 1

Now my question is how does OS knows that this alarm has already been scheduled?

AFAIK, it looks for an existing alarm for an equivalent PendingIntent. Here, by "equivalent PendingIntent", I mean:

• the same operation (e.g., getBroadcast())
• the same ID (second parameter to getBroadcast())
• an equivalent Intent

Here, by "equivalent Intent", I mean that they match on all the routing information, which in your case is the ComponentName generated from this and AlarmReceiver.class. Extras, in particular, do not count for equivalence here.