Best moment/location for setting an AlarmManager

Question

My application shows content for a site that also has a notification system. I want to show if there are new notifications, and I am using an AlarmManager that calls an IntentService.

My question is: where should I start/register this AlarmManager? I've put it in the onCreate() of my activity just for proof-of-concept (and its working fine, thank you very much :) ), but if you would start that activity twice, you would get multiple alarms.

The only possible solution I've come up with is this, but I don't know if this would be best practice

• Start the manager in an onCreate() if the preference "alarm started" is false
• Set some variable that it is started in preferences.

Now if the alarm stops for some reason, there's no way to restart it. So, a variation would be:

• Always call cancel in the onCreate()
• And then always set the Alarm.

This seems like a common pattern: Wanting to periodically get information with an alarm, and not setting that alarm more then once. How should I do this? When, where and how to register the alarm?

Also, continueing on @Zelimir 's comment: can you check if a certain alarm is allready set?

Ideally, the alarm would be set regardless of the activity being started or not of course, but that might be another thing.

For completeness, this is the code I'm currently using to start the alarm:

AlarmManager alMan   = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
Intent i             = new Intent(this, CommentService.class);
PendingIntent penInt = PendingIntent.getService(this, 0, i, 0);

alMan.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                          SystemClock.elapsedRealtime(), 
                          AlarmManager.INTERVAL_FIFTEEN_MINUTES, 
                          penInt);

For even more completeness, the app description / situation.
The app is basically showing blogs (journals if you will) from a certain page. It has activities for adding entry, viewing entries, adding comments, etc. On the 'mother' site there is an option to recieve notifications (like the number you see here on SO too when you get a message). I want to show if there are new messages, and so retrieve them every xx minutes. It would be shown in the notificationbar for now, but it might feed some sort of widget later.

If you need more info: the app is called Androblip and it supports a site called blipfoto.com

Answer 1

When, where and how to register the alarm?

That is impossible to answer in the abstract. It depends entirely upon what the business rules are for your app, which you declined to supply in your question.

If the monitoring is to be happening all the time, a typical pattern is to register the alarm:

• in onCreate() of your main activity for the very first run of your app
• in a BOOT_COMPLETED BroadcastReceiver, to handle reboots, which wipe the AlarmManager roster

can you check if a certain alarm is allready set?

No, but you can cancel it without issue. Just create an equivalent PendingIntent and call cancel() on the AlarmManager.