Android: How to use AlarmManager

“Some sample code” is not that easy when it comes to AlarmManager.

Here is a snippet showing the setup of AlarmManager:

AlarmManager mgr=(AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
Intent i=new Intent(context, OnAlarmReceiver.class);
PendingIntent pi=PendingIntent.getBroadcast(context, 0, i, 0);

mgr.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime(), PERIOD, pi);

In this example, I am using setRepeating(). If you want a one-shot alarm, you would just use set(). Be sure to give the time for the alarm to start in the same time base as you use in the initial parameter to set(). In my example above, I am using AlarmManager.ELAPSED_REALTIME_WAKEUP, so my time base is SystemClock.elapsedRealtime().

Here is a larger sample project showing this technique.

There are some good examples in the android sample code

.android-sdksamplesandroid-10ApiDemossrccomexampleandroidapisapp

The ones to check out are:

  • AlarmController.java
  • OneShotAlarm.java

First of, you need a receiver, something that can listen to your alarm when it is triggered. Add the following to your AndroidManifest.xml file

<receiver android:name=".MyAlarmReceiver" />

Then, create the following class

public class MyAlarmReceiver extends BroadcastReceiver { 
     @Override
     public void onReceive(Context context, Intent intent) {
         Toast.makeText(context, "Alarm went off", Toast.LENGTH_SHORT).show();
     }
}

Then, to trigger an alarm, use the following (for instance in your main activity):

AlarmManager alarmMgr = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(this, MyAlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
Calendar time = Calendar.getInstance();
time.setTimeInMillis(System.currentTimeMillis());
time.add(Calendar.SECOND, 30);
alarmMgr.set(AlarmManager.RTC_WAKEUP, time.getTimeInMillis(), pendingIntent);

.


Or, better yet, make a class that handles it all and use it like this

Bundle bundle = new Bundle();
// add extras here..
MyAlarm alarm = new MyAlarm(this, bundle, 30);

this way, you have it all in one place (don’t forget to edit the AndroidManifest.xml)

public class MyAlarm extends BroadcastReceiver {
    private final String REMINDER_BUNDLE = "MyReminderBundle"; 

    // this constructor is called by the alarm manager.
    public MyAlarm(){ }

    // you can use this constructor to create the alarm. 
    //  Just pass in the main activity as the context, 
    //  any extras you'd like to get later when triggered 
    //  and the timeout
     public MyAlarm(Context context, Bundle extras, int timeoutInSeconds){
         AlarmManager alarmMgr = 
             (AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
         Intent intent = new Intent(context, MyAlarm.class);
         intent.putExtra(REMINDER_BUNDLE, extras);
         PendingIntent pendingIntent =
             PendingIntent.getBroadcast(context, 0, intent, 
             PendingIntent.FLAG_UPDATE_CURRENT);
         Calendar time = Calendar.getInstance();
         time.setTimeInMillis(System.currentTimeMillis());
         time.add(Calendar.SECOND, timeoutInSeconds);
         alarmMgr.set(AlarmManager.RTC_WAKEUP, time.getTimeInMillis(),
                      pendingIntent);
     }

      @Override
     public void onReceive(Context context, Intent intent) {
         // here you can get the extras you passed in when creating the alarm
         //intent.getBundleExtra(REMINDER_BUNDLE));

         Toast.makeText(context, "Alarm went off", Toast.LENGTH_SHORT).show();
     }
}

What you need to do is first create the intent you need to schedule. Then obtain the pendingIntent of that intent. You can schedule activities, services and broadcasts. To schedule an activity e.g MyActivity:

  Intent i = new Intent(getApplicationContext(), MyActivity.class);
  PendingIntent pi = PendingIntent.getActivity(getApplicationContext(),3333,i,
  PendingIntent.FLAG_CANCEL_CURRENT);

Give this pendingIntent to alarmManager:

  //getting current time and add 5 seconds in it
  Calendar cal = Calendar.getInstance();
  cal.add(Calendar.SECOND, 5);
  //registering our pending intent with alarmmanager
  AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
  am.set(AlarmManager.RTC_WAKEUP,cal.getTimeInMillis(), pi);

Now MyActivity will be launched after 5 seconds of the application launch, no matter you stop your application or device went in sleep state (due to RTC_WAKEUP option).
You can read complete example code Scheduling activities, services and broadcasts #Android