Question

I changed AlarmController.java in ApiDemo a little bit, so I want the alarm not to go off when the phone is sleeping by using AlarmManager.RTC.

        Intent intent = new Intent(AlarmController.this, RepeatingAlarm.class);
        PendingIntent sender = PendingIntent.getBroadcast(AlarmController.this,
                0, intent, 0);

        // We want the alarm to go off 30 seconds from now.
        long firstTime = SystemClock.elapsedRealtime();
        firstTime += 15*1000;

        // Schedule the alarm!
        AlarmManager am = (AlarmManager)getSystemService(ALARM_SERVICE);
        am.setRepeating(AlarmManager.RTC, //AlarmManager.ELAPSED_REALTIME_WAKEUP,
                        firstTime, 15*1000, sender);

The receiver code is like below:

public class RepeatingAlarm extends BroadcastReceiver
{
    @Override
    public void onReceive(Context context, Intent intent)
    {
        Log.d("DEBUG", "In RepeatingAlarm.onReceive, intent=" + intent);
        Toast.makeText(context, R.string.repeating_received, Toast.LENGTH_SHORT).show();
    }
}

I ran the modified app, but I still see many log messages as below after the phone wento sleep (the screen was black):

D/DEBUG ( 1390): In RepeatingAlarm.onReceive, intent=Intent { flg=0x4 cmp=com.example.android.apis/.app.RepeatingAlarm (has extras) }

This means the flag AlarmManager.RTC didn’t work. Can someone tell me why?

Thanks.

Answer 1

Since you are using elapsedRealtime to get the alarm start time, I think you need to use the ELAPSED_REALTIME flag instead of the RTC flag.

My guess is that the alarm manager is thinking it’s missed a ton of alarms because you are using the RTC flag which means the alarm manager is expecting you to send a time value in milliseconds since Jan 1st 1970, but instead you are sending elapsed milliseconds since the device booted, which is going to be a much much smaller number.

If you use the RTC flags you need to use System.currentTimeMillis() or get the time in milliseconds from a Java Date or Calendar object. If you use ELAPSED_REALTIME flags then you need to use SystemClock.elapsedRealtime().