I have a Service "GroupsTaskAlarmChecker" that is called every 20 seconds by AlarmManager in onCreate of Groups.class activity this way:
int seconds = 20;
           Intent myIntent = new Intent(Groups.this, GroupsTaskAlarmChecker.class);
           pendingIntent = PendingIntent.getService(Groups.this, 0, myIntent, 0);
           AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
           Calendar calendar = Calendar.getInstance();
           calendar.setTimeInMillis(System.currentTimeMillis());
           calendar.add(Calendar.SECOND, 10);
           alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), seconds * 1000, pendingIntent);
This works perfectly. But I need to do that when device boot. Then I know I have to make AndroidManifest like this:
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
 <receiver android:name=".ReceiverBoot">
        <intent-filter>
            <action android:name="android.intent.action.BOOT_COMPLETED">
            <category android:name="android.intent.category.HOME">
        </category></action></intent-filter>
    </receiver>
and then mi broadcastReceiver like this:
 public class ReceiverBoot extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
    int seconds = 20;
        Intent myIntent = new Intent(context, GroupsTaskAlarmChecker.class);
        pendingIntent = PendingIntent.getService(context, 0, myIntent, 0);
        AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.add(Calendar.SECOND, 10);
        alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), seconds * 1000, pendingIntent);
    }
}
but inside this onReceive I dont know how can I do the same that I did before (with intent and alarmManager to start the service each 20 seconds). Error in this line:
 AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
Is possible that I can't make an AlarmManager inside BroadcastReceiver?
I thank you all, I am an Android begginer and I need your help. Sorry for my english ;)