AlarmManager 有时会延迟触发，或者根本不会触发

Question

I have a simple AlarmManager app which sends me an e-mail every 30 minutes, but it is not working properly. Sometimes it delays and sometimes it doesn't send anything at all. Can someone explain why this is happening?

MainActivity class:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    AlarmManager alarmMgr = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    Intent intent = new Intent(this, MyAlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
    alarmMgr.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() + AlarmManager.INTERVAL_HOUR, AlarmManager.INTERVAL_HALF_HOUR, pendingIntent);
}

MyAlarmReceiver onReceive method

private FusedLocationProviderClient fusedLocationClient;

@Override
public void onReceive(Context context, Intent intent) {
    Toast.makeText(context, "Alarm went off", Toast.LENGTH_SHORT).show();
    fusedLocationClient = LocationServices.getFusedLocationProviderClient(context);
    fusedLocationClient.getLastLocation().addOnSuccessListener(new OnSuccessListener<Location>() {
        @Override
        public void onSuccess(Location location) {
            if(location != null)
            {
                SimpleDateFormat formatter = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss");
                Date date = new Date();
                sendMail(location.getLongitude()+"", location.getLatitude()+"", formatter.format(date));
            }
        }
    });
}

Answer 1

Change the alarmMgr.setInexactRepeating for alarmMgr.setRepeating as you are using inexact alarms:

These alarms are more power-efficient than the strict recurrences traditionally supplied by setRepeating(int, long, long, PendingIntent), since the system can adjust alarms' delivery times to cause them to fire simultaneously, avoiding waking the device from sleep more than necessary.

Your alarm's first trigger will not be before the requested time, but it might not occur for almost a full interval after that time.

Answer 2

In your class code.

public class Alarm extends BroadcastReceiver 
{    
@Override
public void onReceive(Context context, Intent intent) 
{   
    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "");
    wl.acquire();

    // Put here YOUR code.

   // wl.release();
}

public void setAlarm(Context context)
{
    AlarmManager am =( AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
    Intent i = new Intent(context, Alarm.class);
    PendingIntent pi = PendingIntent.getBroadcast(context, 0, i, 0);
    am.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), 1000 * 60 * 
 10, pi); // Millisec * Second * Minute
}

public void cancelAlarm(Context context)
{
    Intent intent = new Intent(context, Alarm.class);
    PendingIntent sender = PendingIntent.getBroadcast(context, 0, intent, 0);
    AlarmManager alarmManager = (AlarmManager) 
 context.getSystemService(Context.ALARM_SERVICE);
    alarmManager.cancel(sender);
 }
}

then set alarm service

public class YourService extends Service
{
Alarm alarm = new Alarm();
public void onCreate()
{
    super.onCreate();       
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) 
{
    alarm.setAlarm(this);
    return START_STICKY;
}

@Override        
public void onStart(Intent intent, int startId)
{
    alarm.setAlarm(this);
}

@Override
public IBinder onBind(Intent intent) 
{
    return null;
 }
}

documentation [ https://developer.android.com/training/scheduling/alarms]