使用Service启动AlarmManager，这样即使应用程序退出也可以正常工作。以下是示例代码：

1.创建自定义Service

public class MyAlarmService extends Service { private BroadcastReceiver receiver;

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    int AlarmType = AlarmManager.ELAPSED_REALTIME_WAKEUP;
    long TimeDelay = 5000;
    Intent intentAlarm = new Intent(this, MyAlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intentAlarm, PendingIntent.FLAG_UPDATE_CURRENT);
    AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    alarmManager.setRepeating(AlarmType, SystemClock.elapsedRealtime() + TimeDelay, TimeDelay, pendingIntent);
    return super.onStartCommand(intent, flags, startId);
}

@Override
public void onDestroy() {
    super.onDestroy();
    unregisterReceiver(receiver);
}

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

}

2.创建自定义BroadcastReceiver

public class MyAlarmReceiver extends BroadcastReceiver {

@Override
public void onReceive(Context context, Intent intent) {
    Toast.makeText(context, "Alarm worked.", Toast.LENGTH_LONG).show();
}

}

3.在主Activity中启动Service

public class MainActivity extends Activity {

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

    Intent intent = new Intent(this, MyAlarmService.class);
    startService(intent);
}

}