Android通过如下方式实现定时任务，定时广播通知TestReceiver，测试发现当屏幕关闭时，定时任务不再执行，请问问题出在哪里。
Intent intent = new Intent("android.intent.action.EDIT");
intent.putExtra("heartType", "fix");
PendingIntent sender = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
long firstime = SystemClock.elapsedRealtime();
AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, firstime, 5 * 1000, sender);
手机测试环境：Android 4.1
代码见链接：http://pan.baidu.com/s/1bn5xOx5
