调用android的AlarmManager设定闹钟，在模拟器上面运行成功，小米手机上却不行？

下面是代码

 new TimePickerDialog(ChooseTiMingTime.this, 0, new TimePickerDialog.OnTimeSetListener() {
 @Override
 public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
 Intent intent = new Intent(ChooseTiMingTime.this, AlarmTestActivity.class);
 //设置响铃时间
 Calendar calendar = Calendar.getInstance();
 // //设置年月日
 calendar.setTimeInMillis(System.currentTimeMillis());
 //设置时分
 calendar.set(Calendar.HOUR, hourOfDay);
 calendar.set(Calendar.MINUTE, minute);
                    //构造一个PendingIntent对象
                    PendingIntent pendingIntent = PendingIntent.getActivity(ChooseTiMingTime.this, 0, intent, 0);
                    //设置在规定的时间内启动组件
                    alarmManager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
                    //闹铃设置成功提示
                    Toast.makeText(ChooseTiMingTime.this, "闹铃设置成功", Toast.LENGTH_SHORT).show();
                }
            }, currentCalendar.get(Calendar.HOUR_OF_DAY), currentCalendar.get(Calendar.MINUTE), false).show();

下面是简单的dialog的activity

 //加载指定音乐
 mediaPlayer = MediaPlayer.create(AlarmTestActivity.this, R.raw.alarm);
 //设置循环播放
 mediaPlayer.setLooping(true);
 mediaPlayer.start();
 //创建一个对话框
    new AlertDialog.Builder(AlarmTestActivity.this).setTitle("闹钟").setMessage("闹钟响了，GO!GO!GO!倩楠，你要迟到了！！！！").setPositiveButton("确定",
    new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
              //停止音乐
            mediaPlayer.stop();
            //释放资源
            mediaPlayer.release();
            //结束该Activity
            finish();
        }
    }).show();