AlarmManager未在android上启动

我想在android上设置一个警报，但它不工作，这是我的代码。。 我使用挂起意图在特定时间启动警报，但当我在设备上运行应用程序时，它不会启动

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

    Intent alarmIntent = new Intent(MainActivity.this, AlarmReceiver.class);
    pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, alarmIntent, 0);

    findViewById(R.id.startAlarm).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);


            Calendar calendar = Calendar.getInstance();
            calendar.setTimeInMillis(System.currentTimeMillis());
            calendar.set(Calendar.HOUR_OF_DAY, 16);
            calendar.set(Calendar.MINUTE, 39);

            /* Repeating on every 20 minutes interval */
            manager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                    1000 * 60 * 20, pendingIntent);

            Toast.makeText(MainActivity.this, "Alarm Set", Toast.LENGTH_SHORT).show();
        }
    });

    findViewById(R.id.stopAlarm).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
            manager.cancel(pendingIntent);
            Toast.makeText(MainActivity.this, "Alarm Canceled", Toast.LENGTH_SHORT).show();
        }
    });
}

我是android新手，请帮助我。 这是我的接受者课程

public class AlarmReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // For our recurring task, we'll just display a message
        Toast.makeText(context, "I'm running", Toast.LENGTH_SHORT).show();
    }
}

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你在舱单上声明你的接收人了吗

      <receiver android:name="myPackage.AlarmReceiver"
                android:enabled="true" >
      </receiver>

是的，我确实声明了它。我已经试用了您的代码，并添加了以下行以使其正常工作：calendar.setTimeZone（TimeZone.getDefault（））；请记住，setrepeating并没有在您定义的时间精确设置警报（只需再等几秒钟，等待祝酒词-在我的例子中，它显示得太晚了10秒）