Android 活动启动时停止重复报警

我有这样的代码：

public class MyAlarm extends BroadcastReceiver {


@Override
public void onReceive(Context context, Intent intent) {

    AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
    alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 10000, pendingIntent);

    DBHelper dbHelper = new DBHelper(context);
    dbHelper.getWritableDatabase();

    if (dbHelper.getProfile().getHp() < dbHelper.getProfile().getHpMax()) {
        dbHelper.setHp("1", dbHelper.getProfile().getHp() + 10);
        Toast.makeText(context, "Your character gained 10HP and now has " + dbHelper.getProfile().getHp() + "HP", Toast.LENGTH_LONG).show();
    }
    else {
        Toast.makeText(context, "Your character is fully recovered", Toast.LENGTH_LONG).show();
        alarmManager.cancel(pendingIntent);
    }
}
}

我希望警报在用户启动活动时取消，并在活动暂停时启动此警报。问题是，当我启动活动时，此警报仍在运行。如何在onStart（）中停止它

    @Override
protected void onStart() {
    super.onStart();
    Intent intent = new Intent(this, MyAlarm.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 1253, intent, 0);
    AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
    alarmManager.cancel(pendingIntent);
}

    @Override
    protected void onPause() {
    super.onPause();
    setAlarm(System.currentTimeMillis() + 10000);
}

    private void setAlarm(long timeInMilis) {
    Toast.makeText(getApplicationContext(), "Regeneration activated", Toast.LENGTH_LONG).show();
    alarmManager = (AlarmManager) getSystemService((Context.ALARM_SERVICE));
    Intent intent = new Intent(this, MyAlarm.class);
    pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
    alarmManager.set(AlarmManager.RTC_WAKEUP, timeInMilis, pendingIntent);
}