android - 使用 setExact() 在每天的特定时间触发警报

Question

我试图在每天的特定时间触发一次警报。但与所有其他人一样，我使用的是 setExact() 而不是 setRepeating()。警报在正确的时间触发。但是一旦它触发，它就会每 5 秒重复一次。我怎样才能在一天的特定时间只触发一次？这是我的代码:

主要 Activity .java:

public class MainActivity extends AppCompatActivity implements Observer {

    private AlarmManager alarmManager = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BroadcastObserver.getInstance().addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        Log.e("MainActivity", "Alarm set through observer");
        cancelAlarm();
        setAlarm();
    }

    @Override
    protected void onStart() {
        super.onStart();
        if (!checkAlarm()) {
            setAlarm();
        }

    }

    public void setAlarm() {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY, 14);
        calendar.set(Calendar.MINUTE, 13);
        calendar.set(Calendar.SECOND, 0);
        alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        Intent intent = new Intent(this, MyReceiver.class);
        intent.setAction(MyReceiver.ACTION_RECEIVER);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 1001, intent, PendingIntent.FLAG_CANCEL_CURRENT);
        alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
    }

    private boolean checkAlarm() {
        Intent intent = new Intent(this, MyReceiver.class);
        intent.setAction(MyReceiver.ACTION_RECEIVER);
        boolean isSet = PendingIntent.getBroadcast(this, 1001, intent, PendingIntent.FLAG_NO_CREATE) != null;
        Log.e("MainActivity", isSet + " :Alarm is set");
        return isSet;
    }

    @Override
    protected void onStop() {
        super.onStop();
        cancelAlarm();
    }

    private void cancelAlarm() {
        Intent intent = new Intent(this, MyReceiver.class);
        intent.setAction(MyReceiver.ACTION_RECEIVER);
        final PendingIntent pendingIntent =
                PendingIntent.getBroadcast(MainActivity.this, 1001, intent,
                        PendingIntent.FLAG_NO_CREATE);
        if (pendingIntent != null) {
            alarmManager.cancel(pendingIntent);
            pendingIntent.cancel();
        }
    }
}

广播接收者:

public class MyReceiver extends BroadcastReceiver {

    public static final String ACTION_RECEIVER = "Receiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.e("MainActivity", "triggered");
        BroadcastObserver.getInstance().updateValue(intent);
    }
}

广播观察者:

public class BroadcastObserver extends Observable {
    private static BroadcastObserver instance = new BroadcastObserver();

    public static BroadcastObserver getInstance(){
        return instance;
    }

    private BroadcastObserver(){}

    public void updateValue(Object data) {
        synchronized (this) {
            setChanged();
            notifyObservers(data);
        }
    }
}

Answer 1

once it fires it keeps on repeating itself after every 5 sec

您正在为指定日期的 14:13 设置闹钟。当警报触发时，Observer 会收到通知并设置完全相同的相同 警报(14:13)。

此时我们已经过了 14:13，所以警报会立即触发，再次通知 Observer，导致上述步骤的无限循环。

最简单的解决方案可能是在设置闹钟时检查时间，如果是过去的时间，则添加一天:

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.HOUR_OF_DAY, 14);
calendar.set(Calendar.MINUTE, 13);
calendar.set(Calendar.SECOND, 0);

if (calendar.before(Calendar.getInstance())) {
    calendar.add(Calendar.DAY_OF_YEAR, 1);
}

为避免内存泄漏，您需要在适当的时候移除Observer:

@Override
protected void onDestroy() {
    BroadcastObserver.getInstance().deleteObserver(this);
    super.onDestroy();
}

此外，在 update() 中取消警报是多余的。这不是一个重复的警报，因此在它触发后取消它是没有意义的。