Android控制器如何实现包含Runnable Observable的Observer

Question

我正在写一个Cowndown计时器，我有一个countdowntimerController，它实现了Observer接口。它有一个名为countdown的内部类，它扩展了Observable类并实现了Runnable接口。但是，当runnable完成时，我的控制器不会收到通知。以下是我的代码，请告诉我哪里出错了。附：既然Observer在Observable中，我使用了countdown.addObserver（this），那会是问题吗？

public class CountdownTimerController extends ActivityController implements Observer {
    private Handler handler = new Handler(); 
    private void startTimer(int posi) {
        /* some countdown timer codes */
        Countdown countdown = new Countdown();
        countdown.addObserver(this);
       handler.post(countdown);
    }
    public void update(Observable arg0, Object arg1) {
        // TODO Auto-generated method stub
        Log.d("countdownController", "update");
    }
    private class Countdown extends Observable implements Runnable {
        //private Handler handler = new Handler();      
        public void run() {
            long millis = countdownTime - (System.currentTimeMillis() - startTime) + pausedTime;
            if(millis <=0) {
                onFinish();
                return;
            }
            /* time calculation logic */
            handler.postDelayed(this, 100);
        }

        public void onFinish(){
            notifyObservers();
            handler.removeCallbacks(this);
        }
    };
}