Posted by: tigerz on March 6, 2010

在 Android 平臺上，介面元素不能在定時器的響應函式裡重新整理。

以下這段程式碼中，mButton 的文字並不變化。

public 
    private Button mButton;
    private Timer mTimer;
    private TimerTask mTimerTask;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super
 
.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mButton = (Button) findViewById(R.id.Button01);

        mTimer = new Timer();

        mTimerTask = new TimerTask() {

            @Override
            public void run() {
                Log.d(, "timer");
                Calendar cal = Calendar.getInstance();
                mButton.setText(cal.toString());
            }
        };

        mTimer.schedule(mTimerTask, 1000
 
, 1000);
    }
}

在 Android 平臺上，UI 單元必須在 Activity 的 context 裡重新整理。 為了達到想要的效果，可以使用 Message Handler。在定時器響應函式裡傳送條訊息，在 Activity 裡響應訊息並更新文字。

public 
    protected static final int UPDATE_TEXT = 0;
    private Button mButton;
    private Timer mTimer;
    private TimerTask mTimerTask;
    private Handler mHandler;


    /** Called when the activity is first created. */
 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mButton = (Button) findViewById(R.id.Button01);

        mTimer = new Timer();

        mHandler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                switch (msg.what){
                case UPDATE_TEXT:
                    Calendar cal = Calendar.getInstance();
                    mButton.setText(cal.toString());
                    break;
                }
            }
        };

        mTimerTask = new TimerTask() {

            @Override
            public void run() {
                Log.d(, "timer");
                mHandler.sendEmptyMessage(UPDATE_TEXT);
/*              
                // It doesn't work updating the UI inside a timer.
                Calendar cal = Calendar.getInstance();
                mButton.setText(cal.toString());
*/          
                }
        };

        mTimer.schedule(mTimerTask, 1000, 1000);
    }
}