計時器任務沒有準確執行

我試圖執行一個基本的任務，旋轉畫布20秒，使用計時器秒，但它似乎並沒有正常工作，其落後。例如，如果我每50毫秒將矩形旋轉0.3度，則它應該在第二秒內旋轉6度，但情況並非如此。它旋轉真的很慢。這裏是我的示例代碼：計時器任務沒有準確執行

//Code for update task 
class UpdateTimeTask extends TimerTask { 

     public void run() { 
       hndView.post(new Runnable() { 
        public void run() { 
          hndView.invalidate(); //this code invalidates custom view that calls onDraw to draw rotated hand 
        } 
       }); 
     } 
} 


//Code for onDraw method of custom view that needs to be update 
@Override 
protected void onDraw(Canvas canvas){ 

    super.onDraw(canvas); 

    //ang is angle to rotate and inc is float value of 0.3 degree to be incremented 
    ang = ang + inc; 
    if (ang >= 360) ang = ang - 360; 
    canvas.rotate(ang, canvas.getWidth()/2, canvas.getHeight()/2); 
    canvas.drawRect((canvas.getWidth()/2 - 2), (canvas.getHeight()/2 - 125), (canvas.getWidth()/2 + 2), (canvas.getHeight()/2 + 10), mTextPaint); 
    canvas.restore(); 

} 

//code to schedule task 
Timer timer = new Timer(); 
UpdateTimeTask tt = new UpdateTimeTask(); 
timer.schedule(tt, 0, 50);

任何人都可以請告訴我我在做什麼錯在這裏？我應該使用不同的方法來執行此任務嗎？因爲它很難相信你不可能在一秒內有簡單的矩形平滑旋轉20次。

來源

2011-02-04 Parashar