Android利用SurfaceView实现简单计时器

public TestView(Context context) { 
  super(context); 
  surfaceHolder = getHolder(); 
  surfaceHolder.addCallback(this); 
  countThread = new CountThread(surfaceHolder); 
} 
 
public TestView(Context context, AttributeSet attributeSet) { 
  super(context, attributeSet); 
  surfaceHolder = getHolder(); 
  surfaceHolder.addCallback(this); 
  countThread = new CountThread(surfaceHolder); 
} 

@Override 
    public void run() { 
      Canvas canvas = null; 
      int pivotX = getResources().getDisplayMetrics().widthPixels / 2; 
      RectF rectF = new RectF(pivotX - 300, pivotX - 300, pivotX + 300, pivotX + 300); 
      while (!isStop) { 
        try { 
          canvas = surfaceHolder.lockCanvas(); 
          canvas.drawColor(Color.WHITE);//设置画布背景为白色 
//          canvas.drawRoundRect(300, 300, 600, 600, 150, 150, paint);//直接使用该行代码来画圆是行不通的，因为这个方法要求版本21，我的手机运行android版本是19 
          canvas.drawArc(rectF, -90, endAngle++, false, paint);//-90在这里不等于270，所以要想从最上方开始画弧，就得用-90 
          canvas.drawText(countTime(endAngle), pivotX, pivotX, paintText);//显示计算的时间 
          Thread.sleep(1000); 
        } catch (Exception e) { 
          e.printStackTrace(); 
        } finally { 
          if (canvas != null) {//需要对canvas进行非空判断 
            surfaceHolder.unlockCanvasAndPost(canvas); 
          } 
        } 
      } 
    } 

@Override 
public void surfaceCreated(SurfaceHolder holder) { 
  if (!countThread.isAlive()) {//如果线程不存在，则启动线程——>当应用挂起的时候Thread是存在的，如果不做这个判断，会报“Thread already started ”错误 
    countThread.start();//SurfaceView创建时开启线程 
  } 
}