重写SurfaceView 的 onTouchEvent实现拖动

public boolean onTouchEvent(MotionEvent event) {
	float npx = event.getX();
	float npy = event.getY();
	switch(event.getAction())
	{
	case MotionEvent.ACTION_DOWN:
		Rect r = new Rect((int) (x-1), (int) (y-1)
				, (int) (x+strWidth+2), (int) (y+ 20));
		if(r.contains((int)npx, (int)npy))
		{
			//人为控制物体
			isControlByFigner = true;
			offFignerX = npx - x + 1;
			offFignerY = npy - y + 1;
		}
		break;
	case MotionEvent.ACTION_MOVE:
		if(isControlByFigner)
		{
		//跟随手指
		x = npx - offFignerX +1;
		y = npx - offFignerY +1;
		//计算时差
		timeOffset = System.currentTimeMillis() - timeRecord;
		timeRecord = System.currentTimeMillis();
		}
		break;
	case MotionEvent.ACTION_UP:
		if(isControlByFigner)
		{
			//计算释放时的速度
			Vx = (npx - opx)/timeOffset;
			Vx = (npy - opy)/timeOffset;
			//释放手指
			isControlByFigner = false;
		}
		break;
	}
	opx = npy;
	opy = npy;
	this.invalidate();
	return super.onTouchEvent(event);
}