触摸事件touchBegin 等一系列方法
1）手指按下
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
2）按下并移动
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;
3）手指松开
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;
4）非正常取消，也就是意外中断
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event;
