ipad iphone　屏幕触摸事件编写
　新手在编写ipad和iphone的屏幕触摸事件的时候往往不知道如何处理。
其实只要再UIController里面重写一下方法即可：
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event;