事件注册
•1.通过编辑器绑定方法
•2.AddListener
•3.实现接口
•4.自定义框架
鼠标指针类
•IPointerEnterHandler
•IPointerExitHandler
•IPointerDownHandler
•IPointerUpHandler
•PointerClickHandler
拖拽类
•IBeginDragHandler
•IDragHandler
•IEndDragHandler
•IDropHandler
点选类
•IUpdateSelectedHandler
•ISelectHandler
•IDeselectHandler
输入类
•IScrollHandler
•IMoveHandler
•ISubmitHandler
•ICancelHandler