Unity UI组件实现所用到的接口类（如果UGUI的组件达不到需求的效果可以依此自己实现）

全部是接口，需要引用UnityEngine.EventSystems命名空间

17个接口事件；继承接口，并实现其中的方法即可
IPointerEnterHandler – OnPointerEnter – Called when a pointer enters the object
（鼠标悬停在UI物体的时候会触发）

IPointerExitHandler – OnPointerExit – Called when a pointer exits the object
（鼠标离开UI物体的时候会触发）

IPointerDownHandler – OnPointerDown – Called when a pointer is pressed on the object
（鼠标点击按下的那一帧）

IPointerUpHandler – OnPointerUp – Called when a pointer is released (called on the original the pressed object)
（鼠标点击抬起的那一帧）

IPointerClickHandler – OnPointerClick – Called when a pointer is pressed and released on the same object
（鼠标点击一次的那段时间一直调用）

IBeginDragHandler – OnBeginDrag – Called on the drag object when dragging is about to begin
（开始拖拽的那一帧）

IDragHandler – OnDrag – Called on the drag object when a drag is happening
（拖拽过程当中）

IEndDragHandler – OnEndDrag – Called on the drag object when a drag finishes
（结束拖拽过程的那一帧）

IDropHandler – OnDrop – Called on the object where a drag finishes
IScrollHandler – OnScroll – Called when a mouse wheel scrolls
IUpdateSelectedHandler – OnUpdateSelected – Called on the selected object each tick
ISelectHandler – OnSelect – Called when the object becomes the selected object
IDeselectHandler – OnDeselect – Called on the selected object becomes deselected
IMoveHandler – OnMove – Called when a move event occurs (left, right, up, down, ect)
ISubmitHandler – OnSubmit – Called when the submit button is pressed
ICancelHandler – OnCancel – Called when the cancel button is pressed