使用EventTrigger添加OnPointerXXX回调事件

使用OnPointerXXX有两种方式，一种是实现IPointerXXXHandler接口，另一种就是利用EventTrigger添加回调事件。如下：

EventTrigger trigger = compareBtn.GetComponent<EventTrigger>();

        EventTrigger.Entry entry = new EventTrigger.Entry();

        entry.eventID = EventTriggerType.PointerDown;

        entry.callback.AddListener((data) =>

        {

            OnPointerDownDelegate((PointerEventData)data);

        });

        trigger.triggers.Add(entry);

        EventTrigger.Entry entry2 = new EventTrigger.Entry();

        entry2.eventID = EventTriggerType.PointerUp;

        entry2.callback.AddListener((data) =>

        {

            OnPointerUpDelegate((PointerEventData)data);

        });

        trigger.triggers.Add(entry2);