1.Image配合Canvas,可以修改层级。
2.CanvasGroup不能独立接收UI事件,需要Image和它的RaycastTarget打开。然后CanvasGroup需要BlocksRaycast打开。
3.子Canvas会阻碍UI事件
Unity UI Events not working for Canvas objects - Questions & Answers - Unity Discussions
4.transform.SetSiblingIndex
How do I change the sorting layer of a UI image when it is being dragged? - Questions & Answers - Unity Discussions
这个是排序卡牌用的关键所在