unity渲染层级关系小结
http://blog.csdn.net/meegomeego/article/details/42060389
NGUI研究院之三种方式监听NGUI的事件方法（七）
http://www.xuanyusong.com/archives/2390
Unity游戏界面解决方案: PSD For UGUI
http://mp.weixin.qq.com/s?__biz=MzI3MzA2MzE5Nw==&mid=2668903445&idx=1&sn=629fe719ddce0919aae7d56326e04a3f&scene=21#wechat_redirect