http://www.cnblogs.com/yingzhongwen/p/4568350.html 讲了委托与事件，但是对异步委托研究得还不够深入。

http://www.cnblogs.com/lxblog/archive/2012/12/11/2813893.html

http://www.cnblogs.com/IAmBetter/archive/2012/02/13/2348912.html

http://blog.csdn.net/lexiaoyao20/article/details/6917295