http://www.jianshu.com/p/0497afdad36d
http://www.jianshu.com/p/d96973e15e4a
http://www.cnblogs.com/wengzilin/p/4704996.html
http://www.vienta.me/2016/09/21/AOP%E5%9C%A8iOS%E4%B8%AD%E7%9A%84%E5%AE%9E%E8%B7%B5%E4%B8%80%E7%BB%9F%E8%AE%A1%E5%9F%8B%E7%82%B9/
