参考博客
IOS高级开发～Runtime（一）
http://blog.csdn.net/lizhongfu2013/article/details/9496705
apple官方参考
Object-C Runtime Programming Guide
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008048
Objective-C总Runtime的那点事儿（一）消息机制
http://justsee.iteye.com/blog/2163777