http://www.jianshu.com/p/169e31cacf42
http://www.jianshu.com/p/7f8472a97aa6
https://segmentfault.com/a/1190000004237771
App Extension
http://www.jianshu.com/p/aa1d5bf7cc47
http://www.cnblogs.com/xdream86/p/3855932.html
