1、show functoins
https://www.iteblog.com/archives/2032.html?from=related
https://blog.csdn.net/u013980127/article/details/52606024
http://www.cnblogs.com/felix-xwz/p/4455117.html
https://blog.csdn.net/abc50319/article/details/80452368
https://blog.csdn.net/liuzhoulong/article/details/77969224