原理:
http://www.cnblogs.com/Fndroid/p/5354644.html
http://www.jianshu.com/p/28edf5352b63
开源库:
ButterKnife
https://zhuanlan.zhihu.com/p/21628698
https://zhuanlan.zhihu.com/p/20201755?columnSlug=fyales