生命周期

https://blog.csdn.net/fengsh998/article/details/9039629

https://www.jianshu.com/p/61dff0c46ada

https://www.jianshu.com/p/d60b388b19f5

http://www.cnblogs.com/junhuawang/p/5742535.html

http://blog.sina.com.cn/s/blog_5da93c8f0102wkz9.html

https://bestswifter.com/uiviewlifetime/

https://www.jianshu.com/p/bca0acd690dd

https://www.jianshu.com/p/fcfbd4919b0b