iOS12

ios 12 中的新特性。 已經有很多文章寫得很好，這里不再贅述，直接給大家幾個傳送門：

https://sspai.com/post/47168

https://post.smzdm.com/p/771705/

https://www.jianshu.com/p/dde4fef41c4b

https://www.jianshu.com/p/8b49fc037a89

http://www.cocoachina.com/ios/20180926/25026.html

https://baijiahao.baidu.com/s?id=1611958169330021624&wfr=spider&for=pc

https://www.jianshu.com/p/b93753843a67