https://stackoverflow.com/questions/36280699/how-to-set-a-custom-views-intrinsic-content-size-in-swift
Autolayout的布局， 监听这两个 NSNotification.Name.UIKeyboardWillShow, NSNotification.Name.UIKeyboardWillHide 通知的方法里
invalidateIntrinsicContentSize后再调用layoutIfNeeded 会引起动画