WKWebView的scrollview的代理引起崩溃

记录工作遇到WKWebView的一个问题:

两个视图控制器:'AViewContrller','BViewContrller'

A有事件:
A -->push or present-->B,

B控制器的View添加了WKWebView的实例wkWebView,
并且设置了wkWebView.scrollView.delegate = self,
则当B返回A的时候会发生crash.

控制台提示:

Cannot form weak reference to instance (0x110c5dc0a) of class BViewContrller.
It is possible that this object was over-released,
or is in the process of deallocation.

在91®编程问答找到解决办法:

在BViewContrller的deinit里设置  
wkWebView.scrollView.delegate = nil