Swift：应用程序在segue期间崩溃

Question

I have 3 view controllers that I'm navigating between. When I open my app, I start at Controller1, which I can then use to navigate to Controller2 or Controller3. I can navigate to each of them fine individually, however, after I go to Controller3, return to Controller1, then try to navigate to Controller2, I get an EXC_BAD_ACCESS with code = 1. There is no exception or error message given at all, it just takes me to my AppDelegate file and gives me that error code.

I don't know what the issue is, but something that seems relevant is that I'm setting Controller3 as the navigation controller's delegate. I have a fourth navigation controller that also is set as a delegate as well, and causes the same behavior when I from 1->4->1->2, just like with 1->3->1->2. I have no issue going from 1->4->1->3 or 1->3->1->4, only when 2 is involved. I'm not sure if the issue is the delegates, and the fact that 2 isn't being set as one. Once again, I can navigate to it fine by itself, but not after navigating to one of the other 2 sub-view controllers.

Answer 1

如果将Controller3或Controller4设置为导航控制器委托，则需要在这些类的viewWillDisappear函数中将其清除，否则最终将得到无效的引用，这就是导致崩溃的原因

Answer 2

I ran into this same kind of crash, so I will share what the issue was for me:

1. I had created a subclass of UIWebView.
2. In my storyboard, I dragged a UIWebView onto the canvas and changed it's class to be my subclass.

That was all working. The app had already passed through our QA team, was "accepted" by the business owner, and we were ready to push it to the app store.

Then I was told, "You can't use UIWebView. You must use WKWebView."

Fine, I changed my subclass to inherit from WKWebView, tweaked my internal class logic, and....splat. Trying to segue to that view controller would crash just as noted by the OP.

The problem was my storyboard: Because it was trying to instantiate my subclass, it was basically attempting to create a WKWebView which is NOT necessarily supported in Interface Builder (my friend says it might be ok in later versions, but I didn't verify).

TL;DR

The moral of the story is that if you have a subclassed object on your story board whose ancestor can't be dragged from the toolbox, then you will probably crash when you segue.