ios - swizzle popViewControllerAnimated 时的 EXC_BAD_ACCESS：

Question

为了记录控制器之间的导航，我使用了 -popViewControllersAnimated: 方法的 swizzling。有时它会导致 EXC_BAD_ACCESS 出现奇怪的崩溃。可能是什么原因？

- (void)sw_popViewControllerAnimated:(BOOL)animated {

//1. get top controller before pop
//2. pop
//3. get top controller after pop
//4. log it
NSString *controllerFromIdentifier = @"";
__block NSString *controllerToIdentifier = @"";

    NSDictionary *controllerFromAdditionalParams = @{};

    UIViewController *topController = ((UINavigationController*)self).topViewController;

    [self sw_popViewControllerAnimated:animated];

    UIViewController *topControllerAfterPop = ((UINavigationController*)self).topViewController;

}