Crash happened when UINavigationController doing transaction - ios

Question

I just got a crash showing as the following screen shot, it happened when I click the back button on the navigation bar, is any typical situation will cause this crash?

Answer 1

In my experience there was an issue introduced in iOS 7 making it possible for you to start a transition before another has ended, which ultimately causes this crash. You can reproduce this manually if you put 2 navigation calls back to back and run them, such as:
[self.navigationController pushViewController:whatever animated:YES];
[self.navigationController pushViewController:whatever2 animated:YES];
If you do this, you will eventually see that crash occur.
The easiest way I found to make sure this never happens is by subclassing UINavigationController and implementing the UINavigationControllerDelegate to prevent overlapping transitions.
Once I began using the code below, the number of crashes I see due to this issue has dropped to 0.
One thing to note is that if you actually need to implement another <UINavigationControllerDelegate> you will need to write some code to store the extra delegate yourself and pass on the delegate calls, perhaps using NSProxy or something like that.
#interface MyNavigationController () <UINavigationControllerDelegate>
{
// used to prevent "can't add self as subview" crashes which occur when trying to animate 2 transitions simultaneously
BOOL _currentlyAnimating;
}
#end
#implementation MyNavigationController
- (void) viewDidLoad
{
[super viewDidLoad];
self.delegate = self;
}
- (void) pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
if(_currentlyAnimating)
{
return;
}
else if(animated)
{
_currentlyAnimating = YES;
}
[super pushViewController:viewController animated:animated];
}
- (UIViewController *) popViewControllerAnimated:(BOOL)animated
{
if(_currentlyAnimating)
{
return nil;
}
else if(animated)
{
_currentlyAnimating = YES;
}
return [super popViewControllerAnimated:animated];
}
- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
_currentlyAnimating = NO;
}
- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
// tracking cancelled interactive pop
// http://stackoverflow.com/questions/23484310/canceling-interactive-uinavigationcontroller-pop-gesture-does-not-call-uinavigat
[[self transitionCoordinator] notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext> context)
{
if([context isCancelled])
{
UIViewController *fromViewController = [context viewControllerForKey:UITransitionContextFromViewControllerKey];
[self navigationController:navigationController willShowViewController:fromViewController animated:animated];
if([self respondsToSelector:#selector(navigationController:didShowViewController:animated:)])
{
NSTimeInterval animationCompletion = [context transitionDuration] * [context percentComplete];
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (uint64_t)animationCompletion * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
[self navigationController:navigationController didShowViewController:fromViewController animated:animated];
});
}
}
}];
}
#end