isBeingDismissed not set in viewWillDisappear:

Question

I have some code to clean up in my viewWillDisappear:, which I only want to use when the view is moving back to the parent view controller.

- (void)viewWillDisappear:(BOOL)animated
{
    if ([self isMovingFromParentViewController] || [self isBeingDismissed]) {
        NSLog(@"isMovingFromParentViewController or isBeingDismissed");
        // clean up
    }
    [super viewWillDisappear:animated];
}

The view can be presented in two ways: it can be pushed by a navigation controller, or presented as a modal view controller (from the same navigation controller). If it's pushed, then popped (pressing the back button), my clean-up code runs. If it it presented as a modal view controller, then dismissed, the code doesn't run.

I dismiss like so:

[rootViewController dismissModalViewControllerAnimated:YES];

My question is: why isn't isBeingDismissed set when I dismiss my view controller?

Answer 1

If this is the first view controller in a modal navigation controller that's being dismissed, calling self.isBeingDimissed() from viewWillDisappear: returns false.

However, since the entire navigation controller is being dismissed, what actually works is self.navigationController?.isBeingDismissed(), which returns true.

Answer 2

As @Yuval Tal mentioned, this flag does not work when you're dismissing controller that is embeded inside navigation controller. Here's an extension that I use:

extension UIViewController 
{
    var isAboutToClose: Bool {
        return self.isBeingDismissed ||      
               self.isMovingFromParent ||          
               self.navigationController?.isBeingDismissed ?? false
    }
}

It can be easily extended when you find another case when standard .isBeingDismissed won't work. And if you find, let us, let me know in comments.