isBeingDismissed not set in viewWillDisappear:

问题

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?

回答1:

Your issue is how you are dismissing your modal view. How is rootViewController being defined?

When I call [self dismissModalViewControllerAnimated:YES] then [self isBeingDismissed] evaluates to true.

When I call [parentViewController dismissModalViewControllerAnimated:YES] then [self isBeingDismissed] evaluates to true, whereby parentViewController is the UIViewController that presented the modal view (note: not a UINavigationController).

回答2:

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.

回答3:

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.isMovingFromParentViewController ||          
               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.

回答4:

If by some chance you came here trying to use isBeingDismissed on a non-modally presented view controller, you can always check the topViewController property of your navigationController, for instance:

if navigationController?.topViewController != self {
    return
}

回答5:

        viewController.isBeingPresented == NO;
        [rootVC presentViewController:viewController animated:NO completion:^{
            viewController.isBeingPresented == NO;
            viewController.isBeingDismissed == NO;
            [viewController dismissViewControllerAnimated:NO completion:^{
                viewController.isBeingDismissed == NO;
            }];
            viewController.isBeingDismissed == NO;    // is not work
        }];
        viewController.isBeingPresented == YES;     // is work

        viewController.isBeingPresented == NO;
        [rootVC presentViewController:viewController animated:NO completion:^{
            viewController.isBeingPresented == NO;
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                viewController.isBeingDismissed == NO;
                [viewController dismissViewControllerAnimated:NO completion:^{
                    viewController.isBeingDismissed == NO;
                }];
                viewController.isBeingDismissed == YES;    // is work
            });
        }];
        viewController.isBeingPresented == YES;     // is work

来源：https://stackoverflow.com/questions/10248412/isbeingdismissed-not-set-in-viewwilldisappear

标签

iphone

ios

uiviewcontroller

modalviewcontroller