Understanding the Warning: Dismissing a View Controller from an Embedded Presented View Controller

When working with view controllers in iOS, it’s not uncommon to encounter warnings or errors related to dismissing view controllers. In this article, we’ll delve into one such warning that you may have encountered while trying to dismiss a UINavigationController embedded in another presented view controller.

Introduction to Presented View Controllers

In iOS, a presented view controller is a view controller that is shown on top of another view controller or the main window of an app. Presented view controllers can be used to create modal windows, popovers, and other types of overlays that provide additional functionality to the user.

When you present a view controller, it becomes the topmost view controller in the app’s navigation stack. This means that any view controller attempts to dismiss using dismiss(animated:completion:) will fail because the presented view controller is already at the top of the navigation stack.

The Warning: Dismissing a View Controller from an Embedded Presented View Controller

The warning you’re seeing is likely because you’re trying to dismiss the view controller that presents another view controller. In your case, ChecklistView presents ItemDetailView. When the user taps the “Cancel” button on ItemDetailView, it calls the delegate method itemDetailViewControllerDidCancel: which attempts to dismiss the presenting view controller (ChecklistView) using dismiss(animated:completion:).

However, because ChecklistView is already at the top of the navigation stack as a presented view controller, attempting to dismiss it from within itself will result in this warning.

Why You Shouldn’t Dismiss a View Controller Using the Delegate

The delegate method you’ve implemented for itemDetailViewControllerDidCancel: attempts to dismiss the presenting view controller using [self.delegate itemDetailViewControllerDidCancel:self]. However, this approach is not correct.

When you present one view controller from another, you’re creating a strong reference cycle between the two view controllers. This means that both view controllers are holding onto each other, and neither can be deallocated until the other is removed from the navigation stack.

By trying to dismiss the presenting view controller using the delegate, you’re introducing an additional layer of complexity into this cycle. You should instead use the presentingViewController property on the presented view controller to dismiss it.

Dismissing a View Controller Using the Presenting View Controller

To resolve the warning and avoid the issues with dismissed view controllers, you can modify your code to use the presentingViewController property. Here’s an example:

- (IBAction)cancel {
    [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
}

By using this approach, you’re breaking the strong reference cycle between the presented and presenting view controllers. The presenting view controller will be able to be deallocated once it’s removed from the navigation stack.

To understand why this is the case, let’s take a look at how the navigation stack works in iOS.

When you push a new view controller onto the navigation stack, it becomes the topmost view controller. Any subsequent pushes will add additional view controllers on top of the previous one.

However, when you present one view controller from another, you’re creating a presented view controller that sits on top of the existing view controller in the navigation stack. This presented view controller is not actually being pushed onto the navigation stack; it’s simply sitting on top of it.

This means that any attempt to dismiss the presenting view controller using dismiss(animated:completion:) will fail because it’s already at the top of the navigation stack.

Conclusion

In this article, we’ve explored a common warning related to dismissing view controllers from embedded presented view controllers. We’ve discussed why attempting to dismiss a view controller using its delegate is not recommended and instead showed how to use the presentingViewController property on the presented view controller to safely dismiss it.

By understanding how presented view controllers work and breaking the strong reference cycle between them, you can resolve this warning and ensure your app runs smoothly.

Last modified on 2024-02-13