Скачать или смотреть Understanding Why Your View Controller's Navigation Controller Property is nil After Being Pushed

Discover the reasons behind a view controller's navigation controller property being `nil` after it is pushed onto a navigation stack in Swift. Learn how to troubleshoot and resolve the issue effectively!
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This video is based on the question https://stackoverflow.com/q/76673685/ asked by the user 'fingia' ( https://stackoverflow.com/u/2332378/ ) and on the answer https://stackoverflow.com/a/76674198/ provided by the user 'DonMag' ( https://stackoverflow.com/u/6257435/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Why Your View Controller's Navigation Controller Property is nil After Being Pushed

When working with UIKit in Swift, developers sometimes face a perplexing problem: a view controller's navigation controller property turns out to be nil right after being pushed onto a navigation stack. This post will explain why this happens and how to fix it, ensuring your app's navigation works as intended.

The Problem: Navigation Controller Property is Nil

Imagine you are developing an iOS application using UIKit, and you set up your view controllers within a navigation controller. After pushing a new view controller onto the navigation stack, you might check the navigationController property of the newly pushed view controller, only to find that it returns nil. This situation can leave many developers scratching their heads, wondering what went wrong.

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Why is This Happening?

The key to understanding this issue lies in timing. When you push a new view controller onto a navigation stack with animation set to true, there is a delay before the transition completes. This can result in the following:

View Controller State: When you push a view controller, its navigationController property does not get updated immediately.

Asynchronous Nature: The push animation is processed asynchronously, meaning that the code executing right after the push call runs before the push transition is completed.

As a consequence, when you inspect vc2.navigationController immediately after the push, it can still return nil.

Solution: Change the Animation Parameter

To resolve this issue, you can change the animation parameter when pushing the view controller. By setting the animated parameter to false, the view controller gets immediately added to the stack without any transition delays. This way, the navigation controller property of the new view controller will be populated correctly right after the push.

Example Modifications

Here's how you can modify your code:

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Summary of Key Points

A view controller's navigationController property can be nil right after being pushed due to asynchronous transitions.

The animation delay interferes with the timing of the property update.

To fix this, consider disabling the animation when pushing view controllers in scenarios where you immediately need to interact with their properties.

Conclusion

Understanding why your new view controller's navigationController property can be nil after a push is essential for creating smooth navigation in your iOS applications. By recognizing the impact of animation timing, you can effectively troubleshoot this common issue and ensure that your app behaves as expected. Happy coding!