Скачать или смотреть Change View Controller from a Background Thread in Swift

Learn how to properly switch your View Controller from a background thread in Swift without causing fatal errors. This guide explains the solution step-by-step for better understanding.
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This video is based on the question https://stackoverflow.com/q/62868006/ asked by the user 'August Kimo' ( https://stackoverflow.com/u/13714686/ ) and on the answer https://stackoverflow.com/a/62868140/ provided by the user 'ryandu' ( https://stackoverflow.com/u/13770657/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Change View Controller from a Background Thread in Swift: A Simple Guide

When building custom iOS applications, especially with features like a camera, dealing with threads can become quite a tricky endeavor. One common issue developers encounter is switching View Controllers from a background thread, which can lead to fatal errors if not handled properly. If you've found yourself in this situation, you're in the right place! In this post, we'll break down the problem and provide a clear solution.

The Problem

In the process of developing a custom camera app, a developer faced a challenge: executing cleaning operations within a loop on a background thread while needing to navigate back to the main View Controller once that loop finished. The following key issues arose:

The background thread was managing a loop with a delay to take multiple pictures without interrupting an AVCaptureSession running on the main thread.

An attempt to call goBackHome() to switch the app's View Controller resulted in a fatal error stating that this operation can only be performed on the main thread.

Understanding this common roadblock is crucial for developers who wish to leverage background processing without compromising user interface changes.

The Solution

The good news is that this issue can be resolved relatively easily by ensuring that any UI updates, including changing View Controllers, are executed on the main thread. Here's how to do that with a step-by-step approach.

Step 1: Modify Your goBackHome() Function

Instead of directly calling goBackHome() in your background thread, you should wrap its contents in a DispatchQueue.main.async closure. By doing this, you effectively tell Swift to make the call on the main thread, avoiding the fatal error. Here’s how your updated function will look:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Calling goBackHome() in the Background Thread

Now that goBackHome() takes care of executing on the main thread, your loop in the background thread will still remain as is, except for the call to goBackHome(). Here’s how your takeAllPictures() function will look with this integration:

[[See Video to Reveal this Text or Code Snippet]]

Why This Works

The reason behind this method is simple: UI updates should always be on the main thread to ensure they can access and modify UI elements safely. By encapsulating your UI changes within DispatchQueue.main.async, you ensure that the transition back to the home ViewController is executed smoothly and without errors.

Conclusion

Switching View Controllers from a background thread in Swift may seem like a daunting task, but with the right approach, it becomes manageable. By utilizing DispatchQueue.main.async, you ensure that UI changes are executed on the appropriate thread, preventing fatal errors and enhancing user experience.

By following these guidelines, you can build robust applications that effectively utilize background processes while maintaining a responsive interface. Happy coding!