Скачать или смотреть Resolving SwiftUI Preview Crashes with @ available Attributes in Xcode

Discover how to fix SwiftUI Preview crashes in Xcode when extending Views with proper `@ available` attributes to ensure compatibility with iOS 13 and above.
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This video is based on the question https://stackoverflow.com/q/62313443/ asked by the user 'Michael Berk' ( https://stackoverflow.com/u/11704346/ ) and on the answer https://stackoverflow.com/a/62313478/ provided by the user 'Muhand Jumah' ( https://stackoverflow.com/u/7255875/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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SwiftUI Preview Crashes: Solving the @ available Dilemma

If you're developing a SwiftUI project that needs to support iOS versions older than 13, you might have encountered an annoying problem: your SwiftUI Preview crashes in Xcode, especially when you extend the View. This issue is not only frustrating, but it can also significantly hinder your workflow. In this guide, we’ll dive into the details of what causes this crash and how you can effectively resolve it.

The Problem: Understanding the Crash

What Happens?

When extending a SwiftUI struct like View, you might see the following error message in your SwiftUI Preview:

Failed to build myView.swift

'View' is only available in iOS 13.0 or newer

Action: add @ available attribute to enclosing extension

Despite adding the @ available(iOS 13.0, *) attribute to your extension, you're still facing crashes when you add any functionality beyond a blank extension. So, what’s going on beneath the surface?

Key Observations

The Preview works fine with an empty extension but crashes as soon as you introduce a function or static property.

Attempting to reboot, add multiple @ available attributes, or cleaning the DerivedData folder has no effect on the crash.

The Solution: Fixing the Crash

The red flag here is understanding how SwiftUI interacts with availability attributes, especially for lower iOS versions. Here’s how you can resolve the issue step by step.

Step 1: Remove Redundant @ available Attribute

It turns out you do not need the @ available(iOS 13.0, *) in the extension, as your app will not run on devices below iOS 13. The presence of this attribute is redundant and could cause complications with the Preview. Removing it can often fix the issue.

Step 2: Check for Weak Linking

If you are employing weak linking for SwiftUI, follow the steps below to ensure everything is set up correctly:

Set SwiftUI.framework to Optional:

Go to Build Phases.

Look for Link Binary With Libraries.

Ensure that SwiftUI.framework is set to Optional.

Step 3: Correct Placement of @ available Attribute

If weak linking is indeed necessary, make sure to place the @ available(iOS 13.0, *) attribute correctly. It should be on top of your body property, not on top of your extension.

Here is an example of how your code should look:

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

With this setup, your Preview should now function correctly without crashing.

Conclusion: Best Practices for SwiftUI Development

When working with SwiftUI and targeting different iOS versions, always ensure you:

Remove unnecessary @ available attributes in extensions.

Confirm that weak linking is correctly configured.

Carefully position your availability attributes for properties and functions.

Following these guidelines will not only help you avoid crashing previews but also enhance your development experience. Happy coding!