Скачать или смотреть Troubleshooting SwiftUI: Fixing Result values in '? :' have mismatching types Error in List Styles

Discover how to solve the `Result values in '? :' have mismatching types` error in SwiftUI by implementing custom modifiers for List styles across different platforms.
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This video is based on the question https://stackoverflow.com/q/65267201/ asked by the user 'Alessio Rubicini' ( https://stackoverflow.com/u/8705504/ ) and on the answer https://stackoverflow.com/a/65267321/ provided by the user 'Asperi' ( https://stackoverflow.com/u/12299030/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting SwiftUI: Fixing the Result values in '? :' have mismatching types Error in List Styles

When developing a SwiftUI application that runs on both iOS and macOS, you might encounter some unexpected issues, especially when attempting to utilize different List styles. One common error is the message about mismatching types when using the conditional operator ? :. This error indicates that the Swift type checker cannot reconcile the two types you're trying to combine into a single List style. Let's delve into this issue and find out how to solve it effectively.

Understanding the Problem

In your SwiftUI code, you attempt to switch between InsetGroupedListStyle() for iOS and DefaultListStyle() for macOS, like this:

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

However, when the Swift compiler processes this line, it throws an error because InsetGroupedListStyle and DefaultListStyle are different data types. As they cannot be reconciled by the type system, you receive the error message:

Result values in '? :' expression have mismatching types 'InsetGroupedListStyle' and 'DefaultListStyle'.

While both are indeed List styles, they belong to different types, hence the discrepancy.

The Solution: Custom Modifier

To overcome this error, you can create a custom modifier for your List. This approach allows you to handle the List styles conditionally without the need for a confusing type mismatch. Below are the steps to implement the solution effectively.

Step 1: Creating the Inset Style Modifier

You can extend the List view in SwiftUI by creating a custom function, insetListStyle. This function will apply the InsetGroupedListStyle based on a boolean flag. Here's how you can do that:

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

Step 2: Using the Custom Modifier

Now that you have defined the custom modifier, you can utilize it within your List in the following manner:

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

Benefits of This Approach

Type Safety: By using a custom modifier, you eliminate the type mismatch issue, ensuring that the Swift compiler correctly interprets the List's styles.

Code Clarity: The custom modifier approach simplifies your view-building logic, making it cleaner and easier to read.

Flexibility: This method provides you with the adaptability to add more conditions in the future if necessary.

Conclusion

Handling platform-specific dependencies in SwiftUI can be challenging, especially when different styles and features apply to various environments. However, by utilizing a custom modifier for List styles, you can effectively resolve the type mismatch issue that arises when switching between iOS and macOS.

Next time you run into the Result values in '? :' have mismatching types error, remember that creating a tailored modifier can facilitate a clean and efficient solution. Happy coding!