Скачать или смотреть Resolving Generic Property Issues in Swift Protocols with Associated Types

Learn how to effectively handle generics and associated types in Swift protocols and streamline your code for UITableView and UICollectionView implementations.
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This video is based on the question https://stackoverflow.com/q/63298118/ asked by the user 'Sandeep Bhandari' ( https://stackoverflow.com/u/5706328/ ) and on the answer https://stackoverflow.com/a/63301729/ provided by the user 'Rob C' ( https://stackoverflow.com/u/4081597/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Resolve Generic Property Issues in Swift Protocols with Associated Types

In iOS development, working with UITableView and UICollectionView can present challenges, especially when you want to share common logic between them while using generic types and associated types in protocols. One common issue developers encounter is regarding how to resolve generics when the views and view models must maintain specific relationships with each other, especially when using protocols. Let’s explore this problem and its solution in-depth.

The Problem

Imagine you have a base view model class, BaseCollectionsViewModel, which is generic and designed to work with UITableView and UICollectionView. In your code, you create a protocol BaseCollectionsViewProtocol with an associated type. The issue arises when you try to implement this protocol in your final class, and the compiler indicates that there's a problem with conformance.

Your original view model class and protocol looked like this:

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When you attempt to use the protocol in your view class, like so:

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The compiler will raise an error stating there's a conformance issue. The crux of the problem lies in the handling of generics and type invariance between your BaseCollectionsViewModel and the specific TrackingTableViewModel instance.

Solution Breakdown

To resolve this confusion and improve your design, consider changing the way you define your protocol and the view model relationship. Follow these steps:

Step 1: Define a ViewModel Protocol

Create a protocol for your view model that specifies the type of the data it will handle. This offers better encapsulation and clarity as it separates the data handling logic from the view logic.

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Step 2: Implement a Generic ViewModel Class

Utilize this protocol in your base view model class, maintaining generic behavior while adding clarity to its role.

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Step 3: Update the Base Collections View Protocol

Refactor the base protocol to define a type constraint directly on the view model, allowing greater flexibility.

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Step 4: Implement Final Classes

Finally, implement your actual table view model and table view class with the updated structures:

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Conclusion

By strategically employing associated types and protocols, you can effectively resolve the complications arising from generics in Swift. This approach allows you to maintain robust code, encourages code reuse, and ensures that UITableView and UICollectionView can share common implementations seamlessly. Experiment with these techniques in your own projects to streamline your code and eliminate confusion around generic types. Happy coding!