Скачать или смотреть Mastering List Binding in Swift 5.5

Discover how to effectively use the new binding feature in `List` with Swift 5.5 to ensure seamless interaction with your SwiftUI applications.
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This video is based on the question https://stackoverflow.com/q/68591407/ asked by the user 'Thomas' ( https://stackoverflow.com/u/15225776/ ) and on the answer https://stackoverflow.com/a/68592005/ provided by the user 'Joakim Danielson' ( https://stackoverflow.com/u/9223839/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering List Binding in Swift 5.5: A Simple Guide

In the realm of SwiftUI development, managing data efficiently is crucial, especially when it comes to building dynamic interfaces with lists. As of Swift 5.5, a new feature allows developers to create direct bindings to items in a List. While this sounds promising, many newcomers struggle with implementing it effectively. Let’s take a closer look at how to utilize these bindings in List correctly, focusing on a common challenge developers face when using this feature.

The Problem: Losing Focus on TextField

Imagine setting up a simple list populated with strings using TextField for editing. You click on an item to edit it, but immediately after typing just one character, the TextField loses focus. Frustrating, right? This is a common issue encountered by developers working with lists in SwiftUI.

Here’s a basic example of the code that may trigger this behavior:

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Let’s break down why this happens and how to fix it.

The Solution: Using an Identifiable Struct

The crux of the problem lies in how SwiftUI identifies and tracks these items in the list. When we use .self, each string in the array is treated as a unique identity. Thus, when we modify one of these strings via the TextField, SwiftUI perceives it as a deletion of the old item and insertion of a new one. As a result, the focus on the TextField is lost when the list updates, disrupting the user interaction.

Step 1: Create an Identifiable Struct

To resolve this issue, we can create a struct that conforms to the Identifiable protocol. This way, when you edit an item, SwiftUI can keep track of the changes based on a specified id. Here’s how you can structure your code:

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Step 2: Update the ContentView

Next, we’ll update our ContentView to utilize the new structure and binding method:

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Why This Works

By ensuring that our items have a unique identifier, SwiftUI can effectively manage state updates. This prevents the list from treating item changes as deletions and insertions, thereby preserving focus on the TextField during edits.

Important Notes

This behavior is expected and not a bug related to SwiftUI 3.0 or any beta version; it’s part of how SwiftUI detects changes.

When using custom objects with identifiable strings, always ensure they have a unique id. This practice leads to better performance and user experience in your applications.

Conclusion

By following the approach mentioned above, you can leverage SwiftUI's List feature in a robust manner, enabling clean and efficient data binding. The key takeaway is to use identifiable structs rather than strings or simple types when dealing with lists. This practice will save you from the typical pitfalls associated with focus loss in TextFields. Now, you can focus on building engaging SwiftUI applications with confidence!