How to Re-render UI in SwiftUI with Combine using Computed Properties

Learn how to effectively use Combine in SwiftUI to update your User Interface in response to changes in computed properties, making your applications more reactive and intuitive.
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How to Re-render UI in SwiftUI with Combine using Computed Properties

In the realm of reactive programming with SwiftUI and Combine, one common challenge is ensuring your User Interface (UI) updates in response to changes in the underlying data model. This is particularly relevant when dealing with computed properties that are nested within classes. If you've ever asked yourself, "How do I re-render the UI in response to a computed property buried in a nested class?"—you’re in the right place. In this post, we’ll explore a practical example of how to achieve just that.

Understanding the Problem

When using SwiftUI, your UI should reflect changes in your data model automatically. However, if your state is deep within nested classes, such as in the ViewModel structure, it may not be clear how to trigger updates in the UI. Specifically, you might have a computed property like this:

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

Your goal is to make the UI responsive to changes detected in this property. In our example, we will examine how to use Combine, Apple's reactive programming framework, to rebuild your view when the state changes.

The Solution Breakdown

Step 1: Introduce a Publisher

The key to making your UI reactive lies in creating a publisher that emits events when the state changes. We’ll start with a textPublisher, which sends changes to the person's name as it is updated:

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

Step 2: Create a Publisher for isComplete

Next, we will transform our publisher to indicate when the name is complete. This can be done by chaining operations to the textPublisher:

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

Step 3: Subscribing to Changes

Finally, you need a subscriber that responds to these changes. You can use a Subscriber to listen for changes emitted by the isComplete publisher. This allows you to perform any UI updates required when the state changes:

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

Conclusion

By employing Combine and creating a reactive pipeline, you can effectively manage UI updates in response to changes in computed properties under nested structures. This transition to thinking about model UI, rather than model UI, is crucial in developing modern, reactive applications with SwiftUI. Start integrating these patterns into your projects, and you’ll see your applications become more intuitive and responsive as user input changes.
By following the steps outlined in this post, you'll be well on your way to mastering UI reactivity in SwiftUI through Combine, leveraging computed properties and nested classes effectively.

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