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Learn how to effectively implement `@ObservedObject` in SwiftUI using a well-structured MVVM approach to ensure your views update automatically upon data changes.
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This video is based on the question https://stackoverflow.com/q/74171322/ asked by the user 'Jonas Bäumer' ( https://stackoverflow.com/u/16929076/ ) and on the answer https://stackoverflow.com/a/74172253/ provided by the user 'Pastre' ( https://stackoverflow.com/u/6178714/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Triggering Automatic SwiftUI Updates with @ObservedObject in MVVM

If you're developing an iOS application using SwiftUI and are looking to implement the MVVM (Model-View-ViewModel) architecture, you may encounter some challenges when trying to make your UI responsive to data changes. A common problem arises when a UI component fails to update automatically after an event, such as a button press. In this post, we’ll explore how to properly trigger automatic updates in SwiftUI using the @ObservedObject and @StateObject properties, ensuring your app behaves as expected.

The Challenge: UI Not Updating

Imagine you have a SwiftUI view where you want to display a number that increments each time a button is pressed, but the UI doesn’t update correctly when using a ViewModel. This problem typically occurs when the data handling does not adhere strictly to the MVVM design pattern. The following was the initial approach taken:

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While this code may seem functional at a glance, it ultimately fails to deliver the expected behavior when it comes to automatically updating the UI after the button press.

A Better Solution: Organizing Code Within MVVM

To solve this issue, it’s essential to refine the structure of your SwiftUI code to better align with MVVM principles. Essentially, your ViewModel needs to manage the state of your model instead of exposing the model directly to the view. Here’s how to organize your code effectively:

1. Update the View

Instead of using an @ObservedObject directly for your model in the view, you should instantiate your view model as a @StateObject which will manage the number state appropriately:

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2. Revise the ViewModel

Next, your ViewModel should encapsulate your model and expose a simple @Published property for the view:

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3. Model Implementation

Finally, the NumberStorage model should handle the logic of number incrementation and notify the ViewModel about state changes:

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

Key Takeaways

By structuring your SwiftUI application following these guidelines, you can ensure that your UI responds dynamically to data changes, utilizing the powerful features of Combine with @Published properties. Here's a summary of the most important points:

Use @StateObject in your view for a ViewModel that needs to handle state.

Ensure your ViewModel encapsulates all data logic and exposes only what's necessary to the view.

Bind model updates using Combine to keep your view responsive and up-to-date.

This approach leads to cleaner, more maintainable code and a smoothly functioning UI in your SwiftUI applications.

If you have any questions or need further clarification on implementing MVVM with SwiftUI, feel free to reach out!