Resolving SwiftUI View Updates with ObservableObject and @ Published

Learn how to dynamically update your SwiftUI views based on ViewModel states by utilizing `ObservableObject` and `@ Published`.
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Updating SwiftUI View Based on ViewModel States

SwiftUI provides a modern way to build user interfaces across all Apple platforms. However, many users encounter challenges when transitioning from using @ State properties to the @ ObservedObject pattern in SwiftUI. An issue frequently faced is ensuring that the view correctly reflects changes in the underlying data managed by a ViewModel. In this post, we’ll explore how to implement updates to your SwiftUI view using the ObservableObject protocol and the @ Published property wrapper.

The Problem

As developers move their logic away from directly manipulating state within their views using @ State, they sometimes find that their views do not refresh as expected when properties in their ViewModel change. For instance, you might have a ViewModel structured like this:

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

In SwiftUI, you might want to update your view based on whether the data is loading, if there’s an error, or if there are movies to display. However, without additional steps, changing the properties in your ViewModel won't trigger a view update.

The Solution

Adding @ Published Properties

To ensure that your view reflects changes made to your ViewModel's state, you need to make use of the @ Published property wrapper. This allows SwiftUI to observe your properties for changes automatically. Here’s how to implement it in your ViewModel:

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

By adding @ Published before each property, you inform SwiftUI that any changes to these particular properties should trigger a view update.

Implementing the View

Here’s how you would structure the SwiftUI view to utilize this ViewModel correctly:

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

Here, the view responds dynamically to changes in contentViewModel. When isLoading changes, or if the movies array is updated or an error is set, the corresponding view updates will occur automatically.

Key Considerations

Make sure that your properties are marked as @ Published to notify SwiftUI of updates.

If you pass the ViewModel to child views, remember to use @ StateObject in the parent view and @ ObservedObject in the children. This ensures that the state of the ViewModel is maintained and propagated correctly throughout your view hierarchy.

Conclusion

Transitioning from @ State to using @ ObservedObject and @ Published can enhance the structure and maintainability of your SwiftUI applications. By ensuring your ViewModel properties are marked with @ Published, you can keep your UI in sync with your data model seamlessly. This not only makes your code cleaner but also enables a more reactive programming style that is at the heart of SwiftUI.

If you face issues with your views not updating, check that you’re leveraging these tools correctly! Happy coding!