Resolving View Redraw Issues in SwiftUI with @ StateObject

Discover how to address the bug where your SwiftUI view redraws unexpectedly and loses data by using `@ StateObject` instead of `@ ObservedObject`.
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Resolving View Redraw Issues in SwiftUI with @ StateObject

When developing applications with SwiftUI, it's common to encounter issues that can be quite perplexing. One such issue is when data from an ObservableObject fails to render properly in the view, sometimes even disappearing during a redraw. Let's delve into a real-world problem and explore a straightforward solution.

The Problem Breakdown

What Happened?

Imagine you are using Combine to connect to a REST API, retrieving data into an ObservableObject. In this scenario, the data is being observed in your SwiftUI view, utilizing the Model-View-ViewModel (MVVM) design pattern. However, you notice a frustrating bug: the view is drawn twice. Initially, it displays the data correctly, but upon re-drawing, the data vanishes.

Key Observations

View Redraws: The view appears to render twice, with the first draw showing data successfully and the second draw devoid of this data.

Single API Call: Your debugging confirms that the code fetching data is not executed a second time, suggesting that the issue lies within the view lifecycle rather than the data-fetching logic.

Rendered Text Views: The SwiftUI hierarchy hints that the Text views meant to display the fetched data are possibly deleted during the second rendering.

The Solution: Use @ StateObject

So, how can this issue be resolved? The answer lies in the use of different property wrappers to manage the lifecycle of your ObservableObject within the SwiftUI view.

Transitioning to @ StateObject

Instead of using @ ObservedObject for your ItemViewModel, you should switch to using @ StateObject. This change will ensure that the ItemViewModel retains its instance across view redraws, preventing the data from disappearing.

Here's the updated line of code you should implement in your view:

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

Why @ StateObject?

Preserving State: @ StateObject creates and stores an observable object in the view lifecycle. Unlike @ ObservedObject, which re-initializes the observable object each time the view is recreated, @ StateObject maintains the same instance.

Effect on Rendering: By using @ StateObject, your view can manage the observable state appropriately, ensuring that the pulled data persists and is available during view updates.

Example Update

Updating your TreatmentCardView would look like the following:

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

Conclusion

In SwiftUI, managing your observable objects appropriately is crucial for smooth functionality and user experience. Switching from @ ObservedObject to @ StateObject can significantly mitigate issues experienced during the view redraw process, ensuring that your data stays intact. If you're grappling with similar issues, implementing this change could streamline your views and enhance data handling in your SwiftUI applications.

By adopting this simple yet effective solution, you can enhance the reliability of your SwiftUI views. Happy coding!