Solving the Inconsistent Icon Toggling in SwiftUI's LazyVGrid and LazyVStack

Discover how to resolve the confusing issue of inconsistent icon toggling in SwiftUI's LazyVGrid and LazyVStack with this comprehensive guide.
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This video is based on the question https://stackoverflow.com/q/63806871/ asked by the user 'Svenson' ( https://stackoverflow.com/u/1575217/ ) and on the answer https://stackoverflow.com/a/63824849/ provided by the user 'Svenson' ( https://stackoverflow.com/u/1575217/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Inconsistent Icon Toggling in SwiftUI's LazyVGrid and LazyVStack

When developing a SwiftUI application, you might encounter some unexpected behaviors, especially when working with LazyVGrid or LazyVStack. One common issue is the inconsistent toggling of icons, particularly in buttons that change their state based on user actions. In this post, we'll explore a specific problem where the heart icon used for a "favorites" functionality doesn't update as expected and discuss how to fix it.

The Problem: Inconsistent Icon Toggling

Imagine you're building a video game application where each game is represented as a card in a LazyVGrid. Each card has a button featuring a heart icon to mark games as favorites. While the functionality to add or remove games from the favorites list behaves correctly, the heart icon sometimes fails to update when you scroll through the list. This inconsistency can lead to a confusing user experience.

Symptoms

Heart icon does not toggle from filled to empty or vice versa after scrolling and pressing the button.

Actions tied to the button (adding/removing from favorites) are confirmed through print statements, but visual representation (the heart icon) remains static.

Investigation

The initial investigation led to a hypothesis that the problem lies within the LazyVGrid or LazyVStack. These views load items lazily for efficient rendering, which can sometimes affect the way states are observed and updated.

Key Terminology

LazyVGrid: A SwiftUI view that arranges its contents in a grid, rendering items only when they are about to be displayed.

@ ObservedObject: A property wrapper in SwiftUI that subscribes to an observable object and invalidates its view when the object changes.

The Solution: Updating View State Correctly

After reviewing the code for the favorites functionality, it was discovered that the update mechanism for the view state wasn't optimal. Here’s how to resolve the issue effectively:

Step 1: Correct the Order of Updates

In the Favorites class where the add and remove functions are located, the order of operations for updating the state was problematic. The objectWillChange.send() was called before the actual addition or removal of the game ID. This means the view could re-render before the data actually changed.

Updated Functions:

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

Step 2: Why LazyVGrid Was the Culprit

The reason you noticed this issue only when using LazyVGrid or LazyVStack is due to how these views handle rendering and state changes. When you scroll, and items are rendered, the views are instantiating and drawing based on the model's current state. If the state changes before the view has properly registered it, you can end up with an outdated representation.

In contrast, a VStack doesn't employ lazy loading, so it draws all its children at once. This leads to fewer chances for state and visual discrepancies.

Conclusion

By fixing the order of state updates in the Favorites class, you can resolve the inconsistent icon toggling in your LazyVGrid or LazyVStack. Ensuring your view state accurately reflects your model state is crucial, especially in UI designs where visual representation plays a critical role in user experience.

Final Thoughts

This experience highlights the importance of understanding data binding and state management in SwiftUI. As you continue to build applications, keeping these principles in mind will help you create smooth and reliable user interfaces.

Implement these changes and see how your app behaves differently — you might find that even small adjustments lead to a more polished and responsive application. Happy coding!