Скачать или смотреть Resolving @ Published and @ ObservedObject Issues with SwiftUI Navigation Links

Discover how to effectively manage data between views in SwiftUI using `@ ObservedObject` and `@ Published`. Learn the best practices for achieving seamless navigation with navigation links.
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This video is based on the question https://stackoverflow.com/q/62733888/ asked by the user 'SD449' ( https://stackoverflow.com/u/11809796/ ) and on the answer https://stackoverflow.com/a/62738301/ provided by the user 'pawello2222' ( https://stackoverflow.com/u/8697793/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving @ Published and @ ObservedObject Issues with SwiftUI Navigation Links

Navigating between views in SwiftUI while managing state can sometimes feel like a complicated puzzle. One such issue arises when you're using @ Published properties in combination with @ ObservedObject and NavigationLink, particularly when attempting to pass data to a second screen. Today, we’ll look at a specific problem involving an ObservableObject and its interaction with NavigationLink, ensuring that updated values are reflected correctly across your views.

The Problem

Our scenario begins with a SwiftUI view that displays and modifies a number using a Picker. The number is tied to a Data class, which is an ObservableObject with a @ Published property. Although everything works smoothly on the first screen, once we navigate to the second screen using a NavigationLink, the updated number falls flat, displaying only the initial value plus one.

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With a NavigationLink set up to transition to the QuestionView, you might encounter this problem:

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In the QuestionView, you're attempting to display the updated number like so:

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The problem lies in the fact that the QuestionView is initializing a new instance of the Data class, leading it to always show the default initialized value (5) instead of the updated one from the previous view.

The Solution

Step 1: Pass the Data Object

Instead of creating a new instance of the Data class when navigating, we'll pass the existing instance to the QuestionView. This ensures that any updates made on the first screen are reflected when navigating to the second.

Here’s how you can modify your NavigationLink to pass the data object as a parameter:

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Step 2: Update QuestionView to Accept the Object

Now, we need to adjust the QuestionView to accept this Data instance. Here’s how you modify the QuestionView:

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Benefits of This Approach

Simplicity: This method requires minimal changes to your existing code.

Scalability: If you decide to include more properties from the Data class in QuestionView, it can be seamlessly done since you are already working with the same instance.

Reactivity: Changes made to data.number in the main view will automatically propagate to the QuestionView, ensuring the user sees the most up-to-date information.

Conclusion

Solving issues with SwiftUI's data flow is all about using the right tools effectively. By passing your ObservableObject as an @ ObservedObject into NavigationLink, you're not just fixing the immediate problem but also paving the way for a much more maintainable and scalable codebase.

If you encounter difficulties, remember that SwiftUI is designed to facilitate your interactions with the UI, allowing for efficient data management across views. With this approach, you can confidently build your applications while ensuring smooth navigation and accurate state management.