Скачать или смотреть How to Correctly Handle @ EnvironmentObject in SwiftUI with Secondary Classes

Learn how to effectively use `@ EnvironmentObject` within secondary classes in SwiftUI, resolving common crashes and ensuring proper state management.
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This video is based on the question https://stackoverflow.com/q/63368098/ asked by the user 'Michael Rowe' ( https://stackoverflow.com/u/373749/ ) and on the answer https://stackoverflow.com/a/63368236/ provided by the user 'achu' ( https://stackoverflow.com/u/733921/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Using @ EnvironmentObject in SwiftUI

SwiftUI has transformed how we create user interfaces for applications. One of its standout features is the ability to manage shared state using @ EnvironmentObject. However, not everyone finds this feature straightforward, especially when dealing with multiple classes. If you're encountering a crash related to @ EnvironmentObject, especially while attempting to access it from a secondary class, you're not alone. Let's explore this issue in detail and find a solution together.

The Problem

In your SwiftUI app, you might want to share data across different views or classes seamlessly. For instance, you might have a MeetingStats class containing stats for a meeting, and a Meeting class that processes these stats. The goal is for changes made in one view (like a settings view) to reflect in another (such as a meeting processing view).

Here’s a brief summary of the crash issue you encountered:

You set up @ EnvironmentObject in your main view (Container or ContentView).

Upon accessing the MeetingStats object from the Meeting class, you received a crash message: "No ObservableObject of type MeetingStats found."

This error indicates that the SwiftUI environment can't find the MeetingStats object that you've supposedly passed down the view hierarchy.

Solution Steps

1. Correctly Define Your @ EnvironmentObject

Ensure that your secondary class, in this case Meeting, is declared to use @ EnvironmentObject. This is vital because without this declaration, the class won't automatically be able to access the environment object.

In your Meeting class, you need to redefine where @ EnvironmentObject is being utilized. It should not be directly in a model class like Meeting. Instead, it should be declared in your view object. Here’s how you could do that correctly:

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2. Pass the Environment Object Explicitly

Instead of having Meeting class directly access @ EnvironmentObject, pass it as an argument. Modify the calcQuorumEvents function to accept MeetingStats as a parameter. This ensures that the Meeting class can work with a valid instance of MeetingStats:

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3. Ensure Proper Setup in Your Views

In your iOSMeetingView, you need to ensure both the MeetingStats and Meeting objects are explicitly passed through the environment. Here’s how you can define it properly in your SwiftUI view:

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Then, in your tab view (often defined in ContentView or similar), make sure to pass the needed environment objects:

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4. Verify Your Scene Delegate Setup

Double-check the SceneDelegate to confirm that you're properly creating and passing MeetingStats and Meeting to the root view:

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Conclusion

Using @ EnvironmentObject in SwiftUI can initially be confusing, especially when dealing with multiple classes or instances. By correctly declaring your environment objects, passing them explicitly where needed, and managing your view hierarchy effectively, you can avoid common pitfalls like accessing non-existent objects.

Following these steps should help you resolve the crashing issue and keep your application's state synchronized across different views. Happy coding!