Скачать или смотреть Accessing a Published Variable Across Classes in SwiftUI

Learn how to access a `Published variable` from one class in another within SwiftUI. This step-by-step guide breaks down the solution using ObservableObject and explains crucial concepts with clear examples.
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Accessing a Published Variable Across Classes in SwiftUI

As you dive into the world of Swift and SwiftUI, you may encounter some challenges, especially when managing data across different classes. A common problem is accessing a published variable from an ObservableObject in another class. This post addresses that issue and provides a detailed guide on how to effectively share data between classes.

The Problem: Accessing a Published Variable

In this scenario, you have a class named PeriodViewModel where a variable is marked as @Published. This means any changes to this variable will cause the views observing it to refresh automatically. However, you also have another class, DataViewModel, where you want to access the updated value of the published variable from PeriodViewModel. Here is the code structure for better understanding:

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The goal is to retrieve updates from periodViewModel.value inside your DataViewModel.

Solution: Using @ObservedObject

Step 1: Understanding ObservableObject and Published

In SwiftUI, @ObservableObject is used to declare a class as an object that will notify its subscribers about changes. @Published is used to declare properties where changes will trigger observers' updates.

Step 2: Set Up Your DataViewModel

Create a Property: Ensure you have an @ObservedObject property in your DataViewModel that holds an instance of PeriodViewModel.

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Access the Value: Inside DataViewModel, you can access periodViewModel.value directly. Any changes in periodViewModel.value will automatically notify the view that observes DataViewModel.

Step 3: Update the UI

Here's how you can create a function to access and display the updated variable:

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Example of Using Completion Handlers

To further clarify data management between ViewModels, consider an example that involves a FirebaseDatabaseManager class used for saving data asynchronously. The completion handler can be beneficial for updating the @Published properties in your ObservableObject class.

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Conclusion

Accessing a published variable from one class in another isn't just about having the right declarations; it's also about understanding the SwiftUI lifecycle and leveraging @ObservedObject correctly. By following the steps outlined above, you can efficiently share data across different parts of your app and keep your UI synchronized with your data changes.

We hope this guide will clear up any confusion regarding published variables and encourage you to explore more functionality in SwiftUI!

If you have more questions or need further assistance, feel free to reach out or leave a comment below!