Скачать или смотреть How to Create and Persist a Global Variable in SwiftUI

Learn how to implement a `global variable` in SwiftUI that maintains its value even after your app closes. This guide provides a step-by-step approach to achieving this with proper structure.
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This video is based on the question https://stackoverflow.com/q/67551544/ asked by the user 'sUnit1' ( https://stackoverflow.com/u/15878457/ ) and on the answer https://stackoverflow.com/a/67551635/ provided by the user 'Roland Lariotte' ( https://stackoverflow.com/u/10408494/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Create and Persist a Global Variable in SwiftUI

When building applications in SwiftUI, managing state is a crucial aspect. One common issue developers face is creating a global variable that can be accessed across various parts of the app and persists even when the app is closed. In this guide, we will address the problem of how to implement a global variable, specifically one called "Quarters," that increments its value through user interaction and retains its value across app sessions.

The Problem

You may find yourself writing code where you attempt to create a global variable, but it does not behave as expected. For instance, you want a "Quarters" variable that starts at 0 and can be incremented every time a button is pressed. However, if the variable is set up as a simple global variable, it doesn't work—as it does not retain its value when you access it from different parts of the app or after closing the app.

Here's a quick example of a problem setup using SwiftUI:

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The above code will show "0" as the output, and the value of "quarters" will not increase as expected when the button is pressed.

The Solution: Implementing @ AppStorage

The key to solving this issue is utilizing SwiftUI's @ AppStorage property wrapper. This approach not only handles your variable effectively but also saves its value locally in the device storage, allowing it to persist across app closures.

Step 1: Refactor Your View

You'll need to use a view model for better state management. Instead of trying to reference the data directly from a struct, our view will reference a ViewModel that uses @ AppStorage:

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Step 2: Create a ViewModel

Now we need to create a GameViewModel class to manage the quarters data. This class will handle the logic and state needed for your global variable:

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

Explanation of @ AppStorage

Persistence: By declaring quarters with @ AppStorage, the value is automatically saved in UserDefaults. This means it is retained even after the app is closed.

Automatic Updates: Changes made to quarters will be automatically reflected in any view observing the ViewModel without the need for manual updates.

Conclusion

By using @ AppStorage in combination with a ViewModel, you can create a global variable in SwiftUI that is both accessible across different views and persists its value beyond app sessions. This approach not only enhances code readability but also simplifies state management in your applications.

Now you can incorporate this solution into your app development process and manage your global variables with ease. Happy coding!