Solving the @ EnvironmentObject Issue in SwiftUI: How to Properly Manage a Global Cart Array

Discover how to effectively manage a global array in SwiftUI using the `@ EnvironmentObject`. Learn to preserve state across views and ensure your data persists for seamless user experience!
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This video is based on the question https://stackoverflow.com/q/69628795/ asked by the user 'Honey' ( https://stackoverflow.com/u/1719339/ ) and on the answer https://stackoverflow.com/a/69663950/ provided by the user 'jnpdx' ( https://stackoverflow.com/u/560942/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Solving the @ EnvironmentObject Issue in SwiftUI

When working with SwiftUI, many developers face challenges managing state across their views. One common issue is related to the use of the @ EnvironmentObject property, especially when it comes to sharing data globally. In this guide, we will dive into a specific problem regarding updating and preserving a cart array in a SwiftUI application, and propose a solution that ensures your data remains accessible from any view.

The Problem

Imagine you're building a SwiftUI application that includes a shopping cart feature. You have a DataStorage class designed as a global state manager, allowing you to share data (like your cart items) between various views. However, after implementing your Views, you realize that:

Adding books to the cart using your ViewModel (addBook function) doesn’t retain the previous items.

Every time the View1 is accessed, a new instance of DataStorage seems to be created, leading to an empty cart on subsequent accesses.

Here’s a brief summary of the observed behavior:

On the first addition of a book, the cart displays only that book.

When returning to View1 and adding another book, it creates a new instance of DataStorage, resulting in a cart that shows just that book.

The Solution

Use a Single Instance of DataStorage

The key to resolving this issue is to ensure that you maintain a single instance of the DataStorage class throughout your application. This can be achieved by correctly using the .environmentObject modifier to inject your instance at the root of your view hierarchy.

Steps to Implement the Solution

Create One Instance of DataStorage
Move the creation of the DataStorage instance to your main application:

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

Modify the ViewModel to Use the Injected Instance
Rather than instantiating a new DataStorage inside your ViewModel, allow it to receive the shared instance through an optional property:

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

Pass the Environment Object
In your View1, utilize the onAppear modifier to set the dataStorage in your ViewModel:

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

Display the Cart Contents
Lastly, in your View3, you can access the cartArray seamlessly:

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

Conclusion

By ensuring that you have a single, shared instance of DataStorage, you can effectively manage your app's state and persist data across multiple views. This approach not only resolves the problem of data not being retained but also enhances the user experience by providing consistent access to cart contents.

Implementing the @ EnvironmentObject correctly allows you to build a robust SwiftUI application that handles state management effectively. Happy coding!