How to create custom @Environment values in SwiftUI

With the @Environment property wrapper, we have the possibility to share data between SwiftUI views without explicitly passing the data from view to view.

Besides using the predefined values provided by SwiftUI, we can also create our own custom @Environment values using the following 3 steps:

1. Declaring a new environment key type:

private struct AnalyticsCategoryEnvironmentKey: EnvironmentKey {
    static let defaultValue: String = "none"
}

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2. Defining our environment value property by extending EnvironmentValues:

extension EnvironmentValues {
    var analyticsCategory: String {
        get { self[AnalyticsCategoryEnvironmentKey.self] }
        set { self[AnalyticsCategoryEnvironmentKey.self] = newValue }
    }
}

3. Now we can use the environment value in our views.

// Setting the environment value.
LoginView()
    .environment(\.analyticsCategory, "login")

// Accessing the environment value.
struct LoginView: View {
    @Environment(\.analyticsCategory) var analyticsCategory: String

    var body: some View {
        Text(analyticsCategory)
    }
}

Instead of a String, we can of course use any other type for the environment value.

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