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What is the @AppStorage property wrapper?

Paul Hudson    @twostraws   

Updated for Xcode 12.0

New in iOS 14

SwiftUI has a dedicated property wrapper for reading values from UserDefaults, which will automatically reinvoke your view’s body property when the value changes. That is, this wrapper effectively watches a key in UserDefaults, and will refresh your UI if that key changes.

For example, this will watch UserDefaults for a “username” key, which will be set when the button is pressed:

struct ContentView: View {
    @AppStorage("username") var username: String = "Anonymous"

    var body: some View {
        VStack {
            Text("Welcome, \(username)!")

            Button("Log in") {
                self.username = "@twostraws"
            }
        }
    }
}

Changing username above will cause the new string to be written to UserDefaults immediately, while also updating the view. The same would be true if we had used the older method:

UserDefaults.standard.set("@twostraws", forKey: "username")`

@AppStorage will watch UserDefaults.standard by default, but you can also make it watch a particular app group if you prefer, like this:

@AppStorage("username", store: UserDefaults(suiteName: "group.com.hackingwithswift.unwrap")) var username: String = "Anonymous"
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