How to use AppStorage Property to communicate with UserDefaults and update SwiftUI view. New in iOS 14…

struct ContentView: View {
    @AppStorage("notificationsOn") var notificationsOn: Bool = false

    var body: some View {
        VStack {
            Toggle(isOn: $notificationsOn){
               Text("Notifications ON")
            }.padding()
            Text("Notifications \(notificationsOn ? "ON" : "OFF")")
        }
    }
}

Toggling value of notificationsOn will cause boolean value directly to be written to UserDefaults Changes in UserDefaults for the property notificationsOn would invalidate body and triggers view update.

Note: By default AppStorage utilizes standard user defaults, we can use alternate initializer to specify different user defaults if needed.

init(_ key: String, store: UserDefaults? = nil) where Value == Int?

i.e.

@AppStorage("notificationsOn", UserDefaults(suiteName: "com.app.settings")) var notificationsOn: Bool = false

Note: AppStorage Property Wrapper is released as part of SwiftUI framework.