How to access UserDefaults using AppStorage property wrapper

WWDC20 SwiftUI updates straight forwards UserDefaults access by introducing @AppStorage property wrapper. This article will explain how to store and read simple types like integer, string, double, data, or URL.

Learn how to store other types like Date using RawRepresentable

UserDefaults is a simple key-value storage that can be used to store a limited number of simple values. It is a simple persistence system where you can store user preferences or other, no critical, small data preserved between application runs.

To use @AppStorage, you have to wrap a property within your view with it. The only parameter that has to be specified is a string - the name of your key. Swift will deduce a type from a property itself.

@AppStorage("valueKey") var value: Int = 0

Your @AppStorage UserDefaults property is ready to use. You can read it and modify it in body function.

var body: some View {
    VStack {
        Text("Value: \(value)")
        Button("Increment") { value += 1 }
    }
}

When you change a property on one screen, any other that uses this property will also be refreshed. You can test it on that simple example.

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            ViewA()
            ViewB()
        }
    }
}

struct ViewA: View {
    @AppStorage("valueKey") var value: Int = 0
    
    var body: some View {
        VStack {
            Text("ViewA value: \(value)")
            Button("Increment") { value += 1 }
        }
    }
}

struct ViewB: View {
    @AppStorage("valueKey") var value: Int = 0
    
    var body: some View {
        VStack {
            Text("ViewB value: \(value)")
            Button("Decrement") { value -= 1 }
        }
    }
}

There is one additional detail worth mentioning — UserDefaults support different databases. By default, @AppStorage uses UserDefaults.standard, but you can create your own by providing it as a store parameter.

@AppStorage("valueKey", store: UserDefaults(suiteName: "com.swiftwombat.customStore")) var value: Int = 0

Values in different databases (created by providing a suite name) are not connected and can have the same key. Modifying value in the standard defaults doesn't alter the value in custom defaults.

Want to test it yourself? Download this Xcode project.