AppStorage
@AppStorage is a convenient way to save and read variables from UserDefaults and use them in the same way as @State properties. It can be seen as a @State property which is automatically saved to (and read from) UserDefaults.
You can think of the following:
@AppStorage("emailAddress") var emailAddress: String = "[email protected]"
as an equivalent of this (which is not allowed in SwiftUI and will not compile):
@State var emailAddress: String = "[email protected]" {
get {
UserDefaults.standard.string(forKey: "emailAddress")
}
set {
UserDefaults.standard.set(newValue, forKey: "emailAddress")
}
}
Note that @AppStorage behaves like a @State: a change to its value will invalidate and redraw a View.
By default @AppStorage will use UserDefaults.standard. However, you can specify your own UserDefaults store:
@AppStorage("emailAddress", store: UserDefaults(...)) ...
Unsupported types (e.g., Array):
As mentioned in iOSDevil’s answer, AppStorage is currently of limited use:
types you can use in @AppStorage are (currently) limited to: Bool, Int, Double, String, URL, Data
If you want to use any other type (like Array), you can add conformance to RawRepresentable:
extension Array: RawRepresentable where Element: Codable {
public init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let result = try? JSONDecoder().decode([Element].self, from: data)
else {
return nil
}
self = result
}
public var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let result = String(data: data, encoding: .utf8)
else {
return "[]"
}
return result
}
}
Demo:
struct ContentView: View {
@AppStorage("itemsInt") var itemsInt = [1, 2, 3]
@AppStorage("itemsBool") var itemsBool = [true, false, true]
var body: some View {
VStack {
Text("itemsInt: \(String(describing: itemsInt))")
Text("itemsBool: \(String(describing: itemsBool))")
Button("Add item") {
itemsInt.append(Int.random(in: 1...10))
itemsBool.append(Int.random(in: 1...10).isMultiple(of: 2))
}
}
}
}