How do I use UserDefaults with SwiftUI?

Question

struct ContentView: View {
@State var settingsConfiguration: Settings
    struct Settings {
        var passwordLength: Dou         


        

Answer 1

Starting from Xcode 12.0 (iOS 14.0) you can use @AppStorage property wrapper for such types: Bool, Int, Double, String, URL and Data. Here is example of usage for storing String value:

struct ContentView: View {
    
    static let userNameKey = "user_name"
    
    @AppStorage(Self.userNameKey) var userName: String = "Unnamed"
    
    var body: some View {
        VStack {
            Text(userName)
            
            Button("Change automatically ") {
                userName = "Ivor"
            }
            
            Button("Change manually") {
                UserDefaults.standard.setValue("John", forKey: Self.userNameKey)
            }
        }
    }
}

Here you are declaring userName property with default value which isn't going to the UserDefaults itself. When you first mutate it, application will write that value into the UserDefaults and automatically update the view with the new value.

Also there is possibility to set custom UserDefaults provider if needed via store parameter like this:

@AppStorage(Self.userNameKey, store: UserDefaults.shared) var userName: String = "Mike"

and

extension UserDefaults {
    static var shared: UserDefaults {
        let combined = UserDefaults.standard
        combined.addSuite(named: "group.myapp.app")
        return combined
    }
}

Notice: ff that value will change outside of the Application (let's say manually opening the plist file and changing value), View will not receive that update.

P.S. Also there is new Extension on View which adds func defaultAppStorage(_ store: UserDefaults) -> some View which allows to change the storage used for the View. This can be helpful if there are a lot of @AppStorage properties and setting custom storage to each of them is cumbersome to do.

Answer 2

First, create a property wrapper that will allow us to easily make the link between your Settings class and UserDefaults:

import Foundation

@propertyWrapper
struct UserDefault<Value: Codable> {    
    let key: String
    let defaultValue: Value

    var value: Value {
        get {
            let data = UserDefaults.standard.data(forKey: key)
            let value = data.flatMap { try? JSONDecoder().decode(Value.self, from: $0) }
            return value ?? defaultValue
        }
        set {
            let data = try? JSONEncoder().encode(newValue)
            UserDefaults.standard.set(data, forKey: key)
        }
    }
}

Then, create a data store that holds your settings:

import Combine
import SwiftUI

final class DataStore: BindableObject {
    let didChange = PassthroughSubject<DataStore, Never>()

    @UserDefault(key: "Settings", defaultValue: [])
    var settings: [Settings] {
        didSet {
            didChange.send(self)
        }
    }
}

Now, in your view, access your settings:

import SwiftUI

struct SettingsView : View {
    @EnvironmentObject var dataStore: DataStore

    var body: some View {
        Toggle(isOn: $settings.space) {
            Text("\(settings.space)")
        }
    }
}

Answer 3

If you are persisting a one-off struct such that a property wrapper is overkill, you can encode it as JSON. When decoding, use an empty Data instance for the no-data case.

final class UserData: ObservableObject {
    @Published var profile: Profile? = try? JSONDecoder().decode(Profile.self, from: UserDefaults.standard.data(forKey: "profile") ?? Data()) {
        didSet { UserDefaults.standard.set(try? JSONEncoder().encode(profile), forKey: "profile") }
    }
}

Answer 4

The approach from caram is in general ok but there are so many problems with the code that SmushyTaco did not get it work. Below you will find an "Out of the Box" working solution.

1. UserDefaults propertyWrapper

import Foundation
import Combine

@propertyWrapper
struct UserDefault<T> {
    let key: String
    let defaultValue: T
    
    init(_ key: String, defaultValue: T) {
        self.key = key
        self.defaultValue = defaultValue
    }
    
    var wrappedValue: T {
        get {
            return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
        }
        set {
            UserDefaults.standard.set(newValue, forKey: key)
        }
    }
}

2. UserSettings class

final class UserSettings: ObservableObject {

    let objectWillChange = PassthroughSubject<Void, Never>()

    @UserDefault("ShowOnStart", defaultValue: true)
    var showOnStart: Bool {
        willSet {
            objectWillChange.send()
        }
    }
}

3. SwiftUI view

struct ContentView: View {

@ObservedObject var settings = UserSettings()

var body: some View {
    VStack {
        Toggle(isOn: $settings.showOnStart) {
            Text("Show welcome text")
        }
        if settings.showOnStart{
            Text("Welcome")
        }
    }
}

Answer 5

The code below adapts Mohammad Azam's excellent solution in this video:

import SwiftUI

struct ContentView: View {
    @ObservedObject var userDefaultsManager = UserDefaultsManager()

    var body: some View {
        VStack {
            Toggle(isOn: self.$userDefaultsManager.firstToggle) {
                Text("First Toggle")
            }

            Toggle(isOn: self.$userDefaultsManager.secondToggle) {
                Text("Second Toggle")
            }
        }
    }
}

class UserDefaultsManager: ObservableObject {
    @Published var firstToggle: Bool = UserDefaults.standard.bool(forKey: "firstToggle") {
        didSet { UserDefaults.standard.set(self.firstToggle, forKey: "firstToggle") }
    }

    @Published var secondToggle: Bool = UserDefaults.standard.bool(forKey: "secondToggle") {
        didSet { UserDefaults.standard.set(self.secondToggle, forKey: "secondToggle") }
    }
}