SwiftUI: How to persist @Published variable using UserDefaults?

Question

I want a @Published variable to be persisted, so that it's the same every time when I relaunch my app.

I want to use both the @UserDefault and @Published property wrappers on one variable. For example I need a '@PublishedUserDefault var isLogedIn'.

I have the following propertyWrapper

import Foundation

@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)
        }
    }
}

This is my Settings class

import SwiftUI
import Combine

 class Settings: ObservableObject {

   @Published var isLogedIn : Bool = false

 func doLogin(params:[String:String]) {

        Webservice().login(params: params) { response in

            if let myresponse = response {                    
                    self.login = myresponse.login
                    }
               }
         }

}

My View class

struct HomeView : View {
    @EnvironmentObject var settings: Settings
    var body: some View {
        VStack {
            if settings.isLogedIn {
            Text("Loged in")
            } else{
            Text("Not Loged in")
            }
        }
    }
}

Is there a way to make a single property wrapper that covers both the persisting and the publishing?

Answer 1

To persist your data you could use the @AppStorage property wrapper. However, without using @Published your ObservableObject will no longer put out the news about the changed data. To fix this, simply call objectWillChange.send() from the property's willSet observer.

import SwiftUI

class Settings: ObservableObject {
    @AppStorage("Example") var example: Bool = false {
        willSet {
            // Call objectWillChange manually since @AppStorage is not published
            objectWillChange.send()
        }
    }
}

Answer 2

private var cancellables = [String:AnyCancellable]()

extension Published {
    init(wrappedValue defaultValue: Value, key: String) {
        let value = UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue
        self.init(initialValue: value)
        cancellables[key] = projectedValue.sink { val in
            UserDefaults.standard.set(val, forKey: key)
        }
    }
}

class Settings: ObservableObject {
    @Published(key: "isLogedIn") var isLogedIn = false
    ...
}

Sample: https://youtu.be/TXdAg_YvBNE

Version for all Codable types check out here