SynchronizedDefaults.swift

/**
Example SwiftUI which synchronizes GUI toggles as booleans and stores them in UserDefaults

Mostly from the answer here: 
https://stackoverflow.com/questions/56822195/how-do-i-use-userdefaults-with-swiftui
*/

import SwiftUI
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)
        }
    }
}

class UserSettings: ObservableObject {
    let objectWillChange = PassthroughSubject<Void, Never>()
    
    @UserDefault("Foo", defaultValue: true)
    var foo: Bool {
        willSet {
            objectWillChange.send()
        }
    }
    
    @UserDefault("Bar", defaultValue: false)
    var bar: Bool {
        willSet {
            objectWillChange.send()
        }
    }
}

struct ContentView: View {
    @ObservedObject var settings = UserSettings()
    var body: some View {
        VStack {
            HStack {
                Toggle("toggle-foo",isOn: $settings.foo).toggleStyle(SwitchToggleStyle())
                Text(settings.foo ? "Foo:On!" : "Foo:Off!")
            }
            HStack{
                Toggle("toggle-bar",isOn: $settings.bar).toggleStyle(SwitchToggleStyle())
                Text(settings.bar ? "Bar:On!" : "Bar:Off!")
            }
        }.frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}