How to create a singleton that I can update in SwiftUI - ios

Question

I want to create a global variable for showing a loadingView, I tried lots of different ways but could not figure out how to. I need to be able to access this variable across the entire application and update the MotherView file when I change the boolean for the singleton.
struct MotherView: View {
#StateObject var viewRouter = ViewRouter()
var body: some View {
if isLoading { //isLoading needs to be on a singleton instance
Loading()
}
switch viewRouter.currentPage {
case .page1:
ContentView()
case .page2:
PostList()
}
}
}
struct MotherView_Previews: PreviewProvider {
static var previews: some View {
MotherView(viewRouter: ViewRouter())
}
}
I have tried the below singleton but it does not let me update the shared instance? How do I update a singleton instance?
struct LoadingSingleton {
static let shared = LoadingSingleton()
var isLoading = false
private init() { }
}

Answer 1

Make your singleton a ObservableObject with #Published properties:
struct ContentView: View {
#StateObject var loading = LoadingSingleton.shared
var body: some View {
if loading.isLoading {
Text("Loading...")
}
ChildView()
Button(action: { loading.isLoading.toggle() }) {
Text("Toggle loading")
}
}
}
struct ChildView : View {
#StateObject var loading = LoadingSingleton.shared
var body: some View {
if loading.isLoading {
Text("Child is loading")
}
}
}
class LoadingSingleton : ObservableObject {
static let shared = LoadingSingleton()
#Published var isLoading = false
private init() { }
}
I should mention that in SwiftUI, it's common to use .environmentObject to pass a dependency through the view hierarchy rather than using a singleton -- it might be worth looking into.

Answer 2

First, make LoadingSingleton a class that adheres to the ObservableObject protocol. Use the #Published property wrapper on isLoading so that your SwiftUI views update when it's changed.
class LoadingSingleton: ObservableObject {
#Published var isLoading = false
}
Then, put LoadingSingleton in your SceneDelegate and hook it into your SwiftUI views via environmentObject():
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
var window: UIWindow?
static let singleton = LoadingSingleton()
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
let contentView = ContentView()
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView.environmentObject(SceneDelegate.singleton))
self.window = window
window.makeKeyAndVisible()
}
}
}
To enable your SwiftUI views to update when changing isLoading, declare a variable in the view's struct, like this:
struct MyView: View {
#EnvironmentObject var singleton: LoadingSingleton
var body: some View {
//Do something with singleton.isLoading
}
}
When you want to change the value of isLoading, just access it via SceneDelegate.singleton.isLoading, or, inside a SwiftUI view, via singleton.isLoading.