Handle Auth state in WindowGroup - ios

Question

I'm new to SwiftUI still and don't really know how to handle best the auth state. If a user is logged in for example i want to redirect him to home screen if not to a certain screen.
I have a service that will tell me if the user is authenticated like: self.authService.isAuthenticated but in my App in WindowGroup i cannot use my service since this is all a struct and i get Cannot use mutating getter on immutable value: 'self' is immutable
I would appreciate a little snippet that can help me solve this here.
My code:
#main
struct MyApp: App, HasDependencies {
#UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
// MARK: Services
private lazy var authService: AuthService = dependencies.authService()
var body: some Scene {
WindowGroup {
if !self.authService.isAuthenticated {
WelcomeView()
} else {
MainView()
}
}
}
}

Answer 1

I suppose you want to handle it just for this time, but i'm proposing you look deeper in SwiftUI bindings and state handlings.
So here we just save the value in a variable in the init since this is getting loaded first.
#main
struct MainApp: App, HasDependencies {
#UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
// MARK: Services
private lazy var authService: AuthService = dependencies.authService()
var isAuth: Bool = false
init() {
isAuth = self.authService.isAuthenticated
}
var body: some Scene {
WindowGroup {
if isAuth {
MainView()
} else {
WelcomeView()
}
}
}
}

Answer 2

The problem is
private lazy var authService: AuthService = dependencies.authService()
(A) SwiftUI rebuilds views in response to, for example, a #StateObject's ObjectWillChangePublisher. Changes an unwatched variable fall silently in a forest without participating in this UI framework, but would be read if you trigger a state change by some other object. Also, I'd guess that service will be rebuilt every time the struct is first built, but I haven't had a use case for this scenario yet, so I don't know.
(B) You've got a mutating variable holding a reference type stored in a value type. As above, store your service as an #StateObject, which is one way SwiftUI gets around this problem of lifetime management.
To get "lazy" loading, call .onAppear { service.load() }.
That said, you have a services / factory container you probably already want to be an #StateObject and injected into the environment. If you store an ObservableObject inside an ObservableObject, the View will react to the outer object only. That object does not link its ObjectWillChangePublisher to inner objects. You will need to either:
(a) individually inject select services into the environment for children to observe
(b) pass those into observable view models that use Combine to subscribe to specific states
(c) use .onReceive and .onChange APIs on Views to link to specific state changes
(C) Conditionals evaluated in App can cause objects stored in that struct to be rebuilt. Good practice is to keep App super clean, like always. Move any conditional logic to a "Root" View for that Scene.