SwiftUI 从 ViewModel 访问全局状态

Question

I am experimenting with SwiftUI and having a hard time figuring out the proper architecture for my app.

What I am trying to achieve is simple. I want to have an initial screen that either show a sign up screen or the home screen for a given user depending on current authentication state. I cannot figure out how to make the initial screen pick up changes from the sign up screen once authentication has taken place. Here's some relevant code:

struct InitialView: View {
    @EnvironmentObject var viewModel: InitialViewModel

    var body: some View {
        VStack {
            if viewModel.auth.identity != nil {
                NewHomeView()
            } else {
                SignInView()
            }
        }
    }
}

In the sign in view, I have a usual sign in form and when the user presses the sign in button, I want to send a login request to the backend and remember the resulting token.

class SignInViewModel: ObservableObject {
    private let auth: AuthStore
    private let signInApi: SignInApi
    private var cancellableSet: Set<AnyCancellable>

    // Input
    @Published var name: String = ""
    @Published var password: String = ""
    @Published var showSignUp: Bool = false

    // Output
    @Published var authSuccess: Bool = false

    init(auth: AuthStore, signInApi: SignInApi) {
        self.auth = auth
        self.signInApi = signInApi
        self.cancellableSet = Set<AnyCancellable>()
    }

    func signIn() {
        signInApi.signIn(email: name, password: password).sink(receiveCompletion: { _ in }) { response in
            self.auth.identity = Identity(
                person: Person(id: 1, name: "user", sex: nil, birthday: nil),
                token: response.token
            )
            self.authSuccess = true
        }.store(in: &cancellableSet)
    }
}

HOWEVER, this does not work. Even after clicking the sign in button, the initial view is not updated. Note that I am passing the same AuthStore to both view models.

  let auth = AuthStore()

        // Create the SwiftUI view that provides the window contents.
        let contentView = InitialView()
            .environmentObject(InitialViewModel(auth: auth))
            .environmentObject(SignInViewModel(auth: auth, signInApi: SignInApi()))

where AuthStore is defined as

class AuthStore: ObservableObject {
    @Published var identity: Identity? = nil
}

Ideally, I'd love to be able to 1) have each view be paired with its own VM 2) have each VM access global state via @EnvironmentObject. However, it seems that @EnvironmentObject is restricted to views only? If so, how do I access the global auth state from within each VM that requires it?

Answer 1

As on provided code I would change it as following

struct InitialView: View {
    @EnvironmentObject var viewModel: InitialViewModel
    @EnvironmentObject var signIn: SignInViewModel

    var body: some View {
        VStack {
            if signIn.authSuccess {
                NewHomeView()
            } else {
                SignInView()
            }
        }
    }
}

as well redirect publisher to main thread in

    signInApi.signIn(email: name, password: password)
        .receive(on: RunLoop.main) // << following update should be on main thread
        .sink(receiveCompletion: { _ in }) { response in
        self.auth.identity = Identity(
            person: Person(id: 1, name: "user", sex: nil, birthday: nil),
            token: response.token
        )
        self.authSuccess = true
    }.store(in: &cancellableSet)

Answer 2

Venture a guess here since you didn't provide InitialViewModel details.

You didn't observe auth in SignInViewModel , and didn't publish it to tigger view update.

I'm guessing it's the same problem with InitialViewModel.

class SignInViewModel: ObservableObject {
    private let auth: AuthStore
    private let signInApi: SignInApi

To question 2): you can't. (as far as I know)

To question 1): you can. But at what cost? Are there better alternatives?

I can elaborate more if needed.