Push View programmatically in callback, SwiftUI

Question

It seems to me that Apple is encouraging us to give up using UIViewController in SwiftUI, but without using view controllers, I feel a little bit powerless. What I would like is to be able to implement some sort of ViewModel which will emit events to View.

ViewModel:

public protocol LoginViewModel: ViewModel {
  var onError: PassthroughSubject<Error, Never> { get }
  var onSuccessLogin: PassthroughSubject<Void, Never> { get }
}

View:

public struct LoginView: View {
  fileprivate let viewModel: LoginViewModel
  
  public init(viewModel: LoginViewModel) {
    self.viewModel = viewModel
  }
  
  public var body: some View {
    NavigationView {
      MasterView()
        .onReceive(self.viewModel.onError, perform: self.handleError)
        .onReceive(self.viewModel.onSuccessLogin, perform: self.handleSuccessfullLogin)
    }
  }

  func handleSuccessfullLogin() {
    //push next screen
  }
  
  func handleError(_ error: Error) {
    //show alert
  }
}

Using SwiftUI, I don't know how to push another controller if login is successful

Also, I would appreciate any advice about how to implement what I want in a better way. Thanks.

Answer 1

I've found the answer. If you want to show another view on callback you should

1. Create state @State var pushActive = false

2. When ViewModel notifies that login is successful set pushActive to true

   func handleSuccessfullLogin() {
       self.pushActive = true
       print("handleSuccessfullLogin")
   }
   

3. Create hidden NavigationLink and bind to that state

   NavigationLink(destination: 
      ProfileView(viewModel: ProfileViewModelImpl()),
      isActive: self.$pushActive) {
        EmptyView()
   }.hidden()
   

Answer 2

I'm adding some snippets here because I think it simplifies some things and makes reusing navigation links easier:

1. Add View Navigation Extensions

extension View {
    func navigatePush(whenTrue toggle: Binding<Bool>) -> some View {
        NavigationLink(
            destination: self,
            isActive: toggle
        ) { EmptyView() }
    }

    func navigatePush<H: Hashable>(when binding: Binding<H>,
                                   matches: H) -> some View {
        NavigationLink(
            destination: self,
            tag: matches,
            selection: Binding<H?>(binding)
        ) { EmptyView() }
    }

    func navigatePush<H: Hashable>(when binding: Binding<H?>,
                                   matches: H) -> some View {
        NavigationLink(
            destination: self,
            tag: matches,
            selection: binding
        ) { EmptyView() }
    }
}

Now, you can call on any view (make sure they (or a parent) are in a navigation view)

2. Use at leisure

struct Example: View {
    @State var toggle = false
    @State var tag = 0

    var body: some View {
        NavigationView {
            VStack(alignment: .center, spacing: 24) {
                Text("toggle pushed me")
                    .navigatePush(whenTrue: $toggle)
                Text("tag pushed me (2)")
                    .navigatePush(when: $tag, matches: 2)
                Text("tag pushed me (4)")
                    .navigatePush(when: $tag, matches: 4)

                Button("toggle") {
                    self.toggle = true
                }

                Button("set tag 2") {
                    self.tag = 2
                }

                Button("set tag 4") {
                    self.tag = 4
                }
            }
        }
    }
}

Answer 3

as @Bhodan mentioned you can do it by changing state

Using EnvironmentObject with SwiftUI

1. Add UserData ObservableObject :

class UserData: ObservableObject, Identifiable {

    let id = UUID()
    @Published var firebase_uid: String = ""
    @Published var name: String = ""
    @Published var email: String = ""
    @Published var loggedIn: Bool = false
}

the loggedIn property will be used to monitor when a change in user logs in or out

2. Now add it as an @EnvironmentObject in your SceneDelegate.swift file in Xcode this just makes it so its accessible everywhere in your app

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?


    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        // Create the SwiftUI view that provides the window contents.
        let userData = UserData()
        let contentView = ContentView().environmentObject(userData)

        // Use a UIHostingController as window root view controller.
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }
    }

Once you make any change to the loggedIn property any UI that is Binded to it will respond to the true/false value change

the as @Bhodan mentioned just add this to your view and it will respond to that change

struct LoginView: View {
@EnvironmentObject var userData: UserData

var body: some View {
NavigationView {
VStack {
NavigationLink(destination: ProfileView(), isActive: self.$userData.loggedin) {
    EmptyView()
    }.hidden()
   }
  }
 }
}