尝试传递 state 变量以自动更新 SwiftUI 中的视图

Question

I have a variable that holds the state of whether or not a certain type of session is active. This is used to determine which view is shown. I want my view model to post a document, toggle this state, and then automatically update the view. However, the view is not updating.

So this is the base layer of the view that I have. sessionState starts as false and defaults to the StartSessionView to initialize a session. If one is active, it goes to GroupSessionView.

struct SessionView: View {
    @State var sessionState = false

    @ViewBuilder
    var body: some View {
        if sessionState {
            StartSessionView(sessionState: $sessionState)
        } else {
            GroupSessionView(sessionState: $sessionState)
        }
    }
}

The StartSessionView page has the following code. The important thing here is the sessionManager view model. I initialize a SessionManager with a Session object (not important as that part is working), and a sessionState.

struct StartSessionView: View {
    @State var sessionManager = SessionManager(session: Session(sessionType: ""), sessionState: false)
    @ObservedObject var userViewModel = AuthViewModel()
       
    @Binding var sessionState: Bool
            
    var body: some View {
        VStack(alignment: .leading, spacing: 40) {
            Button {
                sessionManager = SessionManager(session: Session(sessionType: dropdownValue), sessionState: sessionState)
                sessionManager.startSession()
                
                
            } label: {
                Text("Do stuff")      
            }
   
        }
    }
}

And finally, this is the view model.

class SessionManager: ObservableObject {

    @State var sessionState: Bool
    let session: Session
    
    init(session: Session, sessionState: Bool) {
        self.session = session
        self.sessionState = sessionState
    }
    
    func startSession() {
        
        var messageData = ["sessionType": session.sessionType]
        
        let document = Firestore.firestore()
            .collection("sessions")
            .document()
        
        document.setData(messageData) {error in
            if let error = error {
                print(error)
                return
            } else { sessionState.toggle }
 
            
        }
        
    }
}

So when the sessionState is toggled here, I want this to be passed back to the SessionView struct, see that sessionState = true, and go to the GroupSessionView. I'm not sure how to pass this data through so many layers though.

Answer 1

Oops, It seems you missing something. @State only works with variable, structs.. and not a class in this case . And if you want to pass data to another view you could be using the environment in SwiftUI.

        struct SessionView: View {
            @State var sessionState = false
            @StateObject var someThingKeepManager = SomeThingKeepManager()
            @ViewBuilder
            var body: some View {
                ZStack {
                    if sessionState {
                        StartSessionView(sessionState: $sessionState)
                    } else {
                        GroupSessionView(sessionState: $sessionState)
                    }
                }
                .environmentObject(someThingKeepManager)
            }
        }