SwiftUI Combine: @Published is only available on properties of classes

Question

I have the following code and Im getting the message error:

'wrappedValue' is unavailable: @Published is only available on properties of classes

//*
/**
Chat
Created on 29/07/2020
*/

import SwiftUI

let lightGreyColor = Color(red: 239.0/255.0, green: 243.0/255.0, blue: 244.0/255.0, opacity: 1.0)

struct ConnectionView: View {
    @ObservedObject var keyboardResponder = KeyboardResponder()
    @ObservedObject var viewModel = ConnectionVM()
//    @State var uuid1: String = ""
//    @State var uuid2: String = ""
    @State var authenticationDidFail: Bool = false
    
    var body: some View {
        return VStack {
            WelcomeText()
            LogoImage()
            UUIDTextField(uuid: viewModel.uuid1)
            UUIDTextField(uuid: viewModel.uuid2)
            if authenticationDidFail {
                Text("Information not correct. Try again.")
                .offset(y: -10)
                .foregroundColor(.red)
            }
            Button(action: {
                print("Button tapped")
            }) {
               LoginButtonContent()
            }
        }
        .padding()
        .offset(y: -keyboardResponder.currentHeight*0.5)
    }
    struct WelcomeText : View {
        var body: some View {
            return Text("Welcome!")
                .font(.largeTitle)
                .fontWeight(.semibold)
                .padding(.bottom, 20)
        }
    }
    struct LogoImage : View {
        var body: some View {
            return Image("logo")
                .resizable()
                .aspectRatio(contentMode: .fill)
                .frame(width: 150, height: 150)
                .clipped()
                .cornerRadius(150)
                .padding(.bottom, 75)
        }
    }
    struct UUIDTextField : View {
        @Published var uuid: String
        var body: some View {
        return TextField("UUID", text: $uuid)
                    .padding()
                    .background(lightGreyColor)
                    .cornerRadius(5.0)
                    .padding(.bottom, 20)
            }
    }
    struct LoginButtonContent : View {
        var body: some View {
            return Text("LOGIN")
                .font(.headline)
                .foregroundColor(.white)
                .padding()
                .frame(width: 220, height: 60)
                .background(Color.green)
                .cornerRadius(15.0)
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ConnectionView()
    }
}

My question is

how can I pass @Published var by parameter to a subview .

Update Question

If i use Binding instead of published I get this error:

Cannot convert value of type 'String' to expected argument type 'Binding'

Parsnip

Answer 1

@Published can only be used in classes and sub View is a struct. You should use @Binding instead of @Published to pass a binding variable to a sub View.

struct UUIDTextField : View {
    @Binding var uuid: String
    var body: some View {
        return TextField("UUID", text: $uuid)
            .padding()
            .background(lightGreyColor)
            .cornerRadius(5.0)
            .padding(.bottom, 20)
    }
}

Then use binding to the passed on parameter.

UUIDTextField(uuid: $viewModel.uuid1)
UUIDTextField(uuid: $viewModel.uuid2)

Jataka

When I use binding instead of published i get this error: Cannot convert value of type 'String' to expected argument type 'Binding<String>' – Parsnip

Use binding. Add $ to the variable. Check the update. – Jataka

Answer 2

If you're getting this in a View Model, you probably mistakenly defined it as a struct -- and not a class that extends ObservableObject

Brainsick