Cannot convert value of type 'Published<Bool>.Publisher' to expected argument type 'Binding<Bool>'

user_14059662 0
Viewed 23817

When trying to compile the following code:

class LoginViewModel: ObservableObject, Identifiable {
    @Published var mailAdress: String = ""
    @Published var password: String = ""
    @Published var showRegister = false
    @Published var showPasswordReset = false

    private let applicationStore: ApplicationStore

    init(applicationStore: ApplicationStore) {
        self.applicationStore = applicationStore
    }

    var passwordResetView: some View {
        PasswordResetView(isPresented: $showPasswordReset) // This is where the error happens
    }
}

Where PasswordResetView looks like this:

struct PasswordResetView: View {
    @Binding var isPresented: Bool
    @State var mailAddress: String = ""
    
    var body: some View {
            EmptyView()
        }
    }
}

I get the error compile error

Cannot convert value of type 'Published<Bool>.Publisher' to expected argument type 'Binding<Bool>'

If I use the published variable from outside the LoginViewModel class it just works fine:

struct LoginView: View {
    @ObservedObject var viewModel: LoginViewModel

    init(viewModel: LoginViewModel) {
      self.viewModel = viewModel
    }
    
    var body: some View {
            PasswordResetView(isPresented: self.$viewModel.showPasswordReset)
    }
}

Any suggestions what I am doing wrong here? Any chance I can pass a published variable as a binding from inside the owning class?

Thanks!

combine swiftui swift ios
5 Answers

Not sure why the proposed solutions here are so complex, when there is a very direct fix for this.

Found this answer on a similar Reddit question:

The problem is that you are accessing the projected value of an @Published (which is a Publisher) when you should instead be accessing the projected value of an @ObservedObject (which is a Binding), that is: you have globalSettings.$tutorialView where you should have $globalSettings.tutorialView.

user_19723720
user_4135940

I think the important thing to understand here is what "$" does in the Combine context.

What "$" does is to publish the changes of the variable "showPasswordReset" where it is being observed.

when it precedes a type, it doesn't represent the type you declared for the variable (Boolean in this case), it represents a publisher, if you want the value of the type, just remove the "$".

"$" is used in the context where a variable was marked as an @ObservedObject, (the ObservableObject here is LoginViewModel and you subscribe to it to listen for changes in its variables market as publishers)

struct ContentView: View {
       @ObservedObject var loginViewModel: LoginViewModel...

in that context (the ContentView for example) the changes of "showPasswordReset" are going to be 'Published' when its value is updated so the view is updated with the new value.

user_18792720

Here is possible approach - the idea to make possible observation in generated view and avoid tight coupling between factory & presenter.

Tested with Xcode 12 / iOS 14 (for older systems some tuning might be needed)

protocol ResetViewModel {
    var showPasswordReset: Bool { get set }
}

struct PasswordResetView<Model: ResetViewModel & ObservableObject>: View {
    @ObservedObject var resetModel: Model

    var body: some View {
        if resetModel.showPasswordReset {
            Text("Show password reset")
        } else {
            Text("Show something else")
        }
    }
}

class LoginViewModel: ObservableObject, Identifiable, ResetViewModel {
    @Published var mailAdress: String = ""
    @Published var password: String = ""
    @Published var showRegister = false
    @Published var showPasswordReset = false

    private let applicationStore: ApplicationStore

    init(applicationStore: ApplicationStore) {
        self.applicationStore = applicationStore
    }

    var passwordResetView: some View {
        PasswordResetView(resetModel: self)
    }
}
user_122990300

For error that states: "Cannot convert value of type 'Binding' to expected argument type 'Bool'" solution is to use wrappedValue as in example below.

If you have MyObject object with property isEnabled and you need to use that as vanilla Bool type instead of 'Binding' then do this myView.disabled($myObject.isEnabled.wrappedValue)

user_30570580
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