State driven navigation

[zvona031]

I’m trying to make the app use state-driven navigation. Specifically, I want to present sheets and full-screen covers using an optional enum as the navigation state.

Based on the approach recommended here
, I tried using the navigate(to:) method. However, it’s not behaving as I expected, so I think I might be missing something.

What I’m doing is setting the destination object to a value, which correctly triggers the sheet presentation. Inside that sheet, I inject an onBack closure. When the back button is tapped, that closure sets the parent’s destination back to nil.

I would expect the sheet to dismiss at that point, but nothing happens.

After some investigation, I noticed that NavigateToModifier sets the destination to nil automatically after the navigation occurs. That made me wonder how I can achieve the behavior I’m describing, and whether it’s even possible to do so with this library.

struct RootView: View {
    @State private var viewModel = RootViewModel()
    
    var body: some View {
        ManagedNavigationStack {
            VStack {
                Button("Navigate to A") {
                    viewModel.navigateToA()
                }
            }
            .padding()
            .navigate(to: self.$viewModel.destination)
        }
    }
}

@Observable
final class RootViewModel {
    var destination: Destinations?
    
    func navigateToA() {
        self.destination = .a { [weak self] in
            self?.dismiss()
        }
    }
    
    func dismiss() {
        self.destination = nil
    }
}

struct AView: View {
    @State private var viewModel: AViewModel
    
    var body: some View {
        Button("Back") {
            viewModel.backTapped()
        }
    }
    
    init(onBack: @escaping () -> Void) {
        self._viewModel = State(wrappedValue: AViewModel(onBack: onBack))

    }
}

@Observable
class AViewModel {
    let onBack: () -> Void
    
    init(onBack: @escaping () -> Void) {
        self.onBack = onBack
    }

    func backTapped() {
        self.onBack()
    }
}

[hmlongco]

I have a version that respects nil for presentation dismissal, but that requires callbacks in the navigation tree and that breaks state restoration. Still thinking about that one

In the meantime, a common pattern for those who want callback handlers is to have action buttons pass the navigator into the method in question...

struct RootView: View {
    @State private var viewModel = RootViewModel()
    
    var body: some View {
        ManagedNavigationStack { navigator in
            VStack {
                Button("Navigate to A") {
                    viewModel.navigateToA(via: navigator)
                }
            }
            .padding()
            .navigate(to: self.$viewModel.destination)
        }
    }
}

@Observable
final class RootViewModel {
    var destination: Destinations?
    
    func navigateToA(via navigator: Navigator) {
        self.destination = .a {
            navigator.dismissAnyChildren()
        }
    }
}

You might look into Checkpoints as an alternative return mechanism.