NavigationSplitView does not run .task for each detail view instance

I should also clarify: I'm running this on macOS.

I just tested; it reproduces on iPad. However it works fine on iPhone.

Looks like this is related: https://stackoverflow.com/questions/73267638/how-to-run-task-or-onappear-on-navigationsplitview-detail-for-every-selectio

I re-watched the Demystifying SwiftUI and Data Essentials in SwiftUI WWDC sessions. I basically learned that the LoadingState I have above needs to be "extracted" from CategoryDetail and maintained in the CategoryNavigation*View as a [Category:LoadingState] dictionary. This way the state is persisted and associated with the Category.

I also used the modifier .task(id:) so that it would execute when the selection changed. It's also still tricky to understand the best way to show "this hasn't ever started loading yet".

enum Category: CaseIterable, Hashable, Identifiable {
  case first
  case second
  var id: Self {
    self
  }
}

struct CategoryRow: View {
  let category: Category

  var body: some View {
    Text("Row: \(String(describing: category))")
  }
}

extension Binding {
  public func defaultValue<T>(_ value: T) -> Binding<T> where Value == T? {
    Binding<T> {
      wrappedValue ?? value
    } set: {
      wrappedValue = $0
    }
  }
}

struct CategoryDetail: View {
  enum LoadingState {
    case none
    case loading
    case loaded
    case error
  }

  @Binding var category: Category?
  @Binding var loadingState: LoadingState

  var body: some View {
    Group {
      if category == nil {
        Text("Select A Category")
      } else {
        VStack {
          Text("Category: \(String(describing: category))")
          Text("LoadingState: \(String(describing: loadingState))")
        }
      }
    }.task(id: category) {
      guard let category else {
        debugPrint("nothing selected")
        return
      }

      guard loadingState == CategoryDetail.LoadingState.none else {
        debugPrint("Early Exit \(String(describing: category)): \(String(describing: loadingState))")
        return
      }

      loadingState = .loading
      do {
        try await Task.sleep(for: .seconds(2))
        loadingState = .loaded
      } catch {
        loadingState = .error
      }
    }
  }
}

struct CategoryNavigationSplitView: View {
  @State var selectedCategory: Category?
  @State var loadingStates : [Category : CategoryDetail.LoadingState] = [:]


  var body: some View {
    NavigationSplitView {
      List(Category.allCases, selection: $selectedCategory) { category in
        NavigationLink(value: category) { CategoryRow(category: category) }
      }
    } detail: {
      CategoryDetail(category: $selectedCategory,
                     loadingState: (selectedCategory != nil) ?
                            $loadingStates[selectedCategory!].defaultValue(.none) :
                      .constant(.none))
    }
  }
}

struct CategoryNavigationView: View {
  @State var selectedCategory: Category?
  @State var loadingStates : [Category : CategoryDetail.LoadingState] = [:]

  var body: some View {
    NavigationView {
      List(Category.allCases, selection: $selectedCategory) { category in
        NavigationLink {
          CategoryDetail(category: $selectedCategory,
                         loadingState: (selectedCategory != nil) ?
                                $loadingStates[selectedCategory!].defaultValue(.none) :
                          .constant(.none))
        } label: {
          CategoryRow(category: category)
        }
      }
    }

    Text("Select a Category")
  }
}