SwiftUI macOS NavigationView - onChange(of: Bool) action tried to update multiple times per frame-CodePudding

I'm seeing onChange(of: Bool) action tried to update multiple times per frame warnings when clicking on NavigationLinks in the sidebar for a SwiftUI macOS App.

Here's what I currently have:

import SwiftUI

@main
struct BazbarApp: App {

    @StateObject private var modelData = ModelData()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(modelData)
        }
    }
}


class ModelData: ObservableObject {
    @Published var myLinks = [URL(string: "https://google.com")!, URL(string: "https://apple.com")!, URL(string: "https://amazon.com")!]
}

struct ContentView: View {

    @EnvironmentObject var modelData: ModelData

    @State private var selected: URL?

    var body: some View {
        NavigationView {

            List(selection: $selected) {
                Section(header: Text("Bookmarks")) {

                    ForEach(modelData.myLinks, id: \.self) { url in
                        NavigationLink(destination: DetailView(selected: $selected) ) {
                            Text(url.absoluteString)
                        }
                        .tag(url)
                    }

                }
            }
            .onDeleteCommand {
                if let selected = selected {
                    modelData.myLinks.remove(at: modelData.myLinks.firstIndex(of: selected)!)
                }

                selected = nil
            }

            Text("Choose a link")
        }
    }
}

struct DetailView: View {
    @Binding var selected: URL?

    var body: some View {

        if let selected = selected {
            Text("Currently selected: \(selected)")
        }
        else {
            Text("Choose a link")
        }
    }
}

When I alternate clicking on the second and third links in the sidebar, I eventually start seeing the aforementioned warnings in my console.

Here's a gif of what I'm referring to:

Interestingly, the warning does not appear when alternating clicks between the first and second link.

Does anyone know how to fix this?

I'm using macOS 12.2.1 & Xcode 13.2.1.

Thanks in advance

CodePudding user response：

I think the issue is that both the List(selection:) and the NavigationLink are trying to update the state variable selected at once. A List(selection:) and a NavigationLink can both handle the task of navigation. The solution is to abandon one of them. You can use either to handle navigation.

Since List look good, I suggest sticking with that. The NavigationLink can then be removed. The second view under NavigationView is displayed on the right, so why not use DetailView(selected:) there. You already made the selected parameter a binding variable, so the view will update if that var changes.

struct ContentView: View {
    
    @EnvironmentObject var modelData: ModelData
    
    @State private var selected: URL?
    
    var body: some View {
        NavigationView {
            
            List(selection: $selected) {
                Section(header: Text("Bookmarks")) {
                    
                    ForEach(modelData.myLinks, id: \.self) { url in
                        Text(url.absoluteString)
                            .tag(url)
                    }
                    
                }
            }
            .onDeleteCommand {
                if let selected = selected {
                    modelData.myLinks.remove(at: modelData.myLinks.firstIndex(of: selected)!)
                }
                
                selected = nil
            }
            
            DetailView(selected: $selected)
        }
    }
}