带有@EnvironmentObject 的导航栏项目

Question

I would like to create a Settings view using SwiftUI. I mainly took the official example from Apple about SwiftUI to realize my code. The settings view should have a toggle to whether display or not my favorites items.

For now I have a landmarks list and a settings view.

struct Landmark: Hashable, Codable, Identifiable {
    var id: Int
    var imageName: String
    var title: String
    var isFavorite: Bool
    var description: String

    enum CodingKeys: String, CodingKey {
        case id, imageName, title, description
    }
}

final class UserData: ObservableObject {
    @Published var showFavoriteOnly: Bool = false
    @Published var items: [Landmark] = landmarkData
    @Published var showProfile: Bool = false
}

struct ItemList: View {
    @EnvironmentObject var userData: UserData
    @State var trailing: Bool = false

    init() {
        UITableView.appearance().separatorStyle = .none
    }

    var body: some View {
        NavigationView {
            List {
                VStack {
                    CircleBadgeView(text: String(landmarkData.count), thickness: 2)
                    Text("Tutorials available")
                }.frame(minWidth:0, maxWidth: .infinity)

                ForEach(userData.items) { landmark in
                    if !self.userData.showFavoriteOnly || landmark.isFavorite {
                        ZStack {
                            Image(landmark.imageName)
                                .resizable()
                                .frame(minWidth: 0, maxWidth: .infinity)
                                .cornerRadius(10)
                                .overlay(ImageOverlay(text: landmark.title), alignment: .bottomTrailing)
                            Text(String(landmark.isFavorite))


                            NavigationLink(destination: TutorialDetailView(landmark: landmark)) {
                                EmptyView()
                            }.buttonStyle(PlainButtonStyle())
                        }
                    }
                }
            }.navigationBarTitle("Tutorials")
                .navigationBarItems(trailing: trailingItem())
        }
    }
}

extension ItemList {
    func trailingItem () -> some View {
        return HStack {

            if userData.showProfile {
                NavigationLink(destination: ProfileView()) {
                    Image(systemName: "person.circle")
                        .imageScale(.large)
                        .accessibility(label: Text("Profile"))
                }
            }

            NavigationLink(destination: SettingsView().environmentObject(userData)) {
                Image(systemName: "gear")
                    .imageScale(.large)
                    .accessibility(label: Text("Settings"))
            }
        }
    }
}

As you can see my SettingsView is accessible from navigationBarItems of my NavigationView. I don't know if it's the problem or not but when I put the Toggle inside the ListView it works as expected. But now when I trigger the toggle to enable only favorite my application crash instantly.

I've tried to trigger the Show profile toggle from SettingsView and it works.

struct SettingsView: View {
    @EnvironmentObject var userData: UserData

    var body: some View {
        Form {
            Section(header: Text("General")) {
                Toggle(isOn: $userData.showProfile) {
                    Text("Show profile")
                }
                Toggle(isOn: $userData.showFavoriteOnly) {
                    Text("Favorites only")
                }
            }

            Section(header: Text("UI")) {
                Toggle(isOn: .constant(false)) {
                    Text("Dark mode")
                }

                NavigationLink(destination: Text("third")) {
                    Text("Third navigation")
                }
            }

        }.navigationBarTitle(Text("Settings"), displayMode: .inline)
    }
}

In brief, the crash appears in my SettingsView when I trigger the Show only favorite Toggle and then I try to go back to the previous view which is ItemListView

The only information I can get about the error is Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

You can find the whole project on my GitHub : https://github.com/Hurobaki/swiftui-tutorial

Some help would be really appreciated :)

Answer 1

Here is a minimal version of your example code, that works:

struct Landmark: Hashable, Codable, Identifiable {
  var id: Int
  var imageName: String
  var title: String
  var isFavorite: Bool
  var description: String
}

final class UserData: ObservableObject {
  @Published var showFavoriteOnly: Bool = false
  @Published var items: [Landmark] = [
    Landmark(id: 1, imageName: "a", title: "a", isFavorite: true, description: "A"),
    Landmark(id: 2, imageName: "b", title: "b", isFavorite: false, description: "B")
  ]
}

struct ContentView: View {
  @EnvironmentObject var userData: UserData

  var body: some View {
    NavigationView {
      List(userData.items.filter { !userData.showFavoriteOnly || $0.isFavorite }) { landmark in
        Text(String(landmark.isFavorite))
      }
      .navigationBarTitle("Tutorials")
      .navigationBarItems(trailing: trailingItem())
    }
  }

  func trailingItem () -> some View {
    return HStack {
      NavigationLink(destination: SettingsView()) {
        Text("Settings")
      }
    }
  }
}

struct SettingsView: View {
  @EnvironmentObject var userData: UserData

  var body: some View {
    Form {
      Section(header: Text("General")) {
        Toggle(isOn: $userData.showFavoriteOnly) {
          Text("Favorites only")
        }
      }
    }.navigationBarTitle(Text("Settings"), displayMode: .inline)
  }
}