SwiftUI，“致命错误：在展开可选值时意外发现 nil”消息

Question

我运行代码，然后收到以下错误消息： 致命错误：在展开可选值时意外发现 nil

1. AppData 文件

struct Shortcut {
    var title: String
    var option: String
}

struct ShortcutViewModel: Identifiable {
    var id = UUID()
    var shortcut: Shortcut
    
    var title: String {
        return shortcut.title.capitalized
    }
    
    var option: String {
        return shortcut.option
    }
}

class AppData: ObservableObject {
    @Published var userData: [ShortcutViewModel]
    
    @Published var showTitle: String {
        didSet {
            UserDefaults.standard.set(showTitle, forKey: "TitleInput")
        }
    }
    
    @Published var showOption: String {
        didSet {
            UserDefaults.standard.set(showOption, forKey: "OptionInput")
        }
    }
    
    init() {
        userData = [
            ShortcutViewModel(shortcut: Shortcut(title: "What for Dinner?", option: "Chinese")),
            ShortcutViewModel(shortcut: Shortcut(title: "What for Lunch?", option: "Pasta")),
            ShortcutViewModel(shortcut: Shortcut(title: "What for Breakfast?", option: "Toast"))
        ]
        self.showTitle = UserDefaults.standard.string(forKey: "TitleInput")!   // *here I get Fatal Error msg*
        self.showOption = UserDefaults.standard.string(forKey: "OptionInput")!
    }
}

1. ContentView 文件

struct ContentView: View {
    // MARK: - PROPERTY
    let createpage = CreateView()
    // MARK: - BODY
    var body: some View {
        ZStack {
            VStack {
                NavigationBarView()
                NavigationView{
                    ScrollView{
                        HStack {
                            NavigationLink("+ create a shortcut", destination: CreateView())
                                .font(.title3)
                                .foregroundColor(.blue)
                                .padding()
                                .frame(width: 200, height: 60)
                                .background(
                                RoundedRectangle(cornerRadius: 10,
                                                 style: .continuous)
                                    .fill(
                                        Color(red:0.2, green: 0.45, blue: 1.0, opacity: 0.3)))
                                    
                            Spacer()
                        } //: HStack - link to create page
                        //.frame(minWidth: 0, maxWidth: .infinity, maxHeight: 120)
                        .padding()
                    } //: ScrollView
                    
                    .navigationTitle("All Shortcuts")
                    
                } //: NavigationView
            
            } //: VStack
            .ignoresSafeArea(.all, edges: .all)
        } //: ZStack
        .ignoresSafeArea(.all, edges: .top)
    } //: var Body
}



// MARK: - PREVIEW
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView(text: .constant(""))
        
    }
}

1. 创建视图

struct CreateView: View {
    // MARK: - PROPERTY
    @Environment(\.presentationMode) var presentationMode
    @EnvironmentObject var appData: AppData
    @State var titleInput2 = ""
    @State var optionInput2 = ""
    
    // MARK: - BODY
    var body: some View {
        ZStack {
            VStack {
                NavigationView{
                    ScrollView{
                        HStack {
                            TextField("what is the title?", text: $titleInput2)
                                .font(.title2)
                                .foregroundColor(.white)
                                .padding()
                                .frame(width: 320, height: 80)
                                .background(
                                    RoundedRectangle(
                                        cornerRadius: 20,
                                        style: .continuous)
                                        .fill(
                                            Color(red:0.2, green: 0.45, blue: 1.0, opacity: 0.3)))
                                .padding()
                        } //: HStack - Textfield - title
                        .padding()
                        
                        HStack (spacing: 10) {
                            TextField("options", text: $optionInput2)
                                .font(.body)
                                .foregroundColor(.white)
                                .padding()
                                .frame(width: 120, height: 60, alignment: .leading)
                                .background(
                                    RoundedRectangle(
                                        cornerRadius: 10,
                                        style: .continuous)
                                        .fill(
                                            Color(red: 1.0, green: 0.2, blue: 0.2, opacity: 0.3)))
                                .padding()
                        } //: HStack - Textfield - option
                        .padding()
                        
                        Button(action: {
                            self.appData.showTitle = titleInput2 
                            self.appData.showOption = optionInput2
                            presentationMode.wrappedValue.dismiss()
                        }, label: {
                            Text("Save")
                                .padding()
                                .background(
                                    Circle()
                                        .fill(
                                            Color(red: 0.25, green: 0.1, blue: 0.6, opacity: 0.25))
                                        .frame(width: 120, height: 120))
                                
                        }) //: Button - save
                        .padding(.top, 150)
                    } //: Scroll View
                    .navigationTitle("Create a Shortcut")
                }//: Navigation View
            } //: VStack
            .ignoresSafeArea(.all, edges: .all)
        } //: ZStack
        .ignoresSafeArea(.all, edges: .all)
    } //: Body
}

struct CreateView_Previews: PreviewProvider {
    static var previews: some View {
        CreateView().environmentObject(AppData())
    }
}

4. 应用文件

@main  // *here I get Fatal Error msg*
struct WFT_demo2App: App {
    var body: some Scene {
        WindowGroup {    // *here I get Fatal Error msg*
            ContentView(text: .constant(""))
                .environmentObject(AppData())    // *here I get Fatal Error msg*
        }
    }
}

当我运行代码时（当我模拟它时），我在上面标记的几行中收到相同的致命错误消息。我想我错过了一些重要的东西。另外，在 3. CreateView 文件中，可以使用 @State var titleInput2 = "" 和 @State var optionInput2 = "" 吗？ 谢谢你的建议！

Answer 1

删除以下行，它不是要创建视图的地方，而是您在不注入环境对象的情况下创建它的地方：

struct ContentView: View {
    // MARK: - PROPERTY
    let createpage = CreateView()    // << this one !!

...

Answer 2

如果您要通过environmentObject 传递数据，那么您需要接收页面上的数据。您正在发送它但没有收到它。如果您想收到它，请在您的视图中将其添加到您的 body 上方。

@EnvironmentObject var appData: AppData

另外你使用NavigationView 错误，应该只有一个导航栏所以删除那些其他导航栏并将此代码用于你的App.swift

 @main  // *here I get Fatal Error msg*
struct WFT_demo2App: App {
    var body: some Scene {
        WindowGroup {    // *here I get Fatal Error msg*
         NavigationView {
            ContentView(text: .constant(""))
         }
                .environmentObject(AppData())    // *here I get Fatal Error msg*
        }
    }
}

再次：删除除此代码 sn-p 中的导航栏以外的所有其他导航栏。而且您必须使用此方法传递一次数据。但是注意您仍然需要在依赖其数据的每个视图上声明 `@EnvironmentObject var appData: AppData