SwiftUI AppStorage，UserDefaults和ObservableObject

Question

我有两个不同的观点，ContentView和CreateView。在CreateView中，我通过textfield获取用户的输入，一旦用户单击Save按钮，输入将存储在AppStorage中。然后，我想在ContentView上显示保存的输入。在这里，我尝试使用State & Binding，但效果不太好。如何在CreateView中使用在ContentView中创建的变量？我应该使用什么财产..。

谢谢

这是最新的问题和代码..。

struct ContentView: View {
    // MARK: - PROPERTY
    @ObservedObject var appData: AppData
    let createpage = CreatePage(appData: AppData())
    
    var body: some View {
        HStack {
            NavigationLink("+ create a shortcut", destination: CreatePage(appData: AppData()))
                .padding()
            Spacer()
        } //: HStack - link to creat page
        VStack {
            Text("\(appData.shortcutTitle) - \(appData.shortcutOption)")
        }
        
    }
    
    struct CreatePage: View {
        // MARK: - PROPERTY
        @AppStorage("title") var currentShortcutTitle: String?
        @AppStorage("option") var currentOption: String?
        @Environment(\.presentationMode) var presentationMode
        @ObservedObject var appData: AppData
        
        var body: some View {
            NavigationView{
                ScrollView{
                    Text("Create a ShortCut")
                        .padding()
                    
                    HStack {
                        TextField("what is the title?", text: $appData.titleInput)
                            .textFieldStyle(RoundedBorderTextFieldStyle())
                            //.frame(width: 150, height: 60, alignment: .center)
                            .border(Color.black)
                            .padding()
                    } //: HStack - Textfield - title
                    .padding()
                    
                    HStack (spacing: 10) {
                        TextField("options?", text: $appData.optionInput)
                            .textFieldStyle(RoundedBorderTextFieldStyle())
                            .frame(width: 80, height: 40, alignment: .leading)
                            .padding()
                    } //: HStack - Textfield - option
                    .padding()
                    
                    Button(action: {
                        self.appData.shortcutTitle = self.appData.titleInput
                        self.appData.shortcutOption = self.appData.optionInput
                        UserDefaults.standard.set(appData.shortcutTitle, forKey: "title")
                        UserDefaults.standard.set(appData.shortcutOption, forKey: "option")
                        presentationMode.wrappedValue.dismiss()
                    }, label: {
                        Text("Save")
                            .padding()
                            .frame(width: 120, height: 80)
                            .border(Color.black)
                    }) //: Button - save
                    .padding(.top, 150)
                } //: Scroll View
            } //: Navigation View
        } //: Body
        
        class AppData: ObservableObject {
            @Published var shortcutTitle : String = "Deafult Shortcut"
            @Published var shortcutOption : String = "Default Option"
            @Published var titleInput : String = ""
            @Published var optionInput : String = ""
        }

所以问题是

当我在

1. 上放置新输入并在CreatePage按钮上设置选项时，新输入不会出现在ContentView page.The output上，它会继续显示标题和选项的默认值，而不会显示用户输入。如果用户输入了新的输入并点击了保存按钮，我希望将它们存储在AppStorage中，并希望将数据保存在ContentView上(还没有创建UI )。我在正确的方向上使用AppStorage和UserDefaults吗？

如果有人对这些问题有洞察力..。愿意接受你的建议或推荐信。

Answer 1

您正在多个地方创建AppData实例。为了共享数据，您必须共享AppData的一个实例。

我假定您在ContentView的父视图中创建了@ObservedObject var appData: AppData，因为您在视图的顶部定义了@ObservedObject var appData: AppData(没有= AppData())。这可能在您的WindowGroup中，您还必须有一个NavigationView。

我删除了next (let createpage = CreatePage(appData: AppData()))，因为它什么也不做。在NavigationLink中，我传递了相同的AppData实例。

struct ContentView: View {
    // MARK: - PROPERTY
    @StateObject var appData: AppData = AppData() //Don't need to have `= AppData()` if you already create it in a parent view
    
    var body: some View {
        // I'm assuming there's a NavigationView in a parent view
        VStack { //note that I've wrapped the whole view in a VStack to avoid having two root nodes (which can perform differently in NavigationView depending on the platform)
            HStack {
                NavigationLink("+ create a shortcut", destination: CreatePage(appData: appData))
                    .padding()
                Spacer()
            } //: HStack - link to creat page
            VStack {
                Text("\(appData.shortcutTitle) - \(appData.shortcutOption)")
            }
        }
    }
}

struct CreatePage: View {
    // MARK: - PROPERTY
    @AppStorage("title") var currentShortcutTitle: String?
    @AppStorage("option") var currentOption: String?
    @Environment(\.presentationMode) var presentationMode
    @ObservedObject var appData: AppData
    
    var body: some View {
        NavigationView{
            ScrollView{
                Text("Create a ShortCut")
                    .padding()
                
                HStack {
                    TextField("what is the title?", text: $appData.titleInput)
                        .textFieldStyle(RoundedBorderTextFieldStyle())
                        //.frame(width: 150, height: 60, alignment: .center)
                        .border(Color.black)
                        .padding()
                } //: HStack - Textfield - title
                .padding()
                
                HStack (spacing: 10) {
                    TextField("options?", text: $appData.optionInput)
                        .textFieldStyle(RoundedBorderTextFieldStyle())
                        .frame(width: 80, height: 40, alignment: .leading)
                        .padding()
                } //: HStack - Textfield - option
                .padding()
                
                Button(action: {
                    appData.shortcutTitle = appData.titleInput
                    appData.shortcutOption = appData.optionInput
                    presentationMode.wrappedValue.dismiss()
                }, label: {
                    Text("Save")
                        .padding()
                        .frame(width: 120, height: 80)
                        .border(Color.black)
                }) //: Button - save
                .padding(.top, 150)
            } //: Scroll View
        } //: Navigation View
    } //: Body
}

关于@AppStorage和UserDefaults，现在很难用它们来判断您的意图。但是，您不需要声明AppStorage并以相同的键调用UserDefaults -- @AppStorage为您写UserDefaults。在https://www.hackingwithswift.com/quick-start/swiftui/what-is-the-appstorage-property-wrapper阅读更多内容

Answer 2

您可以使用符合NSObject的单例NSObject，这样就可以观察任何东西，甚至是更老的苹果对象，比如进度。

class appData : NSObject , ObservableObject {
    static let shared = appData()
    @Published var localItems = Array<AVPlayerItem>()
    @Published var fractionCompleted : Double = 0
    @Published var downloaded : Bool = false
    @Published var langdentifier = UserDefaults.standard.value(forKey: "lang") as? String ?? "en" {
        didSet {
            print("AppState isLoggedIn: \(langIdentifier)")
        }
    }
    var progress : Progress?
    override init() {
    }
}

然后您可以在代码中的任何地方使用它，如下所示：

appData.shared.langIdentifier == "en" ? .leading : .trailing