onAppear不允许保存/更新选择器值的更改？

问题描述

我正在构建一个Edit View，该视图允许用户对列表项进行更新并将其保存回核心数据和列表中。为此，我使用.onAppear操作在适当字段中从列表中传递值。

所有数据都会适当地传递，并且切换和文本字段使我可以轻松进行更改并将其保存回核心数据并更新列表项。但是，如果我尝试更改选择器值（emojiChoice）并选择一个新值，则选择器值不会更改或保存回Core Data。

当我注释掉选择器变量（emojiChoice）的onAppear操作时，选择器现在允许我选择所需的值并将其保存回Core Data。我还具有另一个视图，该视图允许用户创建与该“编辑视图”几乎相同的项目，但减去onAppear操作也可以正常工作。选择器允许用户选择表情符号。因为有很多表情符号，所以我创建了一个数组，而只是将所选表情符号的数组索引作为Int传递。

如何解决此问题，以允许选择器显示要编辑的值并允许对其进行更改？

这是“编辑视图”的代码：

struct editRemindr: View {
@Environment(\.managedObjectContext) var moc
@Environment(\.presentationMode) var presentationMode

let emojiList = EmojiList()
@ObservedObject var reminder: ReminderEntity
@State private var showingDeleteAlert = false

// Form Variables
@State var notifyOn = true
@State var emojiChoice = 0
@State var notification: String
@State var notes: String

// Delete Reminder Function
func deleteAction() {
    moc.delete(reminder)
    // try? self.moc.save()
    presentationMode.wrappedValue.dismiss()
}

// View Controller
var body: some View {
    Form {

        // On/Off Toggle
        Toggle(isOn: $notifyOn) {
            Text("On/Off")
        }

        // Emoji Picker
        Picker(selection: $emojiChoice,label: Text("Emoji")) {
            ForEach(0 ..< emojiList.emojis.count) {
                Text(self.emojiList.emojis[$0])
            }
        }

        // Notification Text
        Section(header: Text("NOTIFICATION")) {
            HStack {
                TextField("Write your notification...",text: $notification)
                    .onReceive(notification.publisher.collect()) {
                        self.notification = String($0.prefix(60)) // <---- SET CHARACTER LIMIT
                }
                Text("\(notification.count) / 60")
                    .font(.caption)
                    .foregroundColor(.gray)
            }
        }

        // Notes Text
        Section(header: Text("NOTES")) {
            VStack {
                MultiLineTextField(text: $notes).frame(numLines: 6)
                    .padding(.top,5)
                    .onReceive(notes.publisher.collect()) {
                        self.notes = String($0.prefix(240)) // <---- SET CHARACTER LIMIT
                }
                Text("\(notes.count) / 240")
                    .font(.caption)
                    .foregroundColor(.gray)
                    .frame(maxWidth: .infinity,alignment: .trailing)
            }
        }

        // Save Changes Button
        Section() {
            Button (action: {
                self.reminder.dateCreated = Date()
                self.reminder.notifyOn = self.notifyOn
                self.reminder.emojiChoice = Int64(self.emojiChoice)
                self.reminder.notification = self.notification
                self.reminder.notes = self.notes

                try? self.moc.save()

                self.presentationMode.wrappedValue.dismiss()
            }) {
                Text("SAVE CHANGES")
                    .fontWeight(.bold)
                    .foregroundColor(.white)
                    .font(.body)
            }        .padding()
                .frame(maxWidth: .infinity)
                .background(Color.green)
                .padding(.vertical,-6)
                .padding(.horizontal,-15)

            // Cancel Button
            Button(action: {
                self.presentationMode.wrappedValue.dismiss()
            }) {
                Text("Cancel")
                    .frame(maxWidth: .infinity)
            }
        }
    }

    // Make List Items Appear in Fields
    .onAppear(perform: {
        self.notifyOn = self.reminder.notifyOn
        self.emojiChoice = Int(self.reminder.emojiChoice)
        self.notification = self.reminder.notification ?? "unknown"
        self.notes = self.reminder.notes ?? "unknown"
    }) 
        .alert(isPresented: $showingDeleteAlert) {
            Alert(title: Text("Delete Reminder"),message: Text("Are you sure you want to delete this Reminder?"),primaryButton: .destructive(Text("Delete")) {
                self.deleteAction()
                },secondaryButton: .cancel()
            )
    }
    .navigationBarTitle("Edit Reminder")
    .navigationBarItems(trailing: Button(action: {self.showingDeleteAlert = true
    }) {
        Image(systemName: "trash")

    })
} 

// Creates Text Limits
class TextLimit: ObservableObject {
    @Published var text = "" {
        didSet {
            if text.count > characterLimit && oldValue.count <= characterLimit {
                text = oldValue
            }
        }
    }
    let characterLimit: Int

    init(limit: Int = 5){
        characterLimit = limit
    }

}

如果有帮助，这是带有列表的内容视图的代码。

struct ContentView: View {

@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: ReminderEntity.entity(),sortDescriptors: [NSSortDescriptor(keyPath: \ReminderEntity.dateCreated,ascending: false)])
var reminder: FetchedResults<ReminderEntity>

@State private var showingAddScreen = false
@State var showWelcomeScreen = false

let emojiList = EmojiList()

//Toggle Control
@State var notifyOn = true

// Save Items Function
func saveItems() {
    do {
        try moc.save()
    } catch {
        print(error)
    }
}

// Delete Item Function
func deleteItem(indexSet: IndexSet) {
    let source = indexSet.first!
    let listItem = reminder[source]
    moc.delete(listItem)
}

// View Controller
var body: some View {
    VStack {
        NavigationView {
            ZStack (alignment: .top) {

                // List View
                List {
                    ForEach(reminder,id: \.self) { notification in
                        NavigationLink(destination: editRemindr(reminder: notification,notification: notification.notification ?? "unknown",notes: notification.notes ?? "unknown")) {
                            // Text within List View
                            HStack {
                                // MARK: TODO
                                // Toggle("NotifyOn",isOn: true)
                                // .labelsHidden() // Hides the label/title
                                Text("\(self.emojiList.emojis[Int(notification.emojiChoice)]) \(notification.notification!)")
                            } 
                        }
                    } 
                    .onDelete(perform: deleteItem)
                }

                    // Navigation Items
                    .navigationBarTitle("",displayMode: .inline)
                    .navigationBarItems(
                        leading:
                        HStack {

                            Button(action: {
                                self.showWelcomeScreen.toggle()
                            }) {
                                Image(systemName: "info.circle.fill")
                                    .font(.system(size: 24,weight: .regular))
                            }.foregroundColor(.gray)

                            // Positioning Remindr Logo on Navigation
                            Image("remindrLogoSmall")
                                .resizable()
                                .aspectRatio(contentMode: .fit)
                                //.frame(width: 60,height: 60,alignment: .center)
                                .padding(.leading,83)
                                .padding(.top,-10)
                        },// Global Settings Navigation Item
                        trailing: NavigationLink(destination: globalSettings()){
                            Image("settings")
                                .font(Font.title.weight(.ultraLight))
                        }.foregroundColor(.gray)
                )

                // Add New Reminder Button
                VStack {
                    Spacer()
                    Button(action: { self.showingAddScreen.toggle()
                    }) {
                        Image("addButton")
                            .renderingMode(.original)
                    }
                    .sheet(isPresented: $showingAddScreen) {

                        newRemindr().environment(\.managedObjectContext,self.moc)

                    } 
                }
            }
        }  .sheet(isPresented: $showWelcomeScreen) {
            welcomeScreen()
        }
    }
}

解决方法

尝试以下

    // Emoji Picker
    Picker(selection: $emojiChoice,label: Text("Emoji")) {
        ForEach(0 ..< emojiList.emojis.count,id: \.self) { // << added id !!
            Text(self.emojiList.emojis[$0])
        }
    }

,

我为选择器值创建了一个自定义绑定，它似乎可以解决问题。感谢Reddit user End3r117为我指出正确的方向！

// View Controller
var body: some View {
    
    let reminderChoice = Binding(
        get: { Int(self.reminder.emojiChoice) },set: { self.reminder.emojiChoice = Int64($0) }
    )
    return
        Form {
            
            // On/Off Toggle
            Toggle(isOn: $notifyOn) {
                Text("On/Off")
            }

            // Emoji Picker
            Picker(selection: reminderChoice,label: Text("Emoji")) {
                ForEach(0 ..< self.emojiList.emojis.count,id: \.self) {
                    Text(self.emojiList.emojis[$0])
                }
            }