SwiftUI 从 CoreData 设置初始选择器值

Question

我正在绞尽脑汁地试图弄清楚如何让我的选择器显示已经存储的 CoreData 值。我希望它显示在选择器的右侧，就像用户刚刚选择它一样。我尝试self.updatedItemAttribute = self.editItem.attribute ?? ""在选择器之前添加以设置初始值，但这不会构建。@State我也尝试在(eg )中定义它，@State var updatedItemAttribute: String = self.editItem.attribute但这也不能构建。如果我在选择器之前添加 a TextField，它将设置该值，但我不希望有一个TextField带有该值的值只是为了让它设置。关于如何在选择器之前updatedItemAttribute进行设置有什么想法吗？editItem.attribute谢谢。

import CoreData
import SwiftUI

struct EditItemView: View {
    @Environment(\.managedObjectContext) var moc
    @Environment(\.presentationMode) var presentationMode
    @ObservedObject var editItem: Item

    @State var updatedItemName: String = ""
    @State var updatedItemAttribute: String = ""

    let attributes = ["Red", "Purple", "Yellow", "Gold"]

    var body: some View {
        NavigationView {
            Form {
                Section {
                    TextField("Name of item", text: $updatedItemName)
                        .onAppear {
                            self.updatedItemName = self.editItem.name ?? ""
                    }
                    Picker("Test attribute", selection: self.$updatedItemAttribute) {
                        ForEach(attributes, id: \.self) {
                            Text($0)
                                .onAppear {
                                    self.updatedItemAttribute = self.editItem.attribute ?? ""
                                }
                        }
                    }
                }
...

Answer 1

你必须在 init 中这样做，如下所示

struct EditItemView: View {
    @Environment(\.managedObjectContext) var moc
    @Environment(\.presentationMode) var presentationMode
    @ObservedObject var editItem: Item

    @State private var updatedItemName: String
    @State private var updatedItemAttribute: String

    init(editItem item: Item) {             // << updated here
        self.editItem = item
        self._updatedItemName = State<String>(initialValue: item.name ?? "")
        self._updatedItemAttribute = State<String>(initialValue: item.attribute ?? "")
    }

    let attributes = ["Red", "Purple", "Yellow", "Gold"]

    var body: some View {
        NavigationView {
            Form {
                Section {
                    TextField("Name of item", text: $updatedItemName)
                    Picker("Test attribute", selection: self.$updatedItemAttribute) {
                        ForEach(attributes, id: \.self) {
                            Text($0)
                        }
                    }
                }
            }
        }
    }
}