从表单选择器中选择 CoreData 实体

Question

我有以下代码：

import SwiftUI

struct LearnView: View {
    
    @State private var selectedLanguage: Language?
    @State private var selectedCategory: SubCategory?
    @State private var selectedDate = Date()
     
    @Environment(\.managedObjectContext) private var viewContext
    @FetchRequest(entity: Language.entity(), sortDescriptors: []) var languages: FetchedResults<Language>
    @FetchRequest(entity: SubCategory.entity(), sortDescriptors: []) var subCategories: FetchedResults<SubCategory>
    
    var body: some View {
        NavigationView {
            ZStack {
                Form {
                    Section("Learning Schedule") {
                        Picker("Please choose a language", selection: $selectedLanguage) {
                            ForEach(languages, id: \.self) {
                                Text([=10=].name ?? "Unknown")
                            }
                        }
                        Text("You selected: \(selectedLanguage?.name ?? "Unknown")")
                    }
                }
            }
        }
    }
}

我可以点击表单行，然后会看到来自 CoreData 'languages' 实体的语言列表。但是，当我在导航到的视图中的选择器中点击一种语言时，它不会根据我的选择在它上面放置一个复选标记，并且 return 到表单屏幕。它只是在“您选择的：”文本字段中显示“未知”。

语言和子类别实体：

Answer 1

正如所写，您没有匹配选择器和 FetchResult 的数组类型。看评论

import SwiftUI

@available(iOS 15.0, *)
struct LearnView: View {
    //This is optional Language
    @State private var selectedLanguage: Language?
    //I commented out variables that are not part of the reproducible body provided
    //@State private var selectedCategory: SubCategory?
    //@State private var selectedDate = Date()
    
    @Environment(\.managedObjectContext) private var viewContext
     //This is FetchedResults<Language>
    @FetchRequest(entity: Language.entity(), sortDescriptors: []) var languages: FetchedResults<Language>
    // @FetchRequest(entity: SubCategory.entity(), sortDescriptors: []) var subCategories: FetchedResults<SubCategory>
    
    var body: some View {
        NavigationView {
            ZStack {
                Form {
                    Section("Learning Schedule") {
                        Picker("Please choose a language", selection: $selectedLanguage) {
                            //Map is needed for a plain array of languages
                            //ForEach(languages.map{[=10=]}, id: \.self) { language in
                            //This version works too
                            //The point is to go from FetchedResults<Language> to [Language]
                            ForEach(Array(languages), id: \.self) { language in
                                
                                Text(language.name ?? "Unknown")
                                //The casting is necessary to make it an optional since your @State is an optional
                                    .tag(language as? Language)
                            }
                        }
                        Text("You selected: \(selectedLanguage?.name ?? "Unknown")")
                    }
                }
            }
        }
    }
}

@available(iOS 15.0, *)
struct LearnView_Previews: PreviewProvider {
    static var previews: some View {
        LearnView().environment(\.managedObjectContext, PersistenceController.preview.container.viewContext)
    }
}

从表单选择器中选择 CoreData 实体

Choosing CoreData Entities from form picker

core-data

picker

swift

swiftui