SwiftUI 嵌套 ForEach 应该只用于 *constant* 数据

Posted 2023-03-11

【中文标题】SwiftUI 嵌套 ForEach 应该只用于 *constant* 数据

【英文标题】：SwiftUI Nested ForEach should only be used for *constant* data

【发布时间】：2020-05-13 21:19:02

【问题描述】：

我创建了一个带有嵌套 ForEach 循环的视图，我在日志中收到以下错误：

> count (2) != its initial count (1). `ForEach(_:content:)` should only
> be used for *constant* data. Instead conform data to `Identifiable` or
> use `ForEach(_:id:content:)` and provide an explicit `id`!

我已经使结构符合可识别的，这似乎无法解决错误。

我该如何解决这个错误？

import SwiftUI

struct LessonStruct: Identifiable 
    var id: Int
    var name: String
    var questions: [QuestionStruct]


struct QuestionStruct: Identifiable 
    var id: Int
    var type: QuestionType
    var description: String
    var questionId: Int


class LessonsObject: ObservableObject 
    @Published var Array = [LessonStruct]()
    @Published var selectedLesson: Int?


struct CreateLessonList: View 

    @EnvironmentObject var lesson: LessonsObject
    @Binding var showingActionSheet: Bool

    var rowNumber:Int = 0

    var body: some View 


        VStack


            ForEach(self.lesson.Array)  each in

                VStack(spacing: 0)

                    HStack()

                        TextField("Lesson \(each.id) - click to change name", text: self.$lesson.Array[each.id-1].name).font(.custom("Proxima Nova Alt Bold", size: 20)).foregroundColor(Color.white).padding(.leading, 10)

                        Spacer()
                        Image("PlusIcon").resizable().frame(width: 20, height: 20).padding(.trailing, 10).onTapGesture 
                            self.lesson.selectedLesson = each.id - 1
                            self.showingActionSheet = true
                        

                    .frame( height: 40).background(Color.init("Orange"))


                    if(self.lesson.Array[each.id - 1].questions.count == 0)
                    VStack
                        Text("Click the '+' icon to add a question.").font(.custom("Proxima Nova Alt Thin", size: 15))
                    .frame(height: 70)
                    else


                        ForEach(self.lesson.Array[each.id - 1].questions.indices) i in

                            if(self.lesson.Array[each.id - 1].questions[i].type == .Translation)
                                Group
                                HStack
                                    Image("TranslationIcon").resizable().frame(width: 50, height:65)
                                    Text(self.lesson.Array[each.id - 1].questions[i].description)
                                    Spacer()
                                .padding(20)
                                
                            

                        

                    

                
            .background(Color.init("White"))
        
      
    

【参考方案1】：

使用内部 ForEach 如下

ForEach(self.lesson.Array[each.id - 1].questions) question in

    if(question.type == .Translation)
        Group
        HStack
            Image("TranslationIcon").resizable().frame(width: 50, height:65)
            Text(question.description)
            Spacer()
        .padding(20)
        
    

并检查您的 LessonStruct.id 构造逻辑，因为引用 [.id - 1] 看起来容易出错。