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Question

总的来说，我对快速编程相当陌生，但我正在尝试构建一个有效的小测验视图，该视图接受JSON文件中的问答问题，并使用自定义的“应答”视图将它们以LazyVGrid模式显示在屏幕上。

这是我的自定义答案视图(很抱歉，测试在所有这些名称上，我有重复的文件来尝试不同的事情而不干扰我的原始文件！)：

struct TestAnswerTest: View {
    @State var answer: String
    @State private var selected = false
    var correctAnswers: [String]

    var body: some View {
        Text(answer)
            .font(.title)
            .bold()
            .frame(width: 165, height: 140)
            .contentShape(RoundedRectangle(cornerRadius: 25))
            .onTapGesture {
                self.selected.toggle()
            }
    }
}

我的问题结构：

struct Question2: Codable, Identifiable {
    let id: Int
    let category: String
    let question: String
    let answers: [String]
    let correctAnswers: [String]
    let options: Int
}

我的json数据样本供参考：

{
    "id": 1,
    "category": "staff",
    "question": "What are the 2 common names for the lines and spaces on sheet music?\n(Select 2 answers)",
    "answers": ["Staff", "Stave", "String", "Stem", "Stake", "Store"],
    "correctAnswers": ["Staff", "Stave"],
    "options": 6
}

这是我的小测验显示视图：

struct StaffRecap2: View {
    @State private var questionNumber = 0
    private let twoColumnGrid = [GridItem(.flexible()), GridItem(.flexible())]
    let questions:[Question2] = Bundle.main.decode("questions.json")
    
    var body: some View {
        let staffQuestions = questions.filter { $0.category.elementsEqual("staff")}
        
        NavigationView {
            VStack{
                Text(staffQuestions[questionNumber].question)
                
                LazyVGrid(columns: twoColumnGrid) {
                    ForEach(0..<staffQuestions[questionNumber].options, id:\.self) { number in
                        TestAnswerTest(answer: staffQuestions[questionNumber].answers[number],
                                       correctAnswers: staffQuestions[questionNumber].correctAnswers)
                    }
                    .toolbar {
                        ToolbarItemGroup(placement: .bottomBar) {
                            Button {
                                questionNumber += 1
                                print(staffQuestions[questionNumber])
                            } label: {
                                Text("Next Question")
                            }
                            .disabled(questionNumber == staffQuestions.count)
                        }
                    }
                }
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .background(Gradient(colors: [.teal, .blue]))
            .navigationTitle("Staff Recap")
            .navigationBarTitleDisplayMode(.inline)
            .toolbarBackground(.orange, for: .navigationBar)
            .toolbarBackground(.visible, for: .navigationBar)
        }
    }
}

我的问题是，如果我手动更改"questionNumber“属性和模拟器中的代码构建，并预览所有正确的详细信息，一切似乎都正常，但是如果我使用按钮转到下一个问题，它就会正确地更改问题，但不会更新新的答案选项的任何答案视图。我真的不明白为什么我在应答视图中使用correctAnswers修饰符打印onTapGesture数组，它也为这个问题打印正确的数组，并在我按下按钮时正确地更改。

我有点困惑，我相信这可能是很简单的事情，我错过了，但我陷入了僵局，希望能为我做错的事情找到正确方向的帮助或指点。

提前感谢！

Answer 1

下面是我在评论中提到的方法的一个非常基本的例子，即使用ObservableObject视图模型，在这里执行所有的数据处理。注意，我更新了Question模型和相关的json数据。

import Foundation
import SwiftUI


class QuestionModel: ObservableObject {
    
    @Published var questions:[Question] = []
    
    init() {
        if let loaded: [Question] = Bundle.main.decode("questions.json") {
            questions = loaded
        }
    }
    
    func addAnswer(to n: Int, answer: Answer) {
        questions[n].answers.append(answer)
    }
    
    func removeAnswer(from n: Int, answer: Answer) {
        questions[n].answers.removeAll(where: {$0.id == answer.id})
    }
    
    func isCorrectAnswer(_ n: Int) -> Bool {
        let arr1 = questions[n].correctAnswers.map{$0.id}
        let arr2 = questions[n].answers.map{$0.id}
        let theSet = Set(arr2).subtracting(arr1)
        return theSet.count == 0 && questions[n].correctAnswers.count == questions[n].answers.count
    }
    
}

struct Question: Codable, Identifiable {
    let id: Int
    var category: String
    let question: String
    var answers: [Answer] // <-- the answers from the user
    var possibles: [Answer] // <-- the possible choices of answers
    var correctAnswers: [Answer] // <-- just the correct answers
}

struct Answer: Codable, Identifiable, Hashable {
    let id: Int
    var answer: String
    var isCorrect: Bool
    var answered: Bool
}

struct ContentView: View {
    @StateObject var model = QuestionModel()
    
    @State private var questionNumber = 0
    @State private var showAnswer = false
    private let twoColumnGrid = [GridItem(.flexible()), GridItem(.flexible())]
    
    var body: some View {
        NavigationView {
            ScrollView {
                Text(model.questions[questionNumber].question)
                LazyVGrid(columns: twoColumnGrid) {
                    ForEach($model.questions[questionNumber].possibles) { $answer in
                        AnswerView(questionNumber: $questionNumber, answer: $answer)
                    }
                }
                NavigationLink("", destination: AnswerInfo(questionNumber: questionNumber), isActive: $showAnswer)
            }
            .toolbar {
                ToolbarItemGroup(placement: .bottomBar) {
                    Button {
                        if questionNumber + 1 < model.questions.count {
                            questionNumber += 1
                        }
                    } label: {
                        Text("Next Question").foregroundColor(.black)
                    }
                    Button {
                        showAnswer = true
                    } label: {
                        Text("Check answer").foregroundColor(.black)
                    }
                }
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .background(Gradient(colors: [.teal, .blue]))
        }
        .environmentObject(model)
        .navigationViewStyle(.stack)
        .navigationTitle("Staff Recap")
        .navigationBarTitleDisplayMode(.inline)
    }
}

struct AnswerInfo: View {
    @EnvironmentObject var model: QuestionModel
    @State var questionNumber: Int
    
    var body: some View {
        VStack {
            if model.isCorrectAnswer(questionNumber) {
                Text("Correct answer").font(.title)
            } else {
                Text("NOT correct answer").font(.title)
            }
            ForEach(model.questions[questionNumber].answers) { answer in
                Text(answer.answer)
            }
        }
    }
}

struct AnswerView: View {
    @EnvironmentObject var model: QuestionModel
    
    @Binding var questionNumber: Int
    @Binding var answer: Answer
    
    var body: some View {
        Button {
            answer.answered.toggle()
            if answer.answered {
                model.addAnswer(to: questionNumber, answer: answer)
            } else {
                model.removeAnswer(from: questionNumber, answer: answer)
            }
        } label: {
            Text(answer.answer)
                .font(.title)
                .bold()
                .frame(width: 165, height: 140)
                .contentShape(RoundedRectangle(cornerRadius: 25))
                .foregroundColor(answer.answered ? Color.red : Color.green)
        }
        .buttonStyle(.bordered)
    }
}

extension Bundle {
    func decode<T: Decodable>(_ file: String) -> T? {
        if let url = self.url(forResource: file, withExtension: nil) {
            do {
                let data = try Data(contentsOf: url)
                return try JSONDecoder().decode(T.self, from: data)
            } catch {
                print(error)
            }
        }
        return nil
    }
}

questions.json文件中的json数据

 [
     {
         "id": 1,
         "category": "staff",
         "question": "What are the 2 common names for the lines and spaces on sheet music?\n(Select 2 answers)",
         "answers": [],
         "possibles": [
             {"id": 1, "answer": "Staff", "isCorrect": false, "answered": false},
             {"id": 2, "answer": "Stave", "isCorrect": false, "answered": false},
             {"id": 3, "answer": "String", "isCorrect": false, "answered": false},
             {"id": 4, "answer": "Stem", "isCorrect": false, "answered": false},
             {"id": 5, "answer": "Stake", "isCorrect": false, "answered": false},
             {"id": 6, "answer": "Store", "isCorrect": false, "answered": false},
         ],
         "correctAnswers": [
             {"id": 1, "answer": "Staff", "isCorrect": true, "answered": false},
             {"id": 2, "answer": "Stave", "isCorrect": true, "answered": false}
         ]
     },
     {
         "id": 2,
         "category": "cats",
         "question": "What is this cat?",
         "answers": [],
         "possibles": [
             {"id": 1, "answer": "Cat-1", "isCorrect": false, "answered": false},
             {"id": 2, "answer": "Cat-2", "isCorrect": false, "answered": false},
             {"id": 3, "answer": "Cat-3", "isCorrect": false, "answered": false},
             {"id": 4, "answer": "Cat-4", "isCorrect": false, "answered": false}
         ],
         "correctAnswers": [
             {"id": 2, "answer": "Cat-2", "isCorrect": true, "answered": false}
         ]
     }
 ]