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我在 SwiftUI 中需要一些帮助。

我在下面有一个接受 JSON 数据的模型。当我想将它初始化为一个空数组时，应该很简单，只是说明Answers，但是我怎样才能不将它初始化为一个数组而是一个空的单个数据集。

struct Answers: Identifiable, Decodable  {
    let id: Int
    let questionsUsersId: Int
    let reactions: [Reactions]

enum CodingKeys: String, CodingKey {
        case id = "questions_id"
        case questionsUsersId = "questions_users_id"
        case reactions = "reactions"
    }

init(from decoder: Decoder) throws {

    let container = try decoder.container(keyedBy: CodingKeys.self)

    self.id = try container.decodeIfPresent(Int.self, forKey: .id) ?? 0
    self.questionsUsersId = try container.decodeIfPresent(Int.self, forKey: .questionsUsersId) ?? 0
    self.reactions = try container.decodeIfPresent([Reactions].self, forKey: .reactions) ?? [Reactions]()
}


 }

我试过 var answer: Answers = Answers() 但得到以下错误：

//Missing argument for parameter 'from' in call
//Insert 'from: <#Decoder#>'

我想将它初始化为空的原因是因为我需要在数据模型为nil时交出它的默认值。（即我应该在 xxx 中写什么？）

 @ObservedObject var receiveAnswersViewModel = ReceiveAnswersViewModel()
  //abbreviate
            NavigationLink(destination: AnswerDetailView(answer: receiveAnswersViewModel.answer ?? xxx), isActive: $shouldNavigate) {
                    
                        ForEach(myPageViewModel.answers(forFilter: selectedFilter)?.answers ?? [Answers]()) { answer in
                         
                         AnswerCell(answer: answer)
                                .gesture(TapGesture()
                                                .onEnded({ _ in
                                                    //your action here
                                    self.answersId = answer.answersId
                                    receiveAnswersViewModel.fetchAnswers(answers_id: answersId ?? 0)
                                       }))
                         }
                    }

这就是我在上面尝试做的：使用 NavigationLink 显示几个单元格。（假设单元格是推文。）按下列表中的推文之一→在以按下的推文ID作为参数的视图模型中调用fetchAnswers func→返回特定的推文详细信息→将其放入答案模型→手它转到视图→导航到推文详细信息视图。

查看模型代码如下：

class ReceiveAnswersViewModel: ObservableObject {
@Published var answer: Answers?

func fetchAnswers(answers_id: Int){
//abbreviate
self.answer = try JSONDecoder().decode(Answers.self, from: data)
}

提前致谢。

4

1 回答 1

0

一个合理的方法是添加一个静态方法来创建一个空实例。在这种情况下，您还必须添加init方法

顺便说一下，以单数形式命名结构，一个实例可能代表一个Answer

struct Answer: Identifiable, Decodable  {
    let id: Int
    let questionsUsersId: Int
    let reactions: [Reactions]

    static let example = Answer(id: 0, questionsUsersId: 0, reactions: [])

    init(id: Int, questionsUsersId: Int, reactions: [Reactions]) {
        self.id = id
        self.questionsUsersId = questionsUsersId
        self.reactions = reactions
    }

...

然后你可以声明

var answer = Answer.example
于 2021-12-09T08:31:23.267 回答