Question

我正在编写一个应用，试图通过Codable将数组中的数组保存到UserDefaults中，但是它崩溃了，并出现以下错误：

由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'，原因：'-[Here.UserEntries encodeWithCoder：]：无法识别的选择器已发送到实例 0x600000649e70'

这是我的保存方式：

class UserEntries: NSObject, Codable {
    struct Question : Codable {
        var question: String
        var answer: String

        enum CodingKeys: String, CodingKey {
            case question
            case answer
        }

        init(question: String, answer: String) {
            self.question = question
            self.answer = answer
        }
        func encode(to encoder: Encoder) throws {
            var container = encoder.container(keyedBy: CodingKeys.self)
            try container.encode(question, forKey: .question)
            try container.encode(answer, forKey: .answer)
        }
        init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            question = try container.decode(String.self, forKey: .question)
            answer = try container.decode(String.self, forKey: .answer)
        }
    }

    var date: String
    var questions: [Question]

    enum CodingKeys: String, CodingKey {
        case date
        case questions
    }

    init(date: String, questions: [Question]) {
        self.date = date
        self.questions = questions
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(date, forKey: .date)
        try container.encode(questions, forKey: .questions)
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        date = try container.decode(String.self, forKey: .date)
        questions = [try container.decode(Question.self, forKey: .questions)]
    }
}

其中userEntry是：

let userEntry = UserEntries(date: String(todayDate), questions: [UserEntries.Question(question: q1Text, answer: q1Answer), UserEntries.Question(question: q2Text, answer: q2Answer)])

然后

UserDefaults.standard.set(NSKeyedArchiver.archivedData(withRootObject: userEntry), forKey: "allEntries")

到底出了什么问题？我有种无法将数组保存在数组中的感觉，但是该如何解决？

Answer 1

此行：

questions = [try container.decode(Question.self, forKey: .questions)]

不正确。要获取Question的数组，您应该解码数组[Question].self的类型：

questions = try container.decode([Question].self, forKey: .questions)

此外，请注意Decodable / Encodable与JSONDecoder / JSONEncoder一起使用，请参见official docs。据此，这是您需要保存的内容（编码为数据然后保存）：

let jsonEncoder = JSONEncoder()
if let value = try? jsonEncoder.encode(userEntry) {
    UserDefaults.standard.set(value, forKey: "allEntries")
}

相反，获取数据，如果是，则尝试解码对象：

let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
   let userEntry = try? jsonDecoder.decode(UserEntries.self, from: data) {

   // here you get userEntry
}

示例：

let userEntry = UserEntries(date: "1 Sep 18",
    questions: [
        UserEntries.Question(question: "q1Text", answer: "q1Answer"),
        UserEntries.Question(question: "q2Text", answer: "q2Answer")
    ])

let jsonEncoder = JSONEncoder()
if let value = try? jsonEncoder.encode(userEntry) {
    UserDefaults.standard.set(value, forKey: "allEntries")
}

let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
    let userEntry = try? jsonDecoder.decode(UserEntries.self, from: data) {

    print(userEntry.date) // 1 Sep 18
}

Swift-使用Codeable崩溃对象保存应用

1 个答案: