Question

我正在请求API向我发送一些我可以成功检索的数据，但我仍陷入其解码过程中。这是我收到的JSON：

ERROR:  syntax error at or near "FROM"

我正在尝试创建以下结构来解码它：

[  
   {  
      "challenge_id":1,
      "challenge_title":"newchallenge1",
      "challenge_pts_earned":1000,
      "challenge_description":"description1",
      "start_date":"2017-09-24T00:00:00.000Z",
      "end_date":"2017-09-24T00:00:00.000Z",
      "challenge_category_id":1,
      "status_id":2,
      "createdAt":"2017-09-24T17:21:47.000Z",
      "updatedAt":"2017-09-24T09:40:34.000Z"
   },
   {  
      "challenge_id":2,
      "challenge_title":"challenge1",
      "challenge_pts_earned":100,
      "challenge_description":"description1",
      "start_date":"2017-09-24T00:00:00.000Z",
      "end_date":"2017-09-24T00:00:00.000Z",
      "challenge_category_id":1,
      "status_id":0,
      "createdAt":"2017-09-24T17:22:12.000Z",
      "updatedAt":"2017-09-24T09:22:12.000Z"
   },
   {  
      "challenge_id":3,
      "challenge_title":"new eat title",
      "challenge_pts_earned":600000,
      "challenge_description":"haha",
      "start_date":"2017-01-09T00:00:00.000Z",
      "end_date":"2017-01-10T00:00:00.000Z",
      "challenge_category_id":2,
      "status_id":0,
      "createdAt":"2017-09-27T17:12:10.000Z",
      "updatedAt":"2017-09-27T09:15:19.000Z"
   }
]

这是我的实施代码：

   struct challenge : Codable {
    let  id : String?
    let  title : String?
    let  pointsEarned : String?
    let  description : String?
    let  dayStarted : String?
    let  dayEnded : String?
    let  categoryID : String?
    let  statusID : Int?
    let createdAt : Date?
    let updatedAt : Date?

    enum CodingKeys: String, CodingKey {
        case id = "challenge_id"
        case title = "challenge_title"
        case pointsEarned = "challenge_pts_earned"
        case description = "challenge_description"
        case dayStarted = "start_date"
        case dayEnded = "end_date"
        case categoryID = "challenge_category_id"
        case statusID = "status_id"
        case createdAt, updatedAt
    }

}

然而，当我尝试调试它时，我永远不能输入

的if语句

 var All_challenges : [challenge]?
 let url = URL(string: API.all_challenges.rawValue)!
        var request = URLRequest(url: url)
        request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
        request.httpMethod = "GET"
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {
                print("error=\(String(describing: error))")
                return
            }
            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {
                print("statusCode should be 200, but is \(httpStatus.statusCode)")
                print("\(String(describing: response))")
            }
            let responseString = String(data: data, encoding: .utf8)
            guard let result = responseString else { return }
            print(result)
           if let json = try? JSONDecoder().decode([challenge].self , from : data ) {
                self.All_challenges = json

           }

         }
        task.resume()

请给我一些关于我的错误的描述，我对JSON配对非常陌生

Answer 1

请抓住错误并阅读

输入'String'不匹配。
调试说明：预计会解码String但会找到一个数字。

您收到challenge_id，challenge_pts_earned，challenge_category_id和status_id的错误，因为值为Int（实际上您已经注意到了JSON）

其次，由于您未提供日期策略（默认值为Date），因此无法解码TimeInterval值。您必须提供自定义日期格式化程序以使用小数秒来解码ISO8601。

最后，如评论中所述，通过指定CodingKeys使用 camelCased 变量名称，并且因为JSON包含始终所有键都将属性声明为非可选

let jsonString = """
[
{
"challenge_id":1,
"challenge_title":"newchallenge1",
"challenge_pts_earned":1000,
"challenge_description":"description1",
"start_date":"2017-09-24T00:00:00.000Z",
"end_date":"2017-09-24T00:00:00.000Z",
"challenge_category_id":1,
"status_id":2,
"createdAt":"2017-09-24T17:21:47.000Z",
"updatedAt":"2017-09-24T09:40:34.000Z"
},
{
"challenge_id":2,
"challenge_title":"challenge1",
"challenge_pts_earned":100,
"challenge_description":"description1",
"start_date":"2017-09-24T00:00:00.000Z",
"end_date":"2017-09-24T00:00:00.000Z",
"challenge_category_id":1,
"status_id":0,
"createdAt":"2017-09-24T17:22:12.000Z",
"updatedAt":"2017-09-24T09:22:12.000Z"
},
{
"challenge_id":3,
"challenge_title":"new eat title",
"challenge_pts_earned":600000,
"challenge_description":"haha",
"start_date":"2017-01-09T00:00:00.000Z",
"end_date":"2017-01-10T00:00:00.000Z",
"challenge_category_id":2,
"status_id":0,
"createdAt":"2017-09-27T17:12:10.000Z",
"updatedAt":"2017-09-27T09:15:19.000Z"
}
]
"""

struct Challenge : Decodable {

//    private enum CodingKeys : String, CodingKey {
//        case challengeId = "challenge_id"
//        case challengeTitle = "challenge_title"
//        case challengePtsEarned = "challenge_pts_earned"
//        case challengeDescription = "challenge_description"
//        case startDate = "start_date"
//        case endDate = "end_date"
//        case challengeCategoryId = "challenge_category_id"
//        case statusId = "status_id"
//        case createdAt, updatedAt
//    }

    let challengeId : Int
    let challengeTitle : String
    let challengePtsEarned : Int
    let challengeDescription : String
    let startDate : String // or Date
    let endDate : String // or Date
    let challengeCategoryId : Int
    let statusId : Int
    let createdAt : Date
    let updatedAt : Date
}

let data = Data(jsonString.utf8)
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SZ"
formatter.locale = Locale(identifier: "en_US_POSIX")
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(formatter)
decoder.keyDecodingStrategy = .convertFromSnakeCase 
do {
    let challenges = try decoder.decode([Challenge].self, from: data)
    print(challenges)
} catch { print(error) }

注意：

在开发JSON en- / decode时，强烈建议使用全套错误处理。它使调试变得更加容易

do {
   try JSONDecoder().decode ...

} catch DecodingError.dataCorrupted(let context) {
    print(context)
} catch DecodingError.keyNotFound(let key, let context) {
    print("Key '\(key)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.valueNotFound(let value, let context) {
    print("Value '\(value)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.typeMismatch(let type, let context)  {
    print("Type '\(type)' mismatch:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch {
    print("error: ", error)
}

修改

在Swift 4.1及更高版本中，您可以通过添加keyDecodingStrategy

来省略CodingKeys

decoder.keyDecodingStrategy = .convertFromSnakeCase

Answer 2

您的代码中有多处错误。首先，你的一些变量类型是错误的。所有id和challenge_pts_earned都必须属于Int类型。您可以轻松发现这一点，因为在JSON字符串中需要用引号分隔。解码Date时，您还需要指定要使用的日期格式。

startDate和endDate也是日期，因此即使它们可以解码为String s，我建议您将它们存储为实际Date个对象

还要符合Swift命名约定，它是类型的upperCamelCase和变量和函数名称的lowerCamelCase。您可以使用符合CodingKey的自定义类型将自定义变量名称映射到其JSON表示。

struct Challenge : Decodable {
    let id: Int?
    let title: String?
    let pointsEarned: Int?
    let description: String?
    let startDate: String?
    let endDate: String?
    let categoryId: Int?
    let statusId: Int?
    let createdAt: Date?
    let updatedAt: Date?

    private enum CodingKeys: String, CodingKey {
        case id = "challenge_id"
        case title = "challenge_title"
        case pointsEarned = "challenge_pts_earned"
        case description = "challenge_description"
        case startDate = "start_date"
        case endDate = "end_date"
        case categoryId = "challenge_category_id"
        case statusId = "status_id"
        case createdAt
        case updatedAt
    }

    static var dateFormatter: DateFormatter {
        let df = DateFormatter()
        df.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
        df.locale = Locale(identifier: "en_US_POSIX")
        return df
    }
}

do {
    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .formatted(Challenge.dateFormatter)
    let decoded = try decoder.decode([Challenge].self, from: jsonArrayResponse.data(using: .utf8)!)
} catch {
    print(error)
}

如何使用Decodable解码JSON数组？

2 个答案: