json - 解码 JSON 对象(发送带参数的 GET 请求) - Swift 4 Decodable

Question

考虑以下要点:https://gist.github.com/anonymous/0703a591f97fa9f6ad35b29234805fbd - 没有有效的方式来显示所有相关信息，因为文件相当长。道歉

我有一些我正在尝试解码的嵌套 JSON 对象。

{  
   "establishments":[  
      { ... }
   ],
   "meta":{ ... },
   "links":[  

   ]
}

^ establishments数组包含 Establishment对象

我的代码成功运行到 ViewController.swift 的第 7 行我实际上在使用 Swift 4 的地方 JSONDecode()功能。

ViewController.swift

let jsonURLString = "http://api.ratings.food.gov.uk/Establishments?address=\(self.getPostalCode(place: place))&latitude=\(place.coordinate.latitude.description)&longitude=\(place.coordinate.longitude.description)&maxDistanceLimit=0&name=\(truncatedEstablishmentName[0].replacingOccurrences(of: "'", with: ""))"

guard let url = URL(string: jsonURLString) else { print("URL is invalid"); return }

URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
    guard let data = data, error == nil, response != nil else {
        print("Something went wrong")
        return
    }
    //print("test")
    do {
        let establishments = try JSONDecoder().decode(Establishments.self, from: data)
        print(establishments)
    } catch {
        print("summots wrong")
    }

}).resume()

我在 Establishment.swift 中看到的映射 JSON 对象的输出是: summots wrong - 第 11 行，共 ViewController.swift .

我相信它没有按预期工作的原因是因为 JSON 格式是这样的:

{  
   "establishments":[ ... ],
   "meta":{ ... },
   "links":[  ]
}

但我不知道我的类结构/我在 View Controller 中所做的事情是否满足此布局标准。

谁能发现我哪里出错了？我认为这是非常基本的东西，但我似乎无法理解它

我也明白我不应该用大写字母来命名类的属性 - 为打破任何约定而道歉

编辑:我打印了错误而不是我自己的语句，如下所示:

而不是: print("summots wrong")
我写道: print(error)

dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.})))

正如 Hamish 正确指出的那样，我没有从 GET 请求中收到正确的 JSON 数据。事实上，我根本没有收到任何 JSON。当 x-api-version 出现时，我使用的 API 默认为 XML 格式。未设置为 2 .

而不是 //print("test")在我的 ViewController.swift文件，我使用了推荐的: print(String(data: data, encoding: .utf8))线

我使用了带有以下标题的 Postman: x-api-version: 2 , accept: application/json和 content-type: application/json检索我的 JSON 输出。如果我在浏览器窗口中使用相同的 GET 字符串(正确填写所有参数)，我将收到一条错误消息: The API 'Establishments' doesn't exist以 XML 格式。

有什么办法可以让我发送带有此 URL 的 header 吗？

编辑 2:我已更改使用请求 URLRequest而不仅仅是 URL .

这是我更新的 ViewController.swift代码:

let jsonURLString = "http://api.ratings.food.gov.uk/Establishments?address=\(self.getPostalCode(place: place))&latitude=\(place.coordinate.latitude.description)&longitude=\(place.coordinate.longitude.description)&maxDistanceLimit=0&name=\(truncatedEstablishmentName[0].replacingOccurrences(of: "'", with: ""))"

guard let url = URL(string: jsonURLString) else { print("URL is invalid"); return }
var request = URLRequest(url: url)
request.httpMethod = "GET"
request.addValue("x-api-version", forHTTPHeaderField: "2")
request.addValue("accept", forHTTPHeaderField: "application/json")
request.addValue("content-type", forHTTPHeaderField: "application/json")

URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
   guard let data = data, error == nil, response != nil else {
       print("Something went wrong")
       return
   }
   print(String(data: data, encoding: .utf8))
// do {
//     let establishments = try JSONDecoder().decode(Establishments.self, from: data)
//     print(establishments)
// } catch {
//     print(error)
// }

}).resume()

我收到错误: HTTP Error 400. The request has an invalid header name
我做了一些检查，请求只是忽略了 x-api-version header 值为 2。

有任何想法吗？

编辑 3: addValue 的正确格式本来应该: request.addValue("2", forHTTPHeaderField: 'x-api-version等等。

我现在面临着类声明的问题，特别是在我的“元”类中。
Meta.(CodingKeys in _DF4B170746CD5543281B14E0B0E7F6FB).dataSource], debugDescription: "Expected String value but found null instead.", underlyingError: nil
它在提示是因为我的类声明与它期望的来自 JSON 对象的数据不匹配。

在我的 JSON 响应中(引用要点)有两个 meta对象，一个包含值 null为 dataSource另一个是 Lucene .

有什么方法可以让我在类初始值设定项中接受“空”值和字符串，同时遵守可解码协议(protocol)？

JSON 响应的那部分对我来说已经死了，我是否仍然需要为它创建对象，或者我可以忽略它们而逃脱？ - 没有声明任何东西。或者我是否特别需要记下 JSON 响应中的所有内容才能使用数据？

Answer 1

要自动解码，您的模型类属性必须与响应值类型匹配。从 JSON 响应中，我可以看到很少有数据模型属性与 JSON 值类型不匹配。例如:

//inside response
"Hygiene": 10, // which is integer type

// properties in Scores
let Hygiene: String

您必须将模型类属性更改为响应或 JSON 响应作为您的类属性。

为了演示，我已通过以下更改修改了您的模型类:

        // changed from String
        let Hygiene: Int 
        let Structural: Int
        let ConfidenceInManagement: Int

        // changed from Double
        let longitude: String
        let latitude: String

        // changed to optional
        let dataSource: String?
        let returncode: String?

        // changed from Int
        let RatingValue: String

用以下更改替换您的模型类:

class Scores: Decodable {
        // set as string because we can expect values such as 'exempt'
        let Hygiene: Int
        let Structural: Int
        let ConfidenceInManagement: Int

        init(Hygiene: Int, Structural: Int, ConfidenceInManagement: Int) {
            self.Hygiene = Hygiene
            self.Structural = Structural
            self.ConfidenceInManagement = ConfidenceInManagement
        }
    }

    class Geocode: Decodable {
        let longitude: String
        let latitude: String

        init(longitude: String, latitude: String) {
            self.longitude = longitude
            self.latitude = latitude
        }
    }

    class Meta: Decodable {
        let dataSource: String?
        let extractDate: String
        let itemCount: Int
        let returncode: String?
        let totalCount: Int
        let totalPages: Int
        let pageSize: Int
        let pageNumber: Int

        init(dataSource: String, extractDate: String, itemCount: Int, returncode: String, totalCount: Int, totalPages: Int, pageSize: Int, pageNumber: Int) {

            self.dataSource = dataSource
            self.extractDate = extractDate
            self.itemCount = itemCount
            self.returncode = returncode
            self.totalCount = totalCount
            self.totalPages = totalPages
            self.pageSize = pageSize
            self.pageNumber = pageNumber
        }
    }

    class Establishments: Decodable {
        let establishments: [Establishment]

        init(establishments: [Establishment]) {
            self.establishments = establishments
        }
    }

    class Establishment: Decodable {
        let FHRSID: Int
        let LocalAuthorityBusinessID: String
        let BusinessName: String
        let BusinessType: String
        let BusinessTypeID: Int
        let AddressLine1: String
        let AddressLine2: String
        let AddressLine3: String
        let AddressLine4: String
        let PostCode: String
        let Phone: String
        let RatingValue: String
        let RatingKey: String
        let RatingDate: String
        let LocalAuthorityCode: Int
        let LocalAuthorityName: String
        let LocalAuthorityWebSite: String
        let LocalAuthorityEmailAddress: String
        let scores: Scores
        let SchemeType: String
        let geocode: Geocode
        let RightToReply: String
        let Distance: Double
        let NewRatingPending: Bool
        let meta: Meta
        let links: [String]

        init(FHRSID: Int, LocalAuthorityBusinessID: String, BusinessName: String, BusinessType: String, BusinessTypeID: Int, AddressLine1: String, AddressLine2: String, AddressLine3: String, AddressLine4: String, PostCode: String, Phone: String, RatingValue: String, RatingKey: String, RatingDate: String, LocalAuthorityCode: Int, LocalAuthorityName: String, LocalAuthorityWebSite: String, LocalAuthorityEmailAddress: String, scores: Scores, SchemeType: String, geocode: Geocode, RightToReply: String, Distance: Double, NewRatingPending: Bool, meta: Meta, links: [String]) {

            self.FHRSID = FHRSID
            self.LocalAuthorityBusinessID = LocalAuthorityBusinessID
            self.BusinessName = BusinessName
            self.BusinessType = BusinessType
            self.BusinessTypeID = BusinessTypeID
            self.AddressLine1 = AddressLine1
            self.AddressLine2 = AddressLine2
            self.AddressLine3 = AddressLine3
            self.AddressLine4 = AddressLine4
            self.PostCode = PostCode
            self.Phone = Phone
            self.RatingValue = RatingValue
            self.RatingKey = RatingKey
            self.RatingDate = RatingDate
            self.LocalAuthorityCode = LocalAuthorityCode
            self.LocalAuthorityName = LocalAuthorityName
            self.LocalAuthorityWebSite = LocalAuthorityWebSite
            self.LocalAuthorityEmailAddress = LocalAuthorityEmailAddress
            self.scores = scores
            self.SchemeType = SchemeType
            self.geocode = geocode
            self.RightToReply = RightToReply
            self.Distance = Distance
            self.NewRatingPending = NewRatingPending
            self.meta = meta
            self.links = links
        }
    }

希望它会奏效。