Swift4 中的 JSONDecoder 来自嵌套 JSON

Question

使用Swift4、iOS11.1、Xcode9.1，

尝试在 Swift4 的可解码结构中匹配 JSON 文件，最终得到以下错误消息:

"Expected to decode Array<Any> but found a dictionary instead." --> 发现两个拼写错误后 - 仍然有问题!

错误消息现在显示:The Error-Messages now says: intValue: Optional(5))], debugDescription: "No value associated with key photos (\"photos\").", underlyingError: nil))

坐标结构内部的坐标初始化器(参见下面的代码)，我得到了以下post 。我尝试与 JSON 文件完全匹配的其他所有内容(参见最底部)...

目前，我没有看到任何拼写错误 - 难道我还遗漏了其他内容吗？

JSON 文件的获取方式如下。这里可能有什么问题吗？

    let myTask = session.dataTask(with: myRequest) { (data, response, error) in

        if (error != nil) {
            print("Error1 fetching JSON data")
        }
        else {
            do {
                //Decode retrived data with JSONDecoder and assing type of Station object
                let stationData = try JSONDecoder().decode(Station.self, from: data!)

                //Get back to the main queue
                DispatchQueue.main.async {
                    print(stationData)
                }
            }
            catch let error {
                print(error)
            }
        }
    }
    myTask.resume()

该结构如下所示(请参阅下面的 JSON):

struct Station: Codable {

    let htmlAttributions: [String]
    let nextPageToken: String
    let results: [Result]
    let status: String

    struct Result: Codable {
        let formattedAddress: String
        let geometry: Geometry
        let icon: String
        let id: String
        let name: String
        let photos: [Photo]
        let placeID: String
        let rating: Double
        let reference: String
        let types: [String]

        struct Geometry: Codable {
            let location: Coordinates
            let viewport: Viewport

            struct Coordinates: Codable {
                let lat: Double
                let lng: Double
                init(from decoder: Decoder) throws {
                    let values = try decoder.container(keyedBy: CodingKeys.self)
                    lat = try values.decode(Double.self, forKey: .lat)
                    lng = try values.decode(Double.self, forKey: .lng)
                }
                enum CodingKeys : String, CodingKey {
                    case lat
                    case lng
                }
            }

            struct Viewport: Codable {
                let northeast: Coordinates
                let southwest: Coordinates

                enum CodingKeys : String, CodingKey {
                    case northeast
                    case southwest
                }
            }

            enum CodingKeys : String, CodingKey {
                case location
                case viewport
            }
        }
        // !!!!!!!!!!!! something wrong here ???? !!!!!!!!!!!
        struct Photo: Codable {

            let height: Int
            let htmlAttributions: [String]
            let photoReference: String
            let width: Int
            enum CodingKeys : String, CodingKey {
                case height
                case htmlAttributions = "html_attributions"
                case photoReference = "photo_reference"
                case width
            }
        }

        enum CodingKeys : String, CodingKey {
            case formattedAddress = "formatted_address"
            case geometry
            case icon
            case id
            case name
            case photos
            case placeID = "place_id"
            case rating
            case reference
            case types
        }
    }

    enum CodingKeys : String, CodingKey {
        case htmlAttributions = "html_attributions"
        case nextPageToken = "next_page_token"
        case results
        case status
    }
}

这是 JSON 文件:

{
   "html_attributions" : [],
   "next_page_token" : "F3ddaOzOcyo94AA2skDm",
   "results" : [
      {
         "formatted_address" : "Strasse 1, 6003 Luzern, Switzerland",
         "geometry" : {
            "location" : {
               "lat" : 47.04951260000001,
               "lng" : 8.310404999999999
            },
            "viewport" : {
               "northeast" : {
                  "lat" : 47.0508615802915,
                  "lng" : 8.311753980291503
               },
               "southwest" : {
                  "lat" : 47.0481636197085,
                  "lng" : 8.309056019708498
               }
            }
         },
         "icon" : "https://maps.gstatic.com/mapfiles/place_api/icons/generic_business-71.png",
         "id" : "a3d600a6e78105b6ce2b5f5a3fac98ca1910a09b",
         "name" : "Luzern",
         "photos" : [
            {
               "height" : 4000,
               "html_attributions" : [
                  "\u003ca href=\"https://maps.google.com/maps/contrib/113951418385089253589/photos\"\u003eAlex Marcu\u003c/a\u003e"
               ],
               "photo_reference" : "CmRaAAAAYHK1VHDFlkbzXuMnF2MLEdew-36lgHC2lS1Cxg_DELgP-ckZH7G6aa-81LGDpR5rPZY1XMw64mytsjXIrdB5n3QQmXjGgelwZEbHaetT2jpy9SeaHDH3qUGGAUW-7BtZEhCxXy2dxGSv6A_g7fipsCr5GhRZlPuliykokXIkqfqIN_vMWzmYyA",
               "width" : 3000
            }
         ],
         "place_id" : "ChIJqQIbhpj7j0cRjUguIM__gZw",
         "rating" : 4.4,
         "reference" : "CmRSAAAAzBZCshpypXcbMhrBQIdK2zISd3Q40QRSFO0KKhIrTejnGiZIoASuVqCVtmNBnFsodLWrYtOP-RmwCqDBDVbMheeCbFk7f0L8gwixLx_SGhYTDqPd6B2IwPWWXH5Pb6lxEhBoQtWj-kB-g1ZiOZ74hswNGhSd9Kf9Qj1P2_fdQCTO_VCoTU09JA",
         "types" : [
            "transit_station",
            "bus_station",
            "train_station",
            "point_of_interest",
            "establishment"
         ]
      },
      { ...more results... },
      { ...more results... }
   ],
   "status" : "OK"
}

Answer 1

错误消息表明 results 数组的第 6 个元素(索引 5)没有键 photos。

简单的解决方案是将数组声明为可选

let photos: [Photo]?

广泛的解决方案是添加一个初始值设定项以便能够分配默认的非可选值。