使用 Swift 中的 Decodable 解析嵌套 JSON

Question

我正在尝试解析此 JSON 响应

    {
    "payload": {
        "bgl_category": [{
            "number": "X",
            "name": "",
            "parent_number": null,
            "id": 48488,
            "description": "Baustellenunterk\u00fcnfte, Container",
            "children_count": 6
        }, {
            "number": "Y",
            "name": "",
            "parent_number": null,
            "id": 49586,
            "description": "Ger\u00e4te f\u00fcr Vermessung, Labor, B\u00fcro, Kommunikation, \u00dcberwachung, K\u00fcche",
            "children_count": 7
        }]
    },
    "meta": {
        "total": 21
    }
}

我有兴趣在我的 TableViewCell 中查看的只有 number 和 description

这是我到目前为止所做的努力：

    //MARK: - BGLCats
struct BGLCats: Decodable {

        let meta : Meta!
        let payload : Payload!
        
}

//MARK: - Payload
struct Payload: Decodable {

        let bglCategory : [BglCategory]!
        
}

//MARK: - BglCategory
struct BglCategory: Decodable {

        let descriptionField : String
        let id : Int
        let name : String
        let number : String
        let parentNumber : Int
        
}

//MARK: - Meta
struct Meta: Decodable {

        let total : Int
        
}

API 请求：

    fileprivate func getBgls() {
        
        guard let authToken = getAuthToken() else {
            return
        }
        
        let headers  = [
            "content-type" : "application/json",
            "cache-control": "no-cache",
            "Accept"       : "application/json",
            "Authorization": "\(authToken)"
        ]
        
        let request = NSMutableURLRequest(url: NSURL(string: "https://api-dev.com")! as URL, cachePolicy: .useProtocolCachePolicy, timeoutInterval: 10.0)
        
        request.allHTTPHeaderFields = headers
        
        let endpoint  = "https://api-dev.com"
        guard let url = URL(string: endpoint) else { return }
        
        URLSession.shared.dataTask(with: request as URLRequest) {(data, response, error) in
            guard let data = data else { return }
            
            do {
                let BGLList = try JSONDecoder().decode(BglCategory.self, from: data)
                print(BGLList)
                
                DispatchQueue.main.sync { [ weak self] in
                    self?.number = BGLList.number
                    self?.desc   = BGLList.descriptionField
//                    self?.id  = BGLList.id

                    print("Number: \(self?.number ?? "Unknown" )")
                    print("desc: \(self?.desc ?? "Unknown" )")
//                    print("id: \(self?.id ?? 0 )")
                }
            } catch let jsonError {
                print("Error Serializing JSON:", jsonError)
            }
            
       }.resume()
    }

但我收到错误消息：

Error Serializing JSON: keyNotFound(CodingKeys(stringValue: "childrenCount", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"childrenCount\", intValue: nil) (\"childrenCount\").", underlyingError: nil))

Answer 1

问题是 JSON解码器不知道 bglCategory 在 JSON 有效负载中表示为 bgl_category。如果 JSON 名称与您需要对 Decodable

实施 CodingKeys 的变量名称不同

你的情况：

struct BglCategory: Decodable {
  
  let descriptionField : String
  let id : Int
  let name : String
  let number : String
  let parentNumber : Int?
  
  enum CodingKeys: String, CodingKey {
    case id, name, number
    case descriptionField = "description"
    case parentNumber = "parent_number"
  }
}

struct Payload: Decodable {
  
  let bglCategory : [BglCategory]!
  
  enum CodingKeys: String, CodingKey {
    case bglCategory = "bgl_category"
  }
  
}

Answer 2

这里有一些问题。

您（大部分）正确地创建了模型，但只有两处不匹配：

struct BglCategory: Decodable {

   let description : String // renamed, to match "description" in JSON
   let parentNum: Int?      // optional, because some values are null
   // ...
}

第二个问题是您的模型属性是 camelCased 而 JSON 是 snake_cased。 JSON解码器有一个 .convertFromSnakeCase 策略来自动处理它。解码前需要先在解码器上设置。

第三个问题是您需要解码根对象 BGLCats，而不是 BglCategory。

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase // set the decoding strategy

let bglCats = try decoder.decode(BGLCats.self, from: data) // decode BGLCats

let blgCategories = bglCats.payload.bglCategory

使用 Swift 中的 Decodable 解析嵌套 JSON

Parsing nested JSON using Decodable in Swift

json

swift

decodable