JSON、Swift 4.1 的编码关键难点

Question

我有一个响应正文如下所示的 JSON：

{
    "Count": 116,
    "Message": "Result returned successfully",
    "SearchCriteria": "Search Criteria",
    "Results": [
        {
            "Value": "",
            "ValueId": "",
            "Variable": "Suggested VIN",
            "VariableId": 142
        },
        < 115 more like this >
    ]
}

初步尝试

我最初尝试创建编码键，如下所示：

struct ResponseBody: Codable {
    var count: Int
    var message: String
    var searchCriteria: String
    var results: [Result]

    enum ResponseKeys: String, CodingKey {
        case count = "Count"
        case message = "Message"
        case searchCriteria = "SearchCriteria"
        case results = "Results"
    }
}

struct Result: Codable {
    var value: String?
    var valueId: String?
    var variable: String
    var variableId: Int

    enum ResultKeys: String, CodingKey {
        case value = "Value"
        case valueID = "ValueId"
        case variable = "Variable"
        case variableID = "VariableId"
    }
}

在编译器没有抱怨的情况下，我尝试使用以下代码对其进行解码：

// network request code
    let decoder = JSONDecoder()
    var responseData: ResponseBody?

    do {
      responseData = try decoder.decode(ResponseBody.self, from: data)
      guard let responseData = responseData else { return }
      let vehicle = self.createVehicleStruct(from: responseData)
      self.dispatchGroup.notify(queue: .main, execute: {
        completion(vehicle)
      })
    } catch {
      print(error, error.localizedDescription)
    }

产生了这个error：

keyNotFound(CodingKeys(stringValue: "count", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "否 与键 CodingKeys 关联的值（stringValue: \"count\", intValue: nil) (\"count\").", underlyingError: nil)) 无法读取数据 因为它不见了。

工作，但可怕的尝试

渴望“继续前进”，我尝试了以下方法，并且能够解析 JSON，但不符合 Swift 命名约定让我很生气：

struct ResponseBody: Codable {
    var Count: Int
    var Message: String
    var SearchCriteria: String
    var Results: [Result]
}

struct Result: Codable {
    var Value: String?
    var ValueId: String?
    var Variable: String
    var VariableId: Int
}

现在，我又开始尝试在我的structs 中获得漂亮、干净的名称，因为我知道网络部分可以正常工作。经过进一步调查，我需要提供一个init(from decoder:)，所以我重构如下：

struct ResponseBody: Decodable {
    var count: Int
    var message: String
    var searchCriteria: String
    var results: [Result]

    private enum CodingKeys: String, CodingKey {
        case count = "Count"
        case message = "Message"
        case searchCriteria = "SearchCriteria"
        case results = "Results"
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let count: Int = try container.decode(Int.self, forKey: .count)
        let message: String = try container.decode(String.self, forKey: .message)
        let searchCriteria: String = try container.decode(String.self, forKey: .searchCriteria)
        let results: [Result] = try container.decode([Result].self, forKey: .results)

        // FIXME: Extra argument 'message' in call
        self.init(count: count, message: message, searchCriteria: searchCriteria, results: [results])
    }
}

struct Result: Decodable {
    var value: String?
    var valueID: String?
    var variable: String
    var variableID: Int

    private enum CodingKeys: String, CodingKey {
        case value = "Value"
        case valueID = "ValueId"
        case variable = "Variable"
        case variableID = "VariableId"
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let value: String = try container.decode(String.self, forKey: .value)
        let valueID: String = try container.decode(String.self, forKey: .valueID)
        let variable: String = try container.decode(String.self, forKey: .variable)
        let variableID: Int = try container.decode(Int.self, forKey: .variableID)

        // FIXME: Extra argument 'valueID' in call
        self.init(value: value?, valueID: valueID?, variable: variable, variableID: variableID)
    }
}

当我调用 init 时，init(from decoder:) 出现错误：

Extra argument 'valueID' in call

我不知道我的错误在哪里。如果您有建议，我欢迎您的意见。感谢您的阅读。

Answer 1

您的枚举必须称为 CodingKeys，并且它们的案例名称必须与结构属性的名称匹配（例如，variableID 和 variableId 不相同，但它们必须相同）。

只要你解决了这个问题，一切都会好起来的。

因此，我能够使用这两个结构解析您提供的 JSON，没问题：

struct ResponseBody: Codable {
    var count: Int
    var message: String
    var searchCriteria: String
    var results: [Result]

    enum CodingKeys: String, CodingKey {
        case count = "Count"
        case message = "Message"
        case searchCriteria = "SearchCriteria"
        case results = "Results"
    }
}

struct Result: Codable {
    var value: String?
    var valueId: String?
    var variable: String
    var variableId: Int

    enum CodingKeys: String, CodingKey {
        case value = "Value"
        case valueId = "ValueId"
        case variable = "Variable"
        case variableId = "VariableId"
    }
}