在 iOS Swift 中使用可编码解析嵌套的 json 响应数据？答案

【问题标题】：Parsing nested json response data using codable in iOS Swift?在 iOS Swift 中使用可编码解析嵌套的 json 响应数据？
【发布时间】：2020-03-13 11:26:28
【问题描述】：

我正在尝试在 swift 4 中解析可解码的 json 数据。它打印 nil 值。我找不到这是什么问题？

这里是模型类：

public struct TaskID: Decodable {

let embedded: Embedded?
let count: Int?

enum CodingKeys: String, CodingKey {
    case count = "count"
    case embedded = "_embedded"
  }
}

 public struct Embedded: Decodable {


let task: [Task]?
enum CodingKeys: String, CodingKey {
       case task = "task"
   }

 }

public struct Task : Decodable {

let id : String?
let name: String?
let assignee: String?
let created: String?
let processDefinitionId: String?
enum CodingKeys: String, CodingKey {
    case id = "id"
    case name = "name"
    case assignee = "assignee"
    case created = "created"
    case processDefinitionId = "processDefinitionId"


 }

}

这里是json：

{
"_links": {
    "self": {
        "href": "/task"
    }
},
"_embedded": {

    "task": [
        {
            "_links": {
                "assignee": {
                    "href": "/user/demo"
                },
                "execution": {
                    "href": "/execution/1b64cf75-0616-11ea-8860-120ef5ab2c25"
                },
                "identityLink": {
                    "href": "/task/1b64f688-0616-11ea-8860-120ef5ab2c25/identity-links"
                },
                "processDefinition": {
                    "href": "/process-definition/quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25"
                },
                "processInstance": {
                    "href": "/process-instance/1b64cf75-0616-11ea-8860-120ef5ab2c25"
                },
                "self": {
                    "href": "/task/1b64f688-0616-11ea-8860-120ef5ab2c25"
                }
            },
            "_embedded": {
                "variable": []
            },
            "id": "1b64f688-0616-11ea-8860-120ef5ab2c25",
            "name": "Quick Evaluation",
            "assignee": "demo",
            "created": "2019-11-13T13:04:20.687+0000",
            "due": null,
            "followUp": null,
            "delegationState": null,
            "description": null,
            "executionId": "1b64cf75-0616-11ea-8860-120ef5ab2c25",
            "owner": null,
            "parentTaskId": null,
            "priority": 50,
            "processDefinitionId": "quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25",
            "processInstanceId": "1b64cf75-0616-11ea-8860-120ef5ab2c25",
            "taskDefinitionKey": "QuickEvaluation",
            "caseExecutionId": null,
            "caseInstanceId": null,
            "caseDefinitionId": null,
            "suspended": false,
            "formKey": "a8apps:suryoday:gng:v0.1.0:kycUpload",
            "tenantId": null
        },
        {
            "_links": {
                "assignee": {
                    "href": "/user/demo"
                },
                "execution": {
                    "href": "/execution/412a03b7-06ae-11ea-8860-120ef5ab2c25"
                },
                "identityLink": {
                    "href": "/task/412a2aca-06ae-11ea-8860-120ef5ab2c25/identity-links"
                },
                "processDefinition": {
                    "href": "/process-definition/quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25"
                },
                "processInstance": {
                    "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25"
                },
                "self": {
                    "href": "/task/412a2aca-06ae-11ea-8860-120ef5ab2c25"
                }
            },
            "_embedded": {
                "variable": [
                    {
                        "_links": {
                            "self": {
                                "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25/variables/loanAmount"
                            }
                        },
                        "_embedded": null,
                        "name": "loanAmount",
                        "value": "650000",
                        "type": "String",
                        "valueInfo": {}
                    },
                    {
                        "_links": {
                            "self": {
                                "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25/variables/firstName"
                            }
                        },
                        "_embedded": null,
                        "name": "firstName",
                        "value": "Kamesh",
                        "type": "String",
                        "valueInfo": {}
                    }
                ]
            },
            "id": "412a2aca-06ae-11ea-8860-120ef5ab2c25",
            "name": "Quick Evaluation",
            "assignee": "demo",
            "created": "2019-11-14T07:13:27.558+0000",
            "due": null,
            "followUp": null,
            "delegationState": null,
            "description": null,
            "executionId": "412a03b7-06ae-11ea-8860-120ef5ab2c25",
            "owner": null,
            "parentTaskId": null,
            "priority": 50,
            "processDefinitionId": "quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25",
            "processInstanceId": "412a03b7-06ae-11ea-8860-120ef5ab2c25",
            "taskDefinitionKey": "QuickEvaluation",
            "caseExecutionId": null,
            "caseInstanceId": null,
            "caseDefinitionId": null,
            "suspended": false,
            "formKey": "a8apps:suryoday:gng:v0.1.0:kycUpload",
            "tenantId": null
        }

    ]
},
"count": 13
}

这里是urlrequest：

 // MARK: - URLRequestConvertible
func asURLRequest() throws -> URLRequest {
    let url = try K.ProductionServer.baseURL.asURL()

    var urlRequest = URLRequest(url: url.appendingPathComponent(path))
    print(urlRequest)
    // HTTP Method
    urlRequest.httpMethod = method.rawValue

    let authToken = UserDefaults.standard.string(forKey: "authToken")
    let bearerToken: String = "Bearer " + (authToken ?? "")
    print("baearer token::\(bearerToken)")

    // Common Headers
    urlRequest.setValue(ContentType.json.rawValue, forHTTPHeaderField: HTTPHeaderField.acceptType.rawValue)
    urlRequest.setValue(ContentType.json.rawValue, forHTTPHeaderField: HTTPHeaderField.contentType.rawValue)
    urlRequest.setValue(bearerToken, forHTTPHeaderField: HTTPHeaderField.authentication.rawValue)

    // Parameters
    if let parameters = parameters {
        do {
            urlRequest.httpBody = try JSONSerialization.data(withJSONObject: parameters, options: [])
        } catch {
            throw AFError.parameterEncodingFailed(reason: .jsonEncodingFailed(error: error))
        }
    }

    return urlRequest
}

这里是 alamofire 请求：

 import Foundation
import Alamofire

public class APIClient {
@discardableResult
private static func performRequest<T:Decodable>(route:APIRouter, decoder: JSONDecoder = JSONDecoder(), completion:@escaping (AFResult<T>)->Void) -> DataRequest {

    return AF.request(route)
                    .responseDecodable (decoder: decoder){ (response: AFDataResponse<T>) in
                        completion(response.result)
                        print("framework response::",response.result)
    }
}

public static func taskID(id: String, completion:@escaping (AFResult< [TaskID]>)->Void) {

    performRequest(route: APIRouter.TaskById(id: id), completion: completion)
}


}//APIClient

最初它显示 Dictionary, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Dictionary 但找到了一个数组。 但现在我在控制台日志中得到了 nil。不知道为什么我得到 nil 值。根据我的 json 响应，结构是否正确？我正在努力获取嵌套数据。

任何帮助都非常感谢..

【问题讨论】：

这与您在过去几天发布的其他两个问题有什么区别？它们看起来非常相似。
@JoakimDanielson 最后两个问题我有编码键并希望解码字典但找到了一个数组。但现在我的值为零..你能帮我解决这个问题吗
@JoakimDanielson 现在我也有 url 请求代码
但是我和其他人已经尝试过一次用你的 json 帮助你，但你似乎仍然在为同样的事情而苦苦挣扎。我真的不明白这一点，因为什么都没有真正改变。您需要将可能的问题与您的代码、实际的 json 解码（这很好）以及您拥有的 AF 和 ApiClient 类分开
@JoakimDanielson，好的，我怀疑我是否需要在数组中传递结构名称或只传递类名。 public static func taskID(id: String, completion:@escaping (AFResult) 如果我通过 TaskID 它显示错误，期望解码 Dictionary 但找到一个数组。如果我更改为数组 [TaskID] 它打印 nil价值。

标签： json swift xcode nested codable

【解决方案1】：

你的结构是正确的。请参阅下面的操场以获取证据；我没有收到错误。 nil 是非常常见的结果，当您没有完整的数据集并且您假设响应中的某些可选字段是非可选的，只是因为您在样本数据中看到它（您的样本不一定具有代表性）。如果没有来自服务器的实际规范，您需要确定哪些字段无法解码，并且您可能需要获取一堆数据来确定哪些字段是真正可选的。您可以通过在上面的 AF 项目中添加错误处理代码或将您的响应粘贴到下面的操场中来做到这一点。无论哪种方式，解码错误都应该告诉您哪个字段不存在。

import PlaygroundSupport
import UIKit
import WebKit


public struct TaskID: Decodable {

let embedded: Embedded?
let count: Int?

enum CodingKeys: String, CodingKey {
    case count = "count"
    case embedded = "_embedded"
  }
}

 public struct Embedded: Decodable {


let task: [Task]?
enum CodingKeys: String, CodingKey {
       case task = "task"
   }

 }

public struct Task : Decodable {

let id : String?
let name: String?
let assignee: String?
let created: String?
let processDefinitionId: String?
enum CodingKeys: String, CodingKey {
    case id = "id"
    case name = "name"
    case assignee = "assignee"
    case created = "created"
    case processDefinitionId = "processDefinitionId"


 }

}


let data = """
{
"_links": {
    "self": {
        "href": "/task"
    }
},
"_embedded": {

    "task": [
        {
            "_links": {
                "assignee": {
                    "href": "/user/demo"
                },
                "execution": {
                    "href": "/execution/1b64cf75-0616-11ea-8860-120ef5ab2c25"
                },
                "identityLink": {
                    "href": "/task/1b64f688-0616-11ea-8860-120ef5ab2c25/identity-links"
                },
                "processDefinition": {
                    "href": "/process-definition/quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25"
                },
                "processInstance": {
                    "href": "/process-instance/1b64cf75-0616-11ea-8860-120ef5ab2c25"
                },
                "self": {
                    "href": "/task/1b64f688-0616-11ea-8860-120ef5ab2c25"
                }
            },
            "_embedded": {
                "variable": []
            },
            "id": "1b64f688-0616-11ea-8860-120ef5ab2c25",
            "name": "Quick Evaluation",
            "assignee": "demo",
            "created": "2019-11-13T13:04:20.687+0000",
            "due": null,
            "followUp": null,
            "delegationState": null,
            "description": null,
            "executionId": "1b64cf75-0616-11ea-8860-120ef5ab2c25",
            "owner": null,
            "parentTaskId": null,
            "priority": 50,
            "processDefinitionId": "quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25",
            "processInstanceId": "1b64cf75-0616-11ea-8860-120ef5ab2c25",
            "taskDefinitionKey": "QuickEvaluation",
            "caseExecutionId": null,
            "caseInstanceId": null,
            "caseDefinitionId": null,
            "suspended": false,
            "formKey": "a8apps:suryoday:gng:v0.1.0:kycUpload",
            "tenantId": null
        },
        {
            "_links": {
                "assignee": {
                    "href": "/user/demo"
                },
                "execution": {
                    "href": "/execution/412a03b7-06ae-11ea-8860-120ef5ab2c25"
                },
                "identityLink": {
                    "href": "/task/412a2aca-06ae-11ea-8860-120ef5ab2c25/identity-links"
                },
                "processDefinition": {
                    "href": "/process-definition/quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25"
                },
                "processInstance": {
                    "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25"
                },
                "self": {
                    "href": "/task/412a2aca-06ae-11ea-8860-120ef5ab2c25"
                }
            },
            "_embedded": {
                "variable": [
                    {
                        "_links": {
                            "self": {
                                "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25/variables/loanAmount"
                            }
                        },
                        "_embedded": null,
                        "name": "loanAmount",
                        "value": "650000",
                        "type": "String",
                        "valueInfo": {}
                    },
                    {
                        "_links": {
                            "self": {
                                "href": "/process-instance/412a03b7-06ae-11ea-8860-120ef5ab2c25/variables/firstName"
                            }
                        },
                        "_embedded": null,
                        "name": "firstName",
                        "value": "Kamesh",
                        "type": "String",
                        "valueInfo": {}
                    }
                ]
            },
            "id": "412a2aca-06ae-11ea-8860-120ef5ab2c25",
            "name": "Quick Evaluation",
            "assignee": "demo",
            "created": "2019-11-14T07:13:27.558+0000",
            "due": null,
            "followUp": null,
            "delegationState": null,
            "description": null,
            "executionId": "412a03b7-06ae-11ea-8860-120ef5ab2c25",
            "owner": null,
            "parentTaskId": null,
            "priority": 50,
            "processDefinitionId": "quickEvaluation:1:129ce2b1-0616-11ea-8860-120ef5ab2c25",
            "processInstanceId": "412a03b7-06ae-11ea-8860-120ef5ab2c25",
            "taskDefinitionKey": "QuickEvaluation",
            "caseExecutionId": null,
            "caseInstanceId": null,
            "caseDefinitionId": null,
            "suspended": false,
            "formKey": "a8apps:suryoday:gng:v0.1.0:kycUpload",
            "tenantId": null
        }

    ]
},
"count": 13
}
""".data(using: .utf8)!

let decoder = JSONDecoder()
do {
  let decoded = try decoder.decode(TaskID.self, from: data)
  print(decoded)
} catch ( let error ) {
  print(error.localizedDescription)
}

【讨论】：

感谢您的回答。我对此表示怀疑是否需要传入数组或类。 func taskID(id: String, completion:@escaping (AFResult)->Void
仍然面临同样的问题
现在我也有 url 请求代码.. 你能检查一下吗
包装器是TaskID，如我的示例所示。
不使用 AF responseDecodable，只需获取数据并自行解码，这样您就可以捕获解码错误并找出哪个字段失败。

【解决方案2】：

import Foundation

// MARK: - Task
struct Task: Codable {
let links: VariableLinks?
let embedded: TaskEmbedded?
let count: Int?

enum CodingKeys: String, CodingKey {
    case links = "_links"
    case embedded = "_embedded"
    case count = "count"
}
}

// MARK: - TaskEmbedded
struct TaskEmbedded: Codable {
let task: [TaskElement]?

enum CodingKeys: String, CodingKey {
case task = "task"
}
}

// MARK: - TaskElement
struct TaskElement: Codable {
let links: TaskLinks?
let embedded: TaskEmbeddedClass?
let id: String?
let name: String?
let assignee: String?
let created: String?
let due: String?
let followUp: String?
let delegationState: String?
let taskDescription: String?
let executionId: String?
let owner: String?
let parentTaskId: Int?
let priority: Int?
let processDefinitionId: String?
let processInstanceId: String?
let taskDefinitionKey: String?
let caseExecutionId: Int?
let caseInstanceId: Int?
let caseDefinitionId: Int?
let suspended: Bool?
let formKey: String?
let tenantId: Int?

enum CodingKeys: String, CodingKey {
case links = "_links"
case embedded = "_embedded"
case id = "id"
case name = "name"
case assignee = "assignee"
case created = "created"
case due = "due"
case followUp = "followUp"
case delegationState = "delegationState"
case taskDescription = "description"
case executionId = "executionId"
case owner = "owner"
case parentTaskId = "parentTaskId"
case priority = "priority"
case processDefinitionId = "processDefinitionId"
case processInstanceId = "processInstanceId"
case taskDefinitionKey = "taskDefinitionKey"
case caseExecutionId = "caseExecutionId"
case caseInstanceId = "caseInstanceId"
case caseDefinitionId = "caseDefinitionId"
case suspended = "suspended"
case formKey = "formKey"
case tenantId = "tenantId"
}
}

// MARK: - TaskEmbeddedClass
struct TaskEmbeddedClass: Codable {
let variable: [Variable]?

enum CodingKeys: String, CodingKey {
case variable = "variable"
}
}

// MARK: - Variable
struct Variable: Codable {
let links: VariableLinks?
let embedded: String?
let name: String?
let value: String?
let type: String?
let valueInfo: ValueInfo?

enum CodingKeys: String, CodingKey {
case links = "_links"
case embedded = "_embedded"
case name = "name"
case value = "value"
case type = "type"
case valueInfo = "valueInfo"
}
}

// MARK: - VariableLinks
struct VariableLinks: Codable {
let linksSelf: SelfClass?

enum CodingKeys: String, CodingKey {
case linksSelf = "self"
}
}

// MARK: - SelfClass
struct SelfClass: Codable {
let href: String?

enum CodingKeys: String, CodingKey {
case href = "href"
}
}

// MARK: - ValueInfo
struct ValueInfo: Codable {
}

// MARK: - TaskLinks
struct TaskLinks: Codable {
let assignee: SelfClass?
let execution: SelfClass?
let identityLink: SelfClass?
let processDefinition: SelfClass?
let processInstance: SelfClass?
let linksSelf: SelfClass?

enum CodingKeys: String, CodingKey {
case assignee = "assignee"
case execution = "execution"
case identityLink = "identityLink"
case processDefinition = "processDefinition"
case processInstance = "processInstance"
case linksSelf = "self"
}
}

另外，如果你觉得懒惰你可以使用quicktype.io，因为nil是一个非常常见的解码响应，你可以扩展DataRequest来解析和获取请求中的值，就像使用responseDecodable一样，这里可以用这样的东西，

 extension DataRequest {
    fileprivate func decodableResponseSerializer<T: Decodable>() -> DataResponseSerializer<T> {
        return DataResponseSerializer { _, response, data, error in
            guard error == nil else { return .failure(error!) }

            guard let data = data else {
                return .failure(AFError.responseSerializationFailed(reason: .inputDataNil))
            }

            return Result { try newJSONDecoder().decode(T.self, from: data) }
        }
    }

    @discardableResult
    fileprivate func responseDecodable<T: Decodable>(queue: DispatchQueue? = nil, completionHandler: @escaping (DataResponse<T>) -> Void) -> Self {
        return response(queue: queue, responseSerializer: decodableResponseSerializer(), completionHandler: completionHandler)
    }
}

然后你可以这样称呼它

Alamofire.request(url, method:.post, parameters: parameters, headers: headers)
        .responseDecodable { (response: DataResponse< Task >) in completion(response.result) }

当你得到这样的东西时，它只会在你有不同类型的数据而不是你指定的数据时出现。

【讨论】：