我正在尝试通过 WCF 服务从 sql server 获取数据

Question

import UIKit

public struct student: Decodable {
    let id:Int
    let name:String
}

class ViewController: UIViewController {

    @IBAction func btnshow(_ sender: Any) {

        let link = "http://10.211.55.3/WcfService1/Service1.svc/GetData"
        guard let url = URL(string: link)else{
            print("error during connection")
            return
        }
        URLSession.shared.dataTask(with: url) { (data, response, error) in

            guard let data = data
                else{                    print("there is no data")
                return
            }
            do{
                let students = try JSONDecoder().decode(student.self, from: data)
                print(students)


            } catch{
                print("conversion error")
                print(error)
            }
        }.resume()            
    }
}

keyNotFound(CodingKeys(stringValue: "id", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "否 与键 CodingKeys 关联的值（stringValue: \"id\", intValue: nil) (\"id\").", 底层错误: nil))

Answer 1

嗯，打印出来的错误很容易解释。您获得的数据未按照您期望的方式进行格式化，并且缺少某些键（id 键），因此JSONDecoder() 无法对其进行解码。

在尝试解码之前确保您得到的响应格式正确。

编辑：所以在看到您的评论后，您的模型与您收到的 JSON 不匹配，应该是这样的：

import UIKit

public struct JsonStudent: Decodable {
    let students: [Student]

    enum CodingKeys: String, CodingKey {
        case students = "GetDataResult"
    }
}

public struct Student: Decodable {
    let id: Int
    let name: String
}

class ViewController: UIViewController {

    @IBAction func btnshow(_ sender: Any) {
        let link = "http://10.211.55.3/WcfService1/Service1.svc/GetData"

    guard let url = URL(string: link) else {
            print("error during connection")
            return
    }

    URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let data = data
                else {                    print("there is no data")
                return
            }
            do {
                let students = try JSONDecoder().decode(JsonStudent.self, from: data)
                print(students)
            } catch {
                print("conversion error")
                print(error)
            }
        }.resume()            
    }
}