在 Swift 中使用 Codable Protocol 解碼時如何區分？

Question

我正在使用 Swift 的 Codable 協議。 我已經分享了代碼。

我希望 Employee 類中的變量 boss 根據 Person 類中的 personType String 獲取類型。 我想使用 personType 作為鑒別器。 根據 personType 值，來自服務器的響應每次都會不同。

在 Employee 類中，我用 Person 類型聲明了 boss 變量。 如果 Person 類中的 personType 字符串是“Employee”，我希望它對 Employee 類型進行解碼，如果 personType 字符串是“Boss”，則對 Boss 類型進行解碼。 如果它為空，我只是想讓它解碼為 Person 類型。

任何幫助將非常感激。

public class Person: Codable {

    public let address: String
    public let age: Int
    public let name: String
    public let uid: String
    public let personType: String?

    private enum CodingKeys: String, CodingKey {
        case address
        case age
        case name
        case uid
        case personType
    }

    required public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        address = try container.decode(String.self, forKey: .address)
        age = try container.decode(Int.self, forKey: .age)
        name = try container.decode(String.self, forKey: .name)
        uid = try container.decode(String.self, forKey: .uid)
        personType = try container.decodeIfPresent(String.self, forKey: .personType)
    }
}


public class Employee: Person {

    public let department: String
    public let dependents: [Person]?
    public let salary: Int
    public let workingDays: [Days]
    public var boss: Person?

    private enum CodingKeys: String, CodingKey {
        case department
        case dependents
        case salary
        case workingDays
        case boss
    }


    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        department = try container.decode(String.self, forKey: .department)
        dependents = try container.decode([Person].self, forKey: .dependents)
        salary = try container.decode(Int.self, forKey: .salary)
        workingDays = try container.decode([Days].self, forKey: .workingDays)
        boss = try container.decode(Person.self, forKey: .boss)
        try super.init(from: decoder)
    }

}



public class Boss: Employee {
    let promotedAt: Double
    let assistant: Employee?

    enum CodingKeys: String, CodingKey {
        case promotedAt
        case assistant
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        promotedAt = try container.decode(Double.self, forKey: .promotedAt)
        assistant = try container.decodeIfPresent(Employee.self, forKey: .assistant)
        try super.init(from: decoder)
    }
}

例如，在以下響應中，在 boss 部分，personType 設置為“Boss”。 所以應該解碼為Boss類型。 如果是'Employee'，它應該自動解碼為Employee，或者如果它為null，則應該解碼為'Person'。

{ name: 'Shahid Khaliq',
  age: 5147483645,
  address: 'H # 531, S # 20',
  uid: '123321',
  salary: 20000,
  department: 'Software Development',
  workingDays: [ 'Monday', 'Tuesday', 'Friday' ],
  boss:
   { personType: 'Boss',
     assistant: null,
     name: 'Zeeshan Ejaz',
     age: 5147483645,
     address: 'H # 531, S # 20',
     uid: '123321',
     birthday: '1994-02-13',
     birthtime: '1994-02-13T14:01:54.000Z',
     salary: 20000,
     department: 'Software Development',
     joiningDay: 'Saturday',
     workingDays: [ 'Monday', 'Tuesday', 'Friday' ],
     dependents: null,
     hiredAt: 'Sun, 06 Nov 1994 08:49:37 GMT',
     boss: null,
     promotedAt: 1484719381 },
  dependents: null,
  hiredAt: 'Sun, 06 Nov 1994 08:49:37 GMT',
  personType: null }

Answer 1

需要根據您發布的當前回復更改模型

public class Employee: Person {

  public let department: String
  public let dependents: [Person]?
  public let salary: Int
  public let workingDays:[String] //[Days]
  public var boss: Person?

 private enum CodingKeys: String, CodingKey {
    case department
    case dependents
    case salary
    case workingDays
    case boss
 }


  required init(from decoder: Decoder) throws {
     let container = try decoder.container(keyedBy: CodingKeys.self)

     department = try container.decode(String.self, forKey: .department)
    //dependents = try container.decode([Person].self, forKey: .dependents)
    dependents = try container.decodeIfPresent([Person].self, forKey: .dependents)
    salary = try container.decode(Int.self, forKey: .salary)
    // workingDays = try container.decode([Days].self, forKey: .workingDays)
    workingDays = try container.decode([String].self, forKey: .workingDays)
   // boss = try container.decode(Person.self, forKey: .boss)
    boss = try container.decodeIfPresent(Person.self, forKey: .boss)
    try super.init(from: decoder)
 }
}

這里在幾個屬性中添加了decodeIfPresent ，因為它根據當前響應為空

在解碼時，您可以使用不同的東西，我使用 SwiftJSON 使代碼更具可讀性，

    // i have saved response in Response.JSON file so can change response as per need while testing below code.
    let file = Bundle.main.path(forResource: "Response", ofType: "JSON")
    let dataURL = URL(fileURLWithPath: file!)
    let data = try! Data(contentsOf: dataURL)
    let jsonData = try! JSON(data: data)
    //here JSON is struct which is part of SwiftyJSON

    print("jsondata \(jsonData)")
    do {

        let bossDict = jsonData["boss"]
        let dataBoss : Data = try! bossDict.rawData() 
        let bossType = bossDict["personType"].string
            if let type = bossType {
                if type == "Boss"{
                    let bossObj = try! JSONDecoder().decode(Boss.self, from: dataBoss)
                    print("boss name \(String(describing: bossObj.name))")
                    bossObj.listPropertiesWithValues()
                }else{
                    // type == "Employee"
                    let emplyeeObj = try! JSONDecoder().decode(Employee.self, from: dataBoss)
                    print("Employee name \(String(describing: emplyeeObj.name))")
                    emplyeeObj.listPropertiesWithValues()
                }
            }else{
                //type = nil

            }

    }catch{
        print("exception \(error)")
    }

您可以在鏈接DemoCodable下載相同的工作演示

Answer 2

我會在Employee類中的init(from decoder:)末尾添加一個 switch 語句

    switch personType {
    case "Boss":
         boss = try container.decode(Boss.self, forKey: .boss)
    case "Employee":
        boss = try container.decode(Employee.self, forKey: .boss)
    default:
        boss = nil
    }