具有继承的JSONEncoder

Question

我想在类播放器中使用JSONEncoder，它是在课后继承的。我得到错误“类型'Player.Type‘不能符合’可编码‘”。我找到了一些解决方案，但在这些情况下，JSON代码类似于使Person的变量类型。

人：

class Person: Codable {

    let name: String
    let surname: String
    let gender: Bool
    
    init(name: String, surname: String, gedner: Bool) throws {
        self.name = name
        self.surname = surname
        self.gender = gedner
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        name = try container.decode(String.self, forKey: .name)
        surname = try container.decode(String.self, forKey: .surname)
        gender = try container.decode(Bool.self, forKey: .gender)
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(self.name, forKey: .name)
        try container.encode(self.surname, forKey: .surname)
        try container.encode(self.gender, forKey: .gender)
    }
    
    private enum CodingKeys: String, CodingKey {
            case name
            case surname
            case gender
    }
}

播放器：

class Player: Person {
    private(set) var number: Int
    
    init(name: String, surname: String, gedner: Bool, number: Int) throws {
        self.number = number
        try super.init(name: name, surname: surname, gedner: gedner)
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.number = try container.decode(Int.self, forKey: .number)
        try super.init(from: decoder) 
    }
    
    override func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(number, forKey: .number)
        try container.encode(name, forKey: .name)
        try container.encode(surname, forKey: .surname)
        try container.encode(gender, forKey: .gender)
     
    }
    
    private enum CodingKeys: String, CodingKey {
        case number
        case name
        case surname
        case gender
    }
}

代码：

let newPlayer = try Player(name: "Name", surname: "Surname", gedner: true, number: 21)
let data = try encoder.encode(Player) //Error: Type 'Player.Type' cannot conform to 'Encodable'

Answer 1

为了澄清罗布说了些什么，再加上几个建议：

• 当解码时，需要提供一个类型。当编码时，需要提供一个对象：

let newPlayer = try Player(name: "Name", surname: "Surname", gedner: true, number: 21)

let encoder = JSONEncoder()
// Provide object
let data = try encoder.encode(newPlayer)

let decoder = JSONDecoder()
// Provide type (and data)
let decodedPlayer = try decoder.decode(Player.self, from: data)

• 如果事情像您在Person中描述的那样简单，那么Person不需要任何自定义编码/解码，您可以依赖于合成的编码/解码：

class Person: Codable {

    let name: String
    let surname: String
    let gender: Bool

    init(name: String, surname: String, gedner: Bool) throws {
        self.name = name
        self.surname = surname
        self.gender = gedner
    }
}

上述代码将生成与自定义代码相同的编码/解码。

• 用于子类，您总是需要指定自定义编码和解码，但只用于与父类不同的内容。例如，您不需要复制键，也不需要对其类进行编码。就像使用super.init一样，使用super.encode。所以代码变成：

class Player: Person {
    private(set) var number: Int

    init(name: String, surname: String, gedner: Bool, number: Int) throws {
        self.number = number
        try super.init(name: name, surname: surname, gedner: gedner)
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.number = try container.decode(Int.self, forKey: .number)
        try super.init(from: decoder)
    }

    override func encode(to encoder: Encoder) throws {
        try super.encode(to: encoder)
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(number, forKey: .number)
    }

    private enum CodingKeys: String, CodingKey {
        case number
    }
}

与编码/解码无关

如评论中提到的@LeoDabus所述，Player.init(name: String...中的

• 看起来不像您的init在Person中会抛出任何异常，因此您可能希望从Person.init和throws中删除throws

您还可能希望将参数名从gender更正为

class Person: Codable {

    let name: String
    let surname: String
    let gender: Bool

    init(name: String, surname: String, gender: Bool) {
        self.name = name
        self.surname = surname
        self.gender = gender
    }
}

和

class Player: Person {
    private(set) var number: Int

    init(name: String, surname: String, gender: Bool, number: Int) {
        self.number = number
        super.init(name: name, surname: surname, gender: gender)
    }
    // ...