Swift 4 Codable Realm对象子类 [英] Swift 4 Codable Realm Object Subclasses

问题描述

试图将我的一些代码库切换到Swift 4的新的漂亮的Codable协议.我的设置如下所示:

trying to switch some of my codebase over to Swift 4's new nifty Codable protocol. My setup looks something like this:

class Base: Object, Codable {

    dynamic var id: String = ""
    dynamic var timestamp: String = ""

    private enum CodingKeys: String, CodingKey {

        case id = "_id"
        case timestamp = "timestamp"

    }

}

class User: Base {

    dynamic var name: String = ""

    private enum CodingKeys: String, CodingKey {
        case name = "name"
    }

    required init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        try super.init(from: decoder)

    }

}

我有一个符合Codable的基本领域对象类，还有一个Base的子类，它也有自己的编码键.我在User子类上重写init(decoder:)来映射我的其他编码键，然后调用super.init(decoder:)来映射Base的编码键.但是，一旦我覆盖init(decoder:)，就会出现以下错误:

I have a base realm object class that conforms to Codable, and a subclass of Base that also has it's own coding keys. I override init(decoder:) on the User subclass to map my additional coding keys, then call super.init(decoder:) to map Base's coding keys. However, once I override init(decoder:) I get the following errors:

• 必需的初始化程序"init()"必须由"Base"的子类提供
• 必需的初始值设定项'init(realm:schema :)'必须由'Base'的子类提供
• 必需的初始值设定项'init(value:schema :)'必须由'Base'的子类提供

• required initializer 'init()' must be provided by subclass of 'Base'
• required initializer 'init(realm:schema:)' must be provided by subclass of 'Base'
• required initializer 'init(value:schema:)' must be provided by subclass of 'Base'

我不确定要解决这些问题的正确方法.

I'm not sure what the correct way is to go about fixing these issues.

推荐答案

您不能覆盖init()或Realm Object的其他初始化程序.您可以改为使用便捷初始化程序.然后，您将无法调用super.init(from:)，因此请定义一个方法来解码超类的属性，例如Base.decode(from:).

You cannot override init() or other initializers of Realm Object. You can use convenience initializer instead. Then you cannot call super.init(from:), so define a method that decodes superclass' properties like Base.decode(from:).

请参见以下代码示例:

class Base: Object, Codable {
    dynamic var id: String = ""
    dynamic var timestamp: String = ""

    private enum CodingKeys: String, CodingKey {
        case id = "_id"
        case timestamp = "timestamp"
    }

    func decode(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.id = try container.decode(String.self, forKey: .id)
        self.timestamp = try container.decode(String.self, forKey: .timestamp)
    }
}

class User: Base {
    dynamic var name: String = ""

    private enum CodingKeys: String, CodingKey {
        case id = "_id"
        case timestamp
        case name = "name"
    }

    required convenience init(from decoder: Decoder) throws {
        self.init()

        try decode(from: decoder)

        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
    }
}

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