ios - 是否有可能有一个符合相同协议(protocol)的结构数组也支持 Codable？

Question

我已经设置了以下协议(protocol)，并且有 2 个结构，然后符合此协议(protocol):

protocol ExampleProtocol: Decodable {
    var name: String { get set }
    var length: Int { get set }
}

struct ExampleModel1: ExampleProtocol {
    var name: String
    var length: Int
    var otherData: Array<String>
}

struct ExampleModel2: ExampleProtocol {
    var name: String
    var length: Int
    var dateString: String
}

我想反序列化从服务器接收到的一些 JSON 数据，并且我知道它将在数组中返回 ExampleModel1 和 ExampleModel2 的混合:

struct ExampleNetworkResponse: Decodable {
    var someString: String
    var modelArray: Array<ExampleProtocol>
} 

无论如何使用 Codable 方法并轻松支持这两种模型？还是我需要手动反序列化每个模型的数据？

编辑1:

符合 Decodable 的结构，仍然给出相同的结果:

struct ExampleModel1: ExampleProtocol, Decodable {

    enum CodingKeys: String, CodingKey {
        case name, length, otherData
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        self.length = try container.decode(Int.self, forKey: .length)
        self.otherData = try container.decode(Array<String>.self, forKey: .otherData)
    }

    var name: String
    var length: Int
    var otherData: Array<String>
}

struct ExampleModel2: ExampleProtocol, Decodable {

    enum CodingKeys: String, CodingKey {
        case name, length, dateString
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        self.length = try container.decode(Int.self, forKey: .length)
        self.dateString = try container.decode(String.self, forKey: .dateString)
    }

    var name: String
    var length: Int
    var dateString: String
}

struct ExampleNetworkResponse: Decodable {
    var someString: String
    var modelArray: Array<ExampleProtocol>
}

Answer 1

如果您的ExampleProtocol数量有限s 并且你需要在同一个数组中有不同类型的 ExampleProtocols，那么你可以为 ExampleProtocol 创建一个持有者并将其用于解码/编码。

ExampleHolder 可以在一个数组中保存所有可能的 Decodable ExampleProtocol 类型。所以解码器 init 不需要有那么多 if-else 范围，并且将来更容易添加。

建议将 ExampleHolder 保留为私有(private)结构。所以不可能在文件之外访问它，甚至不能在 ExampleNetworkResponse 之外访问它。

enum ExampleNetworkResponseError: Error {
    case unsupportedExampleModelOnDecoding
}

private struct ExampleHolder: Decodable {
    let exampleModel: ExampleProtocol

    private let possibleModelTypes: [ExampleProtocol.Type] = [
        ExampleModel1.self,
        ExampleModel2.self
    ]

    init(from decoder: Decoder) throws {
        for type in possibleModelTypes {
            if let model = try? type.init(from: decoder) {
                exampleModel = model
                return
            }
        }

        throw ExampleNetworkResponseError.unsupportedExampleModelOnDecoding
    }
}

struct ExampleNetworkResponse: Decodable {
    var someString: String
    var modelArray: Array<ExampleProtocol>

    enum CodingKeys: String, CodingKey {
        case someString, modelArray
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        someString = try container.decode(String.self, forKey: .someString)
        let exampleHolderArray = try container.decode([ExampleHolder].self, forKey: .modelArray)
        modelArray = exampleHolderArray.map({ $0.exampleModel })
    }
}

––––––––––––––––––––––––––––––––––––––

如果在一个响应中只能有一种 ExampleProtocol然后在数组中:

struct ExampleNetworkResponse2<ModelArrayElement: ExampleProtocol>: Decodable {
    var someString: String
    var modelArray: Array<ModelArrayElement>
}

用法:

let decoder = JSONDecoder()
let response = try decoder.decode(
    ExampleNetworkResponse2<ExampleModel1>.self,
    from: dataToDecode
)