子类化 swift 泛型可解码类型

Question

编辑： 作为，问题存在于Xcode 9.2。在 Xcode 9.3 中，该问题不再相关。

我的服务器 json 响应全部打包在 data 对象中：

{ 
    "data": {...}
}

所以我有以下通用类型来解析 JSON:

class DataContainer<T: Decodable>: Decodable {

    let data: T

    init(data: T)
        self.data = data
    }
}

大多数时候它工作正常，但有一个响应我还需要解析 included 字段所以我创建了 SpecificDataContainer 子类：

class SpecificDataContainer: DataContainer<DataObject> {
    let included: [IncludedObject]

    init() {
        included = []
        super.init(data: DataObject(id: ""))
    }
}

上面的实现给我编译器错误 'required' initializer 'init(from:)' must be provided by subclass of 'DataContainer'。

我在 SpecificDataContainer 中实现了 init(from:)，但编译器仍然给我同样的错误。

看来我在这里漏掉了一些明显的东西。我究竟做错了什么？这是我的完整代码：

import Foundation

let jsonData = """
{
    "data": {
        "id": "some_id"
    },
    "included": [
        {
            "id": "some_id2"
        }
    ]
}
""".data(using:.utf8)!

struct DataObject: Decodable {
    let id: String
}

struct IncludedObject: Decodable {
    let id: String
}

class DataContainer<T: Decodable>: Decodable {
    let data: T

    init(data: T) {
        self.data = data
    }
}

class SpecificDataContainer: DataContainer<DataObject> {
    let included: [IncludedObject]

    init() {
        included = []
        super.init(data: DataObject(id: ""))
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        var includedArray = try container.nestedUnkeyedContainer(forKey: .included)

        var includedObjects:[IncludedObject] = []
        while !includedArray.isAtEnd {
            let includedObject = try includedArray.decode(IncludedObject.self)
            includedObjects.append(includedObject)
        }
        self.included = includedObjects

        try super.init(from: decoder)
    }

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

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
if let obj = try? decoder.decode(SpecificDataContainer.self, from: jsonData) {
    print("object id \(obj.data.id)")
} else {
    print("Fail!")
}

Answer 1

这似乎是 Xcode 9.2 中的错误。在 9.3b4 中你的代码没问题。

Answer 2

出于某种原因 Xcode 无法识别 Codable 的子 class 中的 auto-generated init(from:)（正如 Rob 所说，它可能是漏洞）。在 Xcode 9.3 发布之前，您可以通过将初始化器添加到基础 class 来解决此问题：

class DataContainer<T: Decodable>: Decodable {    
    let data: T

    enum CodingKeys: String, CodingKey {
        case data
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        data = try container.decode(T.self, forKey: .data)
    }

子类化 swift 泛型可解码类型

Subclassing swift generic decodable type

ios

json

swift

decodable