Question

编辑：作为Rob Napier wrote，Xcode 9.2中存在问题。在Xcode 9.3中，问题已不再适用。

我的服务器json响应全部打包在data对象中：

{ 
    "data": {...}
}

所以我有以下泛型类型来解析JSON：

class DataContainer<T: Decodable>: Decodable {

    let data: T

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

大部分时间它工作正常，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: ""))
    }
}

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

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

我似乎错过了一些明显的东西。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

由于某些原因，Xcode无法识别init(from:)子类中自动生成的Codable（因为Rob说它可能是一个错误）。在Xcode 9.3发布之前，您可以通过将初始化程序添加到基类来解决此问题：

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)
}

Answer 2

这似乎是Xcode 9.2中的一个错误。在9.3b4你的代码很好。

子类化swift通用可解码类型

2 个答案: