[英]Subclassing swift generic decodable type
編輯:正如Rob Napier 所寫,問題存在於 Xcode 9.2 中。 在 Xcode 9.3 中,該問題不再相關。
我的服務器 json 響應都打包在data
對象中:
{
"data": {...}
}
所以我有以下通用類型來解析 JSON:
class DataContainer<T: Decodable>: Decodable {
let data: T
init(data: T)
self.data = data
}
}
大多數情況下它工作正常,但有一個響應,我還需要解析included
字段,因此我創建了SpecificDataContainer
子類:
class SpecificDataContainer: DataContainer<DataObject> {
let included: [IncludedObject]
init() {
included = []
super.init(data: DataObject(id: ""))
}
}
上面的實現給了我編譯器錯誤'required' initializer 'init(from:)' must be provided by subclass of 'DataContainer'
。
我在SpecificDataContainer
實現了init(from:)
但編譯器仍然給我同樣的錯誤。
似乎我在這里錯過了一些明顯的東西。 我做錯了什么? 這是我的完整代碼:
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!")
}
出於某種原因,Xcode 無法識別Codable
子類中自動生成的init(from:)
(正如 Rob 所說,這可能是一個錯誤)。 在 Xcode 9.3 發布之前,您還可以通過將初始化程序添加到基類來解決此問題:
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)
}
這似乎是 Xcode 9.2 中的一個錯誤。 在 9.3b4 中,您的代碼很好。
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