37

我的数据结构有一个枚举作为键，我希望下面的内容能够自动解码。这是一个错误还是一些配置问题？

import Foundation

enum AnEnum: String, Codable {
  case enumValue
}

struct AStruct: Codable {
  let dictionary: [AnEnum: String]
}

let jsonDict = ["dictionary": ["enumValue": "someString"]]
let data = try! JSONSerialization.data(withJSONObject: jsonDict,     options: .prettyPrinted)
let decoder = JSONDecoder()
do {
  try decoder.decode(AStruct.self, from: data)
} catch {
  print(error)
}

我得到的错误是这个，似乎将字典与数组混淆了。

typeMismatch(Swift.Array, Swift.DecodingError.Context(codingPath: [Optional(__lldb_expr_85.AStruct.(CodingKeys in _0E2FD0A9B523101D0DCD67578F72D1DD).dictionary)], debugDescription: "预期解码 Array 但找到了字典。"))

4

3 回答 3

45

问题是Dictionary' 的Codable一致性目前只能正确处理String和Int键。对于任何其他Key类型的字典（其中/ ），Key它使用具有交替键值的无键容器（JSON 数组）进行编码和解码。EncodableDecodable

因此，在尝试解码 JSON 时：

{"dictionary": {"enumValue": "someString"}}

into AStruct，"dictionary"键的值应该是一个数组。

所以，

let jsonDict = ["dictionary": ["enumValue", "someString"]]

会工作，产生JSON：

{"dictionary": ["enumValue", "someString"]}

然后将其解码为：

AStruct(dictionary: [AnEnum.enumValue: "someString"])

但是，我真的认为Dictionary' 的Codable一致性应该能够正确处理任何CodingKey符合类型的类型Key（AnEnum可以）——因为它可以使用该键编码和解码到一个键控容器中（随时提交一个错误请求这个）。

在实现之前（如果有的话），我们总是可以构建一个包装器类型来做到这一点：

struct CodableDictionary<Key : Hashable, Value : Codable> : Codable where Key : CodingKey {

    let decoded: [Key: Value]

    init(_ decoded: [Key: Value]) {
        self.decoded = decoded
    }

    init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: Key.self)

        decoded = Dictionary(uniqueKeysWithValues:
            try container.allKeys.lazy.map {
                (key: $0, value: try container.decode(Value.self, forKey: $0))
            }
        )
    }

    func encode(to encoder: Encoder) throws {

        var container = encoder.container(keyedBy: Key.self)

        for (key, value) in decoded {
            try container.encode(value, forKey: key)
        }
    }
}

然后像这样实现：

enum AnEnum : String, CodingKey {
    case enumValue
}

struct AStruct: Codable {

    let dictionary: [AnEnum: String]

    private enum CodingKeys : CodingKey {
        case dictionary
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        dictionary = try container.decode(CodableDictionary.self, forKey: .dictionary).decoded
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(CodableDictionary(dictionary), forKey: .dictionary)
    }
}

（或者只是具有dictionarytype 的属性CodableDictionary<AnEnum, String>并使用自动生成的Codable一致性——然后就用 来说话dictionary.decoded）

现在我们可以按预期解码嵌套的 JSON 对象：

let data = """
{"dictionary": {"enumValue": "someString"}}
""".data(using: .utf8)!

let decoder = JSONDecoder()
do {
    let result = try decoder.decode(AStruct.self, from: data)
    print(result)
} catch {
    print(error)
}

// AStruct(dictionary: [AnEnum.enumValue: "someString"])

尽管说了这么多，但可以说，您使用带有 aenum作为键的字典所实现的只是struct带有可选属性的 a（如果您希望给定的值始终存在；使其成为非可选的）。

因此，您可能只希望您的模型看起来像：

struct BStruct : Codable {
    var enumValue: String?
}

struct AStruct: Codable {

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

    let bStruct: BStruct
}

这适用于您当前的 JSON：

let data = """
{"dictionary": {"enumValue": "someString"}}
""".data(using: .utf8)!

let decoder = JSONDecoder()
do {
    let result = try decoder.decode(AStruct.self, from: data)
    print(result)
} catch {
    print(error)
}

// AStruct(bStruct: BStruct(enumValue: Optional("someString")))
于 2017-06-23T16:30:27.280 回答
6

为了解决您的问题，您可以使用以下两个 Playground 代码片段之一。

#1。使用Decodable的init(from:)初始化程序

import Foundation

enum AnEnum: String, Codable {
    case enumValue
}

struct AStruct {
    enum CodingKeys: String, CodingKey {
        case dictionary
    }
    enum EnumKeys: String, CodingKey {
        case enumValue
    }

    let dictionary: [AnEnum: String]
}

extension AStruct: Decodable {

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let dictContainer = try container.nestedContainer(keyedBy: EnumKeys.self, forKey: .dictionary)

        var dictionary = [AnEnum: String]()
        for enumKey in dictContainer.allKeys {
            guard let anEnum = AnEnum(rawValue: enumKey.rawValue) else {
                let context = DecodingError.Context(codingPath: [], debugDescription: "Could not parse json key to an AnEnum object")
                throw DecodingError.dataCorrupted(context)
            }
            let value = try dictContainer.decode(String.self, forKey: enumKey)
            dictionary[anEnum] = value
        }
        self.dictionary = dictionary
    }

}

用法：

let jsonString = """
{
  "dictionary" : {
    "enumValue" : "someString"
  }
}
"""

let data = jsonString.data(using: String.Encoding.utf8)!
let decoder = JSONDecoder()
let aStruct = try! decoder.decode(AStruct.self, from: data)
dump(aStruct)

/*
 prints:
 ▿ __lldb_expr_148.AStruct
   ▿ dictionary: 1 key/value pair
     ▿ (2 elements)
       - key: __lldb_expr_148.AnEnum.enumValue
       - value: "someString"
 */

#2。使用KeyedDecodingContainerProtocol'sdecode(_:forKey:)方法

import Foundation

public enum AnEnum: String, Codable {
    case enumValue
}

struct AStruct: Decodable {
    enum CodingKeys: String, CodingKey {
        case dictionary
    }

    let dictionary: [AnEnum: String]
}

public extension KeyedDecodingContainer  {

    public func decode(_ type: [AnEnum: String].Type, forKey key: Key) throws -> [AnEnum: String] {
        let stringDictionary = try self.decode([String: String].self, forKey: key)
        var dictionary = [AnEnum: String]()

        for (key, value) in stringDictionary {
            guard let anEnum = AnEnum(rawValue: key) else {
                let context = DecodingError.Context(codingPath: codingPath, debugDescription: "Could not parse json key to an AnEnum object")
                throw DecodingError.dataCorrupted(context)
            }
            dictionary[anEnum] = value
        }

        return dictionary
    }

}

用法：

let jsonString = """
{
  "dictionary" : {
    "enumValue" : "someString"
  }
}
"""

let data = jsonString.data(using: String.Encoding.utf8)!
let decoder = JSONDecoder()
let aStruct = try! decoder.decode(AStruct.self, from: data)
dump(aStruct)

/*
 prints:
 ▿ __lldb_expr_148.AStruct
   ▿ dictionary: 1 key/value pair
     ▿ (2 elements)
       - key: __lldb_expr_148.AnEnum.enumValue
       - value: "someString"
 */
于 2017-07-13T10:21:38.727 回答
1

遵循 Imanou 的回答，并且超级通用。这将转换任何 RawRepresentable 枚举键控字典。可解码项目中不需要进一步的代码。

public extension KeyedDecodingContainer
{
    func decode<K, V, R>(_ type: [K:V].Type, forKey key: Key) throws -> [K:V]
        where K: RawRepresentable, K: Decodable, K.RawValue == R,
              V: Decodable,
              R: Decodable, R: Hashable
    {
        let rawDictionary = try self.decode([R: V].self, forKey: key)
        var dictionary = [K: V]()

        for (key, value) in rawDictionary {
            guard let enumKey = K(rawValue: key) else {
                throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: codingPath,
                     debugDescription: "Could not parse json key \(key) to a \(K.self) enum"))
            }
            
            dictionary[enumKey] = value
        }

        return dictionary
    }
}
于 2020-11-11T11:10:34.503 回答