如何在 Swift [45] 可解码协议中解码 JSON 字典类型的属性

问题描述

假设我有 Customer 数据类型，其中包含一个 metadata 属性，该属性可以包含客户对象中的任何 JSON 字典

Let's say I have Customer data type which contains a metadata property that can contains any JSON dictionary in the customer object

struct Customer {
  let id: String
  let email: String
  let metadata: [String: Any]
}

<小时>

{  
  "object": "customer",
  "id": "4yq6txdpfadhbaqnwp3",
  "email": "john.doe@example.com",
  "metadata": {
    "link_id": "linked-id",
    "buy_count": 4
  }
}

metadata 属性可以是任意 JSON 地图对象.

The metadata property can be any arbitrary JSON map object.

在我可以从 NSJSONDeserialization 的反序列化 JSON 中转换属性但使用新的 Swift 4 Decodable 协议之前，我仍然想不出办法做到这一点.

Before I can cast the property from a deserialized JSON from NSJSONDeserialization but with the new Swift 4 Decodable protocol, I still can't think of a way to do that.

有人知道如何在 Swift 4 中使用 Decodable 协议实现这一点吗?

Do anyone know how to achieve this in Swift 4 with Decodable protocol?

推荐答案

灵感来自 这个要点 我发现，我为 UnkeyedDecodingContainer 和 KeyedDecodingContainer 编写了一些扩展.您可以在此处找到我的要点的链接.通过使用此代码，您现在可以使用熟悉的语法解码任何 Array<Any> 或 Dictionary<String, Any>:

With some inspiration from this gist I found, I wrote some extensions for UnkeyedDecodingContainer and KeyedDecodingContainer. You can find a link to my gist here. By using this code you can now decode any Array<Any> or Dictionary<String, Any> with the familiar syntax:

let dictionary: [String: Any] = try container.decode([String: Any].self, forKey: key)

或

let array: [Any] = try container.decode([Any].self, forKey: key)

我发现有一个警告是解码字典数组[[String: Any]] 所需的语法如下.您可能希望抛出错误而不是强制转换:

there is one caveat I have found which is decoding an array of dictionaries [[String: Any]] The required syntax is as follows. You'll likely want to throw an error instead of force casting:

let items: [[String: Any]] = try container.decode(Array<Any>.self, forKey: .items) as! [[String: Any]]

编辑 2: 如果您只是想将整个文件转换为字典，则最好坚持使用 JSONSerialization 中的 api，因为我还没有找到扩展 JSONDecoder 本身以直接解码的方法一本字典.

EDIT 2: If you simply want to convert an entire file to a dictionary, you are better off sticking with api from JSONSerialization as I have not figured out a way to extend JSONDecoder itself to directly decode a dictionary.

guard let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] else {
  // appropriate error handling
  return
}

扩展

// Inspired by https://gist.github.com/mbuchetics/c9bc6c22033014aa0c550d3b4324411a

struct JSONCodingKeys: CodingKey {
    var stringValue: String

    init?(stringValue: String) {
        self.stringValue = stringValue
    }

    var intValue: Int?

    init?(intValue: Int) {
        self.init(stringValue: "(intValue)")
        self.intValue = intValue
    }
}


extension KeyedDecodingContainer {

    func decode(_ type: Dictionary<String, Any>.Type, forKey key: K) throws -> Dictionary<String, Any> {
        let container = try self.nestedContainer(keyedBy: JSONCodingKeys.self, forKey: key)
        return try container.decode(type)
    }

    func decodeIfPresent(_ type: Dictionary<String, Any>.Type, forKey key: K) throws -> Dictionary<String, Any>? {
        guard contains(key) else { 
            return nil
        }
        guard try decodeNil(forKey: key) == false else { 
            return nil 
        }
        return try decode(type, forKey: key)
    }

    func decode(_ type: Array<Any>.Type, forKey key: K) throws -> Array<Any> {
        var container = try self.nestedUnkeyedContainer(forKey: key)
        return try container.decode(type)
    }

    func decodeIfPresent(_ type: Array<Any>.Type, forKey key: K) throws -> Array<Any>? {
        guard contains(key) else {
            return nil
        }
        guard try decodeNil(forKey: key) == false else { 
            return nil 
        }
        return try decode(type, forKey: key)
    }

    func decode(_ type: Dictionary<String, Any>.Type) throws -> Dictionary<String, Any> {
        var dictionary = Dictionary<String, Any>()

        for key in allKeys {
            if let boolValue = try? decode(Bool.self, forKey: key) {
                dictionary[key.stringValue] = boolValue
            } else if let stringValue = try? decode(String.self, forKey: key) {
                dictionary[key.stringValue] = stringValue
            } else if let intValue = try? decode(Int.self, forKey: key) {
                dictionary[key.stringValue] = intValue
            } else if let doubleValue = try? decode(Double.self, forKey: key) {
                dictionary[key.stringValue] = doubleValue
            } else if let nestedDictionary = try? decode(Dictionary<String, Any>.self, forKey: key) {
                dictionary[key.stringValue] = nestedDictionary
            } else if let nestedArray = try? decode(Array<Any>.self, forKey: key) {
                dictionary[key.stringValue] = nestedArray
            }
        }
        return dictionary
    }
}

extension UnkeyedDecodingContainer {

    mutating func decode(_ type: Array<Any>.Type) throws -> Array<Any> {
        var array: [Any] = []
        while isAtEnd == false {
            // See if the current value in the JSON array is `null` first and prevent infite recursion with nested arrays.
            if try decodeNil() {
                continue
            } else if let value = try? decode(Bool.self) {
                array.append(value)
            } else if let value = try? decode(Double.self) {
                array.append(value)
            } else if let value = try? decode(String.self) {
                array.append(value)
            } else if let nestedDictionary = try? decode(Dictionary<String, Any>.self) {
                array.append(nestedDictionary)
            } else if let nestedArray = try? decode(Array<Any>.self) {
                array.append(nestedArray)
            }
        }
        return array
    }

    mutating func decode(_ type: Dictionary<String, Any>.Type) throws -> Dictionary<String, Any> {

        let nestedContainer = try self.nestedContainer(keyedBy: JSONCodingKeys.self)
        return try nestedContainer.decode(type)
    }
}

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