Swift/JSONEncoder：包含嵌套原始 JSON 对象文字的编码类

我在 Swift 中有一个类，其结构类似于：

class MyClass {
  var name: String
  var data: String
}

可以在哪里初始化data包含一个编码为字符串的 JSON 对象。

var instance = MyClass()
instance.name = "foo"
instance.data = "{\"bar\": \"baz\"}"

我现在想使用序列化这个实例JSONEncoder，我会得到与此类似的输出：

{
  "name": "foo",
  "data": "{\"bar\": \"baz\"}"
}

然而，我真正想要的是

{
  "name": "foo",
  "data": {
    "bar": "baz"
  }
}

我可以使用 JSONEncoder 实现此目的吗？ （不改变data打字远离String)

你首先需要解码data作为通用 JSON。这有点乏味，但并不是太难。看RNJSON https://github.com/rnapier/RNJSON/blob/main/Sources/RNJSON/RNJSON.swift对于我编写的版本，或者这是一个可以处理您的问题的精简版本。

enum JSON: Codable {
    struct Key: CodingKey, Hashable {
        let stringValue: String
        init(_ string: String) { self.stringValue = string }
        init?(stringValue: String) { self.init(stringValue) }
        var intValue: Int? { return nil }
        init?(intValue: Int) { return nil }
    }

    case string(String)
    case number(Double) // FIXME: Split Int and Double
    case object([Key: JSON])
    case array([JSON])
    case bool(Bool)
    case null

    init(from decoder: Decoder) throws {
        if let string = try? decoder.singleValueContainer().decode(String.self) { self = .string(string) }
        else if let number = try? decoder.singleValueContainer().decode(Double.self) { self = .number(number) }
        else if let object = try? decoder.container(keyedBy: Key.self) {
            var result: [Key: JSON] = [:]
            for key in object.allKeys {
                result[key] = (try? object.decode(JSON.self, forKey: key)) ?? .null
            }
            self = .object(result)
        }
        else if var array = try? decoder.unkeyedContainer() {
            var result: [JSON] = []
            for _ in 0..<(array.count ?? 0) {
                result.append(try array.decode(JSON.self))
            }
            self = .array(result)
        }
        else if let bool = try? decoder.singleValueContainer().decode(Bool.self) { self = .bool(bool) }
        else if let isNull = try? decoder.singleValueContainer().decodeNil(), isNull { self = .null }
        else { throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [],
                                                                       debugDescription: "Unknown JSON type")) }
    }

    func encode(to encoder: Encoder) throws {
        switch self {
        case .string(let string):
            var container = encoder.singleValueContainer()
            try container.encode(string)
        case .number(let number):
            var container = encoder.singleValueContainer()
            try container.encode(number)
        case .bool(let bool):
            var container = encoder.singleValueContainer()
            try container.encode(bool)
        case .object(let object):
            var container = encoder.container(keyedBy: Key.self)
            for (key, value) in object {
                try container.encode(value, forKey: key)
            }
        case .array(let array):
            var container = encoder.unkeyedContainer()
            for value in array {
                try container.encode(value)
            }
        case .null:
            var container = encoder.singleValueContainer()
            try container.encodeNil()
        }
    }
}

这样，您就可以解码 JSON，然后重新编码：

extension MyClass: Encodable {
    enum CodingKeys: CodingKey {
        case name, data
    }
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(name, forKey: .name)

        let json = try JSONDecoder().decode(JSON.self, from: Data(data.utf8))
        try container.encode(json, forKey: .data)
    }
}