Swift/JSONEncoder:编码 class 包含嵌套的原始 JSON 对象文字

Swift/JSONEncoder: Encoding class containing a nested raw JSON object literal

我在 Swift 中有一个 class,其结构类似于:

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

可以在 data 包含编码为字符串的 JSON 对象的地方进行初始化。

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

我现在想使用 JSONEncoder 序列化这个实例,我会得到类似于这样的输出:

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

不过,我真的很喜欢

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

我可以用 JSONEncoder 实现吗? (不改变 data 类型远离 String

你可以使用这样的东西:

extension MyClass {
    func jsonFormatted() throws -> String? {
        guard let data = data.data(using: .utf8) else {
            return nil
        }
        let anyData = try JSONSerialization.jsonObject(with: data, options: [])
        let dictionary = ["name": name, "data": anyData] as [String : Any]
        let jsonData = try JSONSerialization.data(withJSONObject: dictionary, options: .prettyPrinted)
        let jsonString = String(data: jsonData, encoding: .utf8)
        return jsonString
    }
}

所以基本上,您保留 data 的结构不变,但其余部分包含在一个字典中,可以转换为您想要实现的 json 字符串。
请注意,您需要处理可能抛出的可选和错误。 你可以用这个来测试:

if let jsonString = try? instance.jsonFormatted() {
    print(jsonString)
}

您首先需要将 data 解码为通用 JSON。这有点乏味,但并不太难。请参阅 RNJSON 了解我编写的版本,或者这里有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()
        }
    }
}

有了它,您可以解码 JSON 然后重新编码它:

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)
    }
}