Swift之JSONEncoder和JSONDecoder

Swift 之 JSONEncoder 和 JSONDecoder

摘自官方文档&＃xff1a;

/// A type that can convert itself into and out of an external representation.
///
/// &＃96;Codable&＃96; is a type alias for the &＃96;Encodable&＃96; and &＃96;Decodable&＃96; protocols.
/// When you use &＃96;Codable&＃96; as a type or a generic constraint, it matches
/// any type that conforms to both protocols.
public typealias Codable &＃61; Decodable & Encodable


对象进行jsonEncode和jsonDecode

一个对象如果需要被编码/解码的话&＃xff0c;该对象所属的类需要遵循 Decodable & Encodable 协议。

以 Player 这类为例&＃xff0c;Player遵循了 Decodable 和 Encodable

import Foundationstruct Player: Codable {var name: Stringvar highScore: Int &＃61; 0var history: [Int] &＃61; []enum CodingKeys: String, CodingKey {case name &＃61; "Name"case highScore &＃61; "HighScore"case history &＃61; "History"}init(_ name: String) {self.name &＃61; name}
}//Codable, Equatable
extension Player {mutating func updateScore(_ newScore: Int) {history.append(newScore)if highScore < newScore {print("\(newScore)! A new high score for \(name)! &＃x1f389;")highScore &＃61; newScore}}
}


初始化一个Player对象&＃xff0c;并对其进行编码和解码&＃xff0c;看看编码和解码之后的数据

var jsonData: Data?// MARK: encode&＃xff08;编码&＃xff09;// Player对象
var player &＃61; Player("Tomas")
// 设置歌手分数
player.updateScore(50)
// 初始化一个encoder对象
let encoder &＃61; JSONEncoder()
do {// 将player对象encod&＃xff08;编码&＃xff09;let data: Data &＃61; try encoder.encode(player)// 打印print(data)print(String(data: data, encoding: String.Encoding.utf8) as Any)print(player)jsonData &＃61; data
} catch {}// MARK: decode&＃xff08;解码&＃xff09;
let decoder &＃61; JSONDecoder()
do {// 解码得到player对象let player: Player &＃61; try decoder.decode(Player.self, from: jsonData!)// 打印print(player)print(player.name)
} catch {}


一个对象被jsonEncode后&＃xff0c;对象将被转成 Data 类型的数据。
再将对象的 Data 数据通过jsonDecode&＃xff0c;可以还原原来的对象。

通过对对象的json编码和解码&＃xff0c;有助于我们理解数据在计算机中的存储。Data 其本质就是二进制流。

JSON字符串转模型

这是一个字符串

let jsonString: String &＃61; """
{"name" : "Tomas","highScore" : 50,"history" : [30, 40, 50]
}
"""


如何将其解析成player对象&＃xff1f;

// 将JSON字符串转成 Data
let jsonData: Data &＃61; jsonString.data(using: String.Encoding.utf8)!
// 将 data 转成对象
let decoder &＃61; JSONDecoder()
do {// 解码得到player对象let player: Player &＃61; try decoder.decode(Player.self, from: jsonData)// 打印print(player)print(player.name)
} catch {}


这种情况多用于客户端向服务端发送HTTP请求之后&＃xff0c;解析返回数据&＃xff0c;如果后台返回的是标准的JSON字符串的话直接这样解析就可以了。

JSONSerialization

Serialization 是序列化的意思&＃xff0c;JSONSerialization 顾名思义是对JSON进行序列化。

JSONSerialization 是对 JSON 字符串进行序列化和反序列化的工具类。用这个类可以将JSON转成对象&＃xff0c;也可以将对象转成JSON。

• objc 转 json

let dict: [String: Any] &＃61; ["name" : "Tomas","highScore" : 50,"history" : [30, 40, 50]
]
if JSONSerialization.isValidJSONObject(dict) &＃61;&＃61; false {return
}
// 将objc转成data
let data: Data &＃61; try! JSONSerialization.data(withJSONObject: dict, options: .fragmentsAllowed)
// 将data转成字符串输出
let string &＃61; String(data:data, encoding: String.Encoding.utf8)
print(string as Any)


打印结果&＃xff1a;

Optional("{\"history\":[30,40,50],\"name\":\"Tomas\",\"highScore\":50}")


这是一个标准的&＃xff0c;带转义的JSON字符串。也就是说我们将字典转成了JSON字符串。

• json 转 objc

let jsonString &＃61; "{\"history\":[30,40,50],\"name\":\"Tomas\",\"highScore\":50}"
let data &＃61; jsonString.data(using: String.Encoding.utf8)
let dict &＃61; try! JSONSerialization.jsonObject(with: data!, options: .allowFragments)
print(dict)


打印结果&＃xff1a;

{highScore &＃61; 50;history &＃61; (30,40,50);name &＃61; Tomas;
}


参考

[1] JSONEncoder文档&＃xff1a;https://developer.apple.com/documentation/foundation/jsonencoder/
[2] JSONDecoder文档&＃xff1a;https://developer.apple.com/documentation/foundation/jsondecoder
[3] JSONSerialization文档&＃xff1a;https://developer.apple.com/documentation/foundation/jsonserialization