JSONSerialization ReadingOptions

这两个值通常在序列化和反序列化时被使用，例如Data和JSON互转。先看一下他们各自有哪些选项可用。

extension JSONSerialization {

    
    @available(iOS 5.0, *)
    public struct ReadingOptions : OptionSet, @unchecked Sendable {

        public init(rawValue: UInt)

        
        public static var mutableContainers: JSONSerialization.ReadingOptions { get }

        public static var mutableLeaves: JSONSerialization.ReadingOptions { get }

        public static var fragmentsAllowed: JSONSerialization.ReadingOptions { get }

        
        @available(iOS 15.0, *)
        public static var json5Allowed: JSONSerialization.ReadingOptions { get }

        @available(iOS 15.0, *)
        public static var topLevelDictionaryAssumed: JSONSerialization.ReadingOptions { get }

        
        @available(iOS, introduced: 5.0, deprecated: 100000, renamed: "JSONSerialization.ReadingOptions.fragmentsAllowed")
        public static var allowFragments: JSONSerialization.ReadingOptions { get }
    }

    
    @available(iOS 5.0, *)
    public struct WritingOptions : OptionSet, @unchecked Sendable {

        public init(rawValue: UInt)

        
        public static var prettyPrinted: JSONSerialization.WritingOptions { get }

        
        /* Sorts dictionary keys for output using [NSLocale systemLocale]. Keys are compared using NSNumericSearch. The specific sorting method used is subject to change.
         */
        @available(iOS 11.0, *)
        public static var sortedKeys: JSONSerialization.WritingOptions { get }

        public static var fragmentsAllowed: JSONSerialization.WritingOptions { get }

        @available(iOS 13.0, *)
        public static var withoutEscapingSlashes: JSONSerialization.WritingOptions { get }
    }
}

上面是Xcode接口文档的描述。

ReadingOptions

使用场景
ReadingOptions的作用是用来反序列化Data时的参数

示例

let object: Any = try JSONSerialization.jsonObject(with: data, options: opt)

解释

• mutableContainers：得到一个可变的容器对象（Array, Dictionary）
• mutableLeaves：得到一个可变的叶子节点（JSON叶节点如果是String，按理会得到可变的String）
• fragmentsAllowed：除了Array，Dictionary以外，允许其他类型作为顶层，例如String、Number、Null、BooL（常用）
• json5Allowed：支持JSON5的语法#
• topLevelDictionaryAssumed：允许最外层没有括号包裹的JSON数据的解析
• allowFragments：会被废弃，建议fragmentsAllowed

WritingOptions

使用场景
WritingOptions的作用是用来序列化JSON时的参数

示例

let jsonObjc = JSONSerialization.data(withJSONObject: json, options: [])

解释

• prettyPrinted : 转换的JSON对象会通过换行和缩进，使JSON美观易读
• sortedKeys : 转换后的JSON对象会按照Key升序排序（内外层都排序）
• fragmentsAllowed : 允许除了Array、Dictionary的对象作为最外层
• withoutEscapingSlashes : 去除转换后JSON中的转移字符"/"

举例

• prettyPrinted

let json: [String: Any] = ["name": "tom", "address": ["province":"sh", "city":"sh"], "c":["c":"123","a":"321"]]
do {
  let jsonData = try JSONSerialization.data(withJSONObject: json, options: [.prettyPrinted])
  let jsonString = String.init(data: jsonData, encoding: String.Encoding.utf8)
  print(jsonString!) 
} catch { }

输出：
{
  "address" : {
    "province" : "sh",
    "city" : "sh"
  },
  "name" : "tom",
  "c" : {
    "c" : "123",
    "a" : "321"
  }
}

• sortedKeys
  内外层按照Key排序

let json: [String: Any] = ["name": "tom", "address": ["province":"sh", "city":"sh"], "c":["c":"123","a":"321"]]
do {
    let jsonData = try JSONSerialization.data(withJSONObject: json, options: [.sortedKeys,.prettyPrinted])
  let jsonString = String.init(data: jsonData, encoding: String.Encoding.utf8)
  print(jsonString!)

} catch { }

输出：
{
  "address" : {
    "city" : "sh",
    "province" : "sh"
  },
  "c" : {
    "a" : "321",
    "c" : "123"
  },
  "name" : "tom"
}

• fragmentsAllowed
  JSON最外层可以使用除Array、Dictionary的类型。 例如 Number、String、Bool、Null。否则默认只允许Dictionary、Array作为JSON最外层

let json = 123456
do {
    let jsonData = try JSONSerialization.data(withJSONObject: json, options: [.sortedKeys,.prettyPrinted])
  let jsonString = String.init(data: jsonData, encoding: String.Encoding.utf8)
  print(jsonString!)

} catch { }

输出：
123456

• withoutEscapingSlashes

struct User: Codable {
    let name: String
    let age: String
}

let user = User(username: "Tom", profileURL: "http://iqiyi.com")

let jsonEncoder = JSONEncoder()
jsonEncoder.outputFormatting = .withoutEscapingSlashes
let json = try? jsonEncoder.encode(user)

if let data = json, let str = String(data: data, encoding: .utf8) {
    print(str)
}


输出：
{"profileURL":"http://iqiyi.com","username":"Tom"}  // 这里没有转义字符