swift中JSONSerialization的ReadingO

swift中解析、创建json数据需要用到下面两个参数，下面是这些参数的一些解释

extension JSONSerialization {

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

        public init(rawValue: UInt)

        public static var mutableContainers: JSONSerialization.ReadingOptions { get }

        public static var mutableLeaves: JSONSerialization.ReadingOptions { get }

        public static var allowFragments: JSONSerialization.ReadingOptions { get }
    }

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

        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 }
    }
}

一、ReadingOptions

1、mutableContainer
允许将数据解析成json对象后，修改其中的数据

var jsonString:NSString = "{\"names\":[\"James\",\"Jobs\",\"Tom\"]}" as NSString
let jsonData = jsonString.dataUsingEncoding(NSUTF8StringEncoding)

if let jsonObj:NSDictionary = NSJSONSerialization.JSONObjectWithData(jsonData!, options: NSJSONReadingOptions.MutableContainers, error: nil) as? NSDictionary {
    //操作之前
    print(jsonObj) //James, Jobs, Tom
    if let nameArray:NSMutableArray = jsonObj["names"] as? NSMutableArray {
        nameArray.addObject("Cook")
    }
    //操作之后
    print(jsonObj) //James, Jobs, Tom, Cook
}

2、mutableLeaves
使解析出来的json对象的叶子节点的属性变为NSMutableString

3、allowFragments
这个参数平常用的比较多，他允许被解析的json数据不是array或者dic包裹，可以是单个string值

var jsonFragmentString = "\"something wrong about api\"" as NSString

let jsonFragmentData = jsonFragmentString.dataUsingEncoding(NSUTF8StringEncoding)

if let jsonObj: AnyObject = NSJSONSerialization.JSONObjectWithData(jsonFragmentData!, options: .AllowFragments, error: nil) {

    //使用 AllowFragments 选项，解析成功。
    print(jsonObj)

}

二、WritingOptions

1、prettyPrinted
或许的json数据有良好的格式化，方便阅读，对比如下

  let jsonObj: [String: Any] = ["name": "xiaoxin", "address": ["province: test", "city: test"]]
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: jsonObj, options: JSONSerialization.WritingOptions.prettyPrinted)
        
        let jsonString = String.init(data: jsonData, encoding: String.Encoding.utf8)
        print(jsonString!)
        
    } catch {
        print(error)
    }
    
    do {
        let jsonData2 = try JSONSerialization.data(withJSONObject: jsonObj, options: [])
        
        let jsonString1 = String.init(data: jsonData2, encoding: String.Encoding.utf8)
        print(jsonString1!)
        
    } catch {
        print(error)
    }

结果：

{
  "name" : "xiaoxin",
  "address" : [
    "province: test",
    "city: test"
  ]
}
{"name":"xiaoxin","address":["province: test","city: test"]}

2、sortedKeys
改选项只有iOS11才提供，按照文档描述，使用该选项会对字典中的keys进行排序

  let jsonObj: [String: Any] = ["a": "xiaoxin", "x": ["3": "3test", "2": "2test", "5": "5test"], "d": "dtest" ]
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: jsonObj, options: JSONSerialization.WritingOptions.prettyPrinted)
        
        let jsonString = String.init(data: jsonData, encoding: String.Encoding.utf8)
        print(jsonString!)
        
    } catch {
        print(error)
    }
    
    do {
        let jsonData2 = try JSONSerialization.data(withJSONObject: jsonObj,
                                                   options: [JSONSerialization.WritingOptions.prettyPrinted,
                                                             JSONSerialization.WritingOptions.sortedKeys])
        
        let jsonString1 = String.init(data: jsonData2, encoding: String.Encoding.utf8)
        print(jsonString1!)
        
    } catch {
        print(error)
    }

结果如下：

{
  "d" : "dtest",
  "a" : "xiaoxin",
  "x" : {
    "5" : "5test",
    "2" : "2test",
    "3" : "3test"
  }
}
{
  "a" : "xiaoxin",
  "d" : "dtest",
  "x" : {
    "2" : "2test",
    "3" : "3test",
    "5" : "5test"
  }
}

参考：
1、Swift 与 JSON 数据