这是一个简单的扩展来做到这一点:

https://gist.github.com/stevenojo/0cb8afcba721838b8dcb115b846727c3

extension Dictionary {
    func jsonString() -> NSString? {
        let jsonData = try? JSONSerialization.data(withJSONObject: self, options: [])
        guard jsonData != nil else {return nil}
        let jsonString = String(data: jsonData!, encoding: .utf8)
        guard jsonString != nil else {return nil}
        return jsonString! as NSString
    }

}

我对你的问题的回答如下

let dict = ["0": "ArrayObjectOne", "1": "ArrayObjecttwo", "2": "ArrayObjectThree"]

var error : NSError?

let jsonData = try! NSJSONSerialization.dataWithJSONObject(dict, options: NSJSONWritingOptions.PrettyPrinted)

let jsonString = NSString(data: jsonData, encoding: String.Encoding.utf8.rawValue)! as String

print(jsonString)

答案是

{
  "0" : "ArrayObjectOne",
  "1" : "ArrayObjecttwo",
  "2" : "ArrayObjectThree"
}

你问题的答案如下:

斯威夫特2.1

     do {
          if let postData : NSData = try NSJSONSerialization.dataWithJSONObject(dictDataToBeConverted, options: NSJSONWritingOptions.PrettyPrinted){

          let json = NSString(data: postData, encoding: NSUTF8StringEncoding)! as String
          print(json)}

        }
        catch {
           print(error)
        }

2022年，swift 5

扩展的使用:

编码:

if let json = statisticsDict.asJSONStr() {
     //your action with json
}

从字典解码:

json.decodeFromJson(type: [String:AppStat].self)
    .onSuccess{
        $0// your dictionary of type: [String:AppStat]
    }

扩展:

extension Dictionary where Key: Encodable, Value: Encodable {
    func asJSONStr() -> String? {
        let encoder = JSONEncoder()
        if let jsonData = try? encoder.encode(self) {
            if let jsonString = String(data: jsonData, encoding: .utf8) {
                return jsonString
            }
        }
        
        return nil
    }
}

public extension String {
    func decodeFromJson<T>(type: T.Type) -> Result<T, Error> where T: Decodable {
        self.asData()
            .flatMap { JSONDecoder().try(type, from: $0) }
    }

    func asData() -> Result<Data, Error> {
        if let data = self.data(using: .utf8) {
            return .success(data)
        } else {
            return .failure(WTF("can't convert string to data: \(self)"))
        }
    }
}

extension JSONDecoder {
    func `try`<T: Decodable>(_ t: T.Type, from data: Data) -> Result<T,Error> {
        do {
            return .success(try self.decode(t, from: data))
        } catch {
            return .failure(error)
        }
    }
}

你的假设是错误的。只是因为调试器/Playground用方括号显示你的字典(这是Cocoa显示字典的方式)，这并不意味着这是JSON输出格式化的方式。

下面是将字符串字典转换为JSON的示例代码:

Swift 3版本:

import Foundation

let dictionary = ["aKey": "aValue", "anotherKey": "anotherValue"]
if let theJSONData = try? JSONSerialization.data(
    withJSONObject: dictionary,
    options: []) {
    let theJSONText = String(data: theJSONData,
                               encoding: .ascii)
    print("JSON string = \(theJSONText!)")
}

要以“漂亮打印”的格式显示上面的内容，你可以将选项行更改为:

    options: [.prettyPrinted]

或者在Swift 2语法中:

import Foundation
 
let dictionary = ["aKey": "aValue", "anotherKey": "anotherValue"]
let theJSONData = NSJSONSerialization.dataWithJSONObject(
  dictionary ,
  options: NSJSONWritingOptions(0),
  error: nil)
let theJSONText = NSString(data: theJSONData!,
  encoding: NSASCIIStringEncoding)
println("JSON string = \(theJSONText!)")

它的输出是

"JSON string = {"anotherKey":"anotherValue","aKey":"aValue"}"

或者用漂亮的格式:

{
  "anotherKey" : "anotherValue",
  "aKey" : "aValue"
}

正如您所期望的那样，在JSON输出中，字典用花括号括起来。

编辑:

在Swift 3/4语法中，上面的代码看起来像这样:

  let dictionary = ["aKey": "aValue", "anotherKey": "anotherValue"]
    if let theJSONData = try?  JSONSerialization.data(
      withJSONObject: dictionary,
      options: .prettyPrinted
      ),
      let theJSONText = String(data: theJSONData,
                               encoding: String.Encoding.ascii) {
          print("JSON string = \n\(theJSONText)")
    }
  }

这对我来说很管用:

import SwiftyJSON

extension JSON {
    
    mutating func appendIfKeyValuePair(key: String, value: Any){
        if var dict = self.dictionaryObject {
            dict[key] = value
            self = JSON(dict)
        }
    }
}

用法:

var data: JSON = []

data.appendIfKeyValuePair(key: "myKey", value: "myValue")