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
    }

}

斯威夫特3.0

在Swift 3中，NSJSONSerialization的名字和它的方法已经改变了，根据Swift API设计指南。

let dic = ["2": "B", "1": "A", "3": "C"]

do {
    let jsonData = try JSONSerialization.data(withJSONObject: dic, options: .prettyPrinted)
    // here "jsonData" is the dictionary encoded in JSON data

    let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
    // here "decoded" is of type `Any`, decoded from JSON data

    // you can now cast it with the right type        
    if let dictFromJSON = decoded as? [String:String] {
        // use dictFromJSON
    }
} catch {
    print(error.localizedDescription)
}

快2.倍

do {
    let jsonData = try NSJSONSerialization.dataWithJSONObject(dic, options: NSJSONWritingOptions.PrettyPrinted)
    // here "jsonData" is the dictionary encoded in JSON data

    let decoded = try NSJSONSerialization.JSONObjectWithData(jsonData, options: [])
    // here "decoded" is of type `AnyObject`, decoded from JSON data

    // you can now cast it with the right type 
    if let dictFromJSON = decoded as? [String:String] {
        // use dictFromJSON
    }
} catch let error as NSError {
    print(error)
}

斯威夫特1

var error: NSError?
if let jsonData = NSJSONSerialization.dataWithJSONObject(dic, options: NSJSONWritingOptions.PrettyPrinted, error: &error) {
    if error != nil {
        println(error)
    } else {
        // here "jsonData" is the dictionary encoded in JSON data
    }
}

if let decoded = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as? [String:String] {
    if error != nil {
        println(error)
    } else {
        // here "decoded" is the dictionary decoded from JSON data
    }
}

斯威夫特5:

let dic = ["2": "B", "1": "A", "3": "C"]
let encoder = JSONEncoder()
if let jsonData = try? encoder.encode(dic) {
    if let jsonString = String(data: jsonData, encoding: .utf8) {
        print(jsonString)
    }
}

注意键和值必须实现Codable。字符串、整型和双精度(以及更多)已经是可编码的。参见编码和解码自定义类型。

还要注意，Any不符合Codable。这可能仍然是一个很好的方法来调整你的数据成为可编码的，这样你就可以使用Swift类型(特别是在你也要解码任何编码的json的情况下)，这样你就可以更声明你的编码的结果。

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")

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)
        }

 do{
        let dataDict = [ "level" :
                            [
                                ["column" : 0,"down" : 0,"left" : 0,"right" : 0,"row" : 0,"up" : 0],
                                ["column" : 1,"down" : 0,"left" : 0,"right" : 0,"row" : 0,"up" : 0],
                                ["column" : 2,"down" : 0,"left" : 0,"right" : 0,"row" : 0,"up" : 0],
                                ["column" : 0,"down" : 0,"left" : 0,"right" : 0,"row" : 1,"up" : 0],
                                ["column" : 1,"down" : 0,"left" : 0,"right" : 0,"row" : 1,"up" : 0],
                                ["column" : 2,"down" : 0,"left" : 0,"right" : 0,"row" : 1,"up" : 0]
                            ]
        ]
        var jsonData = try JSONSerialization.data(withJSONObject: dataDict, options: JSONSerialization.WritingOptions.prettyPrinted)
        let jsonStringData =  NSString(data: jsonData as Data, encoding: NSUTF8StringEncoding)! as String
        print(jsonStringData)
    }catch{
        print(error.localizedDescription)
    }