斯威夫特3:

let jsonData = try? JSONSerialization.data(withJSONObject: dict, options: [])
let jsonString = String(data: jsonData!, encoding: .utf8)!
print(jsonString)

 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)
    }

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)
        }
    }
}

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")

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。

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)
        }