有时为了调试目的，有必要打印出服务器的响应。下面是我使用的函数:

extension Dictionary {

    var json: String {
        let invalidJson = "Not a valid JSON"
        do {
            let jsonData = try JSONSerialization.data(withJSONObject: self, options: .prettyPrinted)
            return String(bytes: jsonData, encoding: String.Encoding.utf8) ?? invalidJson
        } catch {
            return invalidJson
        }
    }

    func printJson() {
        print(json)
    }

}

使用示例:

(lldb) po dictionary.printJson()
{
  "InviteId" : 2,
  "EventId" : 13591,
  "Messages" : [
    {
      "SenderUserId" : 9514,
      "MessageText" : "test",
      "RecipientUserId" : 9470
    },
    {
      "SenderUserId" : 9514,
      "MessageText" : "test",
      "RecipientUserId" : 9470
    }
  ],
  "TargetUserId" : 9470,
  "InvitedUsers" : [
    9470
  ],
  "InvitingUserId" : 9514,
  "WillGo" : true,
  "DateCreated" : "2016-08-24 14:01:08 +00:00"
}

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"
}

 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)
    }

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)
        }

斯威夫特5:

extension Dictionary {
    
    /// Convert Dictionary to JSON string
    /// - Throws: exception if dictionary cannot be converted to JSON data or when data cannot be converted to UTF8 string
    /// - Returns: JSON string
    func toJson() throws -> String {
        let data = try JSONSerialization.data(withJSONObject: self)
        if let string = String(data: data, encoding: .utf8) {
            return string
        }
        throw NSError(domain: "Dictionary", code: 1, userInfo: ["message": "Data cannot be converted to .utf8 string"])
    }
}

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
    }

}