help displaying the alert!!

import Foundation
import UIKit

class networkOperation{

   lazy  var config:NSURLSessionConfiguration = NSURLSessionConfiguration.defaultSessionConfiguration()
   lazy var session:NSURLSession = NSURLSession(configuration:self.config)

    typealias JSONDictionaryCompletion = ([String:AnyObject]->Void)

    let queryURL:NSURL

    init(url:NSURL){
    self.queryURL = url

    }



    func downloadJSONfromURL(completion:JSONDictionaryCompletion){
     let request = NSURLRequest(URL: queryURL) 
        let dataTask = session.dataTaskWithRequest(request) {
        (let data,let response, let error) in
            // HTTP response eh uma reposta do servidor ao cliente quando recebe uma HTTP request.The response contains info about the date,size of the request and other things like the status code
//1:check HTTP response for sucessful GET request
            if let httpResponse = response as? NSHTTPURLResponse{//casting pq NSHTTPPURLResponse tem method para os status code
                switch(httpResponse.statusCode){
                case 200:
                 //Create JSON object with data
                    let JSONDictionary = try!NSJSONSerialization.JSONObjectWithData(data!, options:  NSJSONReadingOptions()) as! [String:AnyObject]
                        completion(JSONDictionary)

                    //NSJSONSerialization->usada para converter JSON para foundation objects e foundation objects para JSON objects

                case 400:
            print("probably mispelled, please try again")

                default:
                print("bad request")

                }}
                else{
                print("ERROR!!!!not valid http response")
                self.creatingAnAlert{
                (let errorAlert) in
            let viewController = ViewController()
                    errorAlert.addAction(UIAlertAction(title: "retry", style: UIAlertActionStyle.Default, handler: //retry loading the weather data))
                    viewController.presentViewController(errorAlert, animated: true, completion: nil)
                }
            }

            }

    dataTask.resume()

    }
    func creatingAnAlert(handler: (UIAlertController)->Void){
        let alert = UIAlertController(title: "Alert", message: "error", preferredStyle: .Alert)
       alert.addAction(UIAlertAction(title: "ok", style: UIAlertActionStyle.Default, handler: nil))
        handler(alert)
    }
}