set your Rakefile

  app.pods do
    pod 'AFNetworking'
    ...
  end

  def downloadFile(url, file, filesize)
    url = NSURL.URLWithString(url)
    request = NSURLRequest.requestWithURL(url)
    operation = AFHTTPRequestOperation.alloc.initWithRequest(request)
    operation.outputStream = NSOutputStream.outputStreamToFileAtPath(file, append: false)

    unless filesize.nil?
      SVProgressHUD.showProgress(0, status: "Downloading file")
      operation.setDownloadProgressBlock(lambda{|bytesRead, totalBytesRead, totalBytesExpected|
        SVProgressHUD.showProgress((((totalBytesRead/filesize.to_f)*100.0).round)/100.0, status: "Downloading file")
      })
    end

    operation.setCompletionBlockWithSuccess(lambda{|request, response|
      SVProgressHUD.dismiss unless filesize.nil?
    }, failure: lambda{|request, err|
      SVProgressHUD.dismiss unless filesize.nil?

      @alert = UIAlertView.alloc.initWithTitle('Error',
          message: 'Error when downloading data.', delegate: nil, cancelButtonTitle: 'OK',
          otherButtonTitles: nil)
      @alert.show
    })
    operation.start
  end

when downloading multiple files, use NSOperationQueue

# change donwloadFile

def downloadFile..
 ...
 operation # was operation.start
end

@queue = NSOperationQueue.alloc.init
@queue.name = "FileDownload"
@queue.maxConcurrentOperationCount = 1   # number of concurrent downloads

@queue.addOperation(downloadFile(url, file, filesize))