private void StartUpload(FileInfo file)
{
_uploadedFile = file;
_fileStream = _uploadedFile.OpenRead();
_dataLength = _fileStream.Length;
var pathofAttachment = AttachmentPath.Split('/').LastOrDefault();
var dataToSend = _dataLength - _dataSent;
var isLastChunk = dataToSend <= ChunkSize;
var isFirstChunk = _dataSent == 0;
var httpHandlerUrlBuilder = new UriBuilder(string.Format("{0}/FileUpload.ashx", _baseUri));
httpHandlerUrlBuilder.Query = string.Format("{4}file={0}&offset={1}&last={2}&first={3}&Folder={5}",
pathofAttachment, _dataSent, isLastChunk, isFirstChunk,
string.IsNullOrEmpty(httpHandlerUrlBuilder.Query) ? "" : httpHandlerUrlBuilder.Query.Remove(0, 1) + "&", FolderPath);
var webRequest = (HttpWebRequest)WebRequest.Create(httpHandlerUrlBuilder.Uri);
webRequest.Method = "POST";
webRequest.BeginGetRequestStream(WriteToStreamCallback, webRequest);
}