c#断点续传

今天写断点续传
if (IStartPos > 0)
{
request.AddRange((int)IStartPos);
}
ns = request.GetResponse().GetResponseStream();
downloadThread = new Thread(new ThreadStart(downloadFile));
//fs = new FileStream(StrFileName, FileMode.OpenOrCreate, FileAccess.Write);
downloadThread.Start();

private void downloadFile()
{
//if (IStartPos > 0)
//{
// request.AddRange((int)IStartPos);
//}
//ns = request.GetResponse().GetResponseStream();

int i = ns.Read(buffer, 0, buffer.Length);
UIDel = new updateData(updateUI);
while (i > 0)
{

downlength += i;
string value = downlength.ToString();