如何在.net中实现文件下载

FileStream fs=new FileStream("d://11.xml",FileMode.Open);
// byte[] buffer=new byte[(int)fs.Length];
// fs.Read(buffer,0,(int)fs.Length);
// fs.Close ();
// // 下载文件
// Page.Response.AddHeader( "Content-Type", "application/octet-stream" );
// Response.Charset = "GB2312";
// Response.Buffer=true;
// HttpContext.Current.Response.AppendHeader("Content-Disposition","attachment;filename="+HttpUtility.UrlEncode(("11.xml")));
//// Response.OutputStream.Write(buffer,0,buffer.Length);
// Response.OutputStream.BeginWrite(buffer,0,buffer.Length,new AsyncCallback(this.MyCallBack),Response.OutputStream);

pCi=CommonFactory.CreateInstance(CommonData.sql);
// pCi.BeginTrans();
// pCi=CommonFactory.CreateInstance(CommonData.sql);
// pCi.Close();
// pCi.CommitTrans();
pCi=pCi=CommonFactory.CreateInstance(CommonData.sql);
pCi.Close();
pCi.Close();
pCi.Destory();





}
private void MyCallBack(IAsyncResult ar)
{
NetworkStream str=(NetworkStream)ar.AsyncState;
HttpContext.Current.Response.ClearHeaders();
str.EndWrite(ar);

}