如何在.net中實現檔案下載

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 ();
//        // 下載檔案
//   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);

  }