SharePoint Attachement操作代码

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 SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    using (SPSite currentSite = new SPSite(SPContext.Current.Site.ID))
                    {
                        using (SPWeb web = currentSite.OpenWeb(SPContext.Current.Web.ID))
                        {
                            string filename = Request.QueryString["FileName"].ToString();
                            string ItemID = Request.QueryString["ID"].ToString();

                            web.AllowUnsafeUpdates = true;
                            string strContentType = "";

                            SPList list = web.Lists["TestList"];
                            SPFolder folder = web.Folders["Lists"].SubFolders["TestList"].SubFolders["Attachments"].SubFolders[ItemID.ToString()];

                            string url = folder.Url + "/" + filename.ToString();
                            SPFile tempFile = web.GetFile(url);
                            string[] file = filename.Split('.');
                            int a = file.Length;

                            //Get the extension of File.
                            byte[] obj = (byte[])tempFile.OpenBinary();

                            // Get the extension of File to determine the file type
                            string casestring = "";
                            casestring = file[a - 1].ToString();
                            switch (casestring)
                            {
                                case "txt":
                                    strContentType = "text/plain";
                                    break;
                                case "htm":
                                    strContentType = "text/html";
                                    break;
                                case "html":
                                    strContentType = "text/html";
                                    break;
                                case "rtf":
                                    strContentType = "text/richtext";
                                    break;
                                case "jpg":
                                    strContentType = "image/jpeg";
                                    break;

                                case "jpeg":
                                    strContentType = "image/jpeg";
                                    break;
                                case "gif":
                                    strContentType = "image/gif";
                                    break;
                                case "bmp":
                                    strContentType = "image/bmp";
                                    break;
                                case "mpg":
                                    strContentType = "video/mpeg";
                                    break;
                                case "mpeg":
                                    strContentType = "video/mpeg";
                                    break;
                                case "avi":
                                    strContentType = "video/avi";
                                    break;
                                case "pdf":
                                    strContentType = "application/pdf";
                                    break;
                                case "doc":
                                    strContentType = "application/msword";
                                    break;
                                case "dot":
                                    strContentType = "application/msword";
                                    break;
                                case "csv":
                                    strContentType = "application/vnd.msexcel";
                                    break;
                                case ".xls":
                                    strContentType = "application/vnd.msexcel";
                                    break;
                                case ".xlt":
                                    strContentType = "application/vnd.msexcel";
                                    break;
                                default:
                                    strContentType = "application/octet-stream";
                                    break;
                            }
                            Response.ClearContent();
                            Response.ClearHeaders();
                            Response.AppendHeader("Content-Disposition", "attachment; filename=" + filename.ToString());
                            Response.ContentType = strContentType;

                            //Check that the client is connected and has not closed the connection after the request
                            if (Response.IsClientConnected)
                            {
                                Response.BinaryWrite(obj);
                            }
                            Response.Flush();
                            Response.Close();
                        }
                    }
                });
            }
            catch (Exception ex)
            {

            }