我想获取FTP上文件的大小。//GetFileSizereqSize=(FtpWebRequest)FtpWebRequest.Create(newUri(FtpPath+filePath));reqSize.Credentials=newNetworkCredential(Username,Password);reqSize.Method=WebRequestMethods.Ftp.GetFileSize;reqSize.UseBinary=true;FtpWebResponserespSize=(FtpWebResponse)reqSize.GetResponse();longsi