string qrcodeurl = "";

    string username = "";

    protected void btnSave_Click(object sender, EventArgs e)

    {

        //生成图片

        Bitmap image = Create_ImgCode(qrcodeurl, );

        //保存图片

        string server_saveurl = Server.MapPath("~/") + "Upload\\qrcode";

        SaveImg(server_saveurl, image);

        FileDownload(server_saveurl + "\\" + username + ".png");

    }

    /// <summary>

    /// 生成二维码图片

    /// </summary>

    /// <param name="codeNumber">要生成二维码的字符串</param>

    /// <param name="size">大小尺寸</param>

    /// <returns>二维码图片</returns>

    public Bitmap Create_ImgCode(string codeNumber, int size)

    {

        //创建二维码生成类

        QRCodeEncoder qrCodeEncoder = new QRCodeEncoder();

        //设置编码模式

        qrCodeEncoder.QRCodeEncodeMode = QRCodeEncoder.ENCODE_MODE.BYTE;

        //设置编码测量度

        qrCodeEncoder.QRCodeScale = size;

        //设置编码版本

        qrCodeEncoder.QRCodeVersion = ;

        //设置编码错误纠正

        qrCodeEncoder.QRCodeErrorCorrect = QRCodeEncoder.ERROR_CORRECTION.M;

        //生成二维码图片

        System.Drawing.Bitmap image = qrCodeEncoder.Encode(codeNumber);

        return image;

    } 

    /// <summary>

    /// 保存图片,在服务端

    /// </summary>

    /// <param name="strPath">保存路径</param>

    /// <param name="img">图片</param>

    public string SaveImg(string strPath, Bitmap img)

    {

        //保存图片到目录

        if (!Directory.Exists(strPath))

        {

            //当前目录不存在，则创建

            Directory.CreateDirectory(strPath);

        }

        //文件名称

        string filename = strPath + "/" + username + ".png";

        if (File.Exists(filename))

        {

            return filename;

        }

        img.Save(filename, System.Drawing.Imaging.ImageFormat.Png);

        return filename;

    }

    /// <summary>

    /// webform另存图片,在客户端

    /// </summary>

    /// <param name="FullFileName"></param>

    private void FileDownload(string FullFileName)

    {

        FileInfo DownloadFile = new FileInfo(FullFileName);

        Response.Clear();

        Response.ClearHeaders();

        Response.Buffer = false;

        Response.ContentType = "application/octet-stream";

        Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(DownloadFile.FullName, System.Text.Encoding.UTF8));

        Response.AppendHeader("Content-Length", DownloadFile.Length.ToString());

        Response.WriteFile(DownloadFile.FullName);

        Response.Flush();

        Response.End();

    }