请教一下导出Excel文档的问题.

1.下面的代码实现了单页导出Excel,我想实现当checkbox选中多少个就导出多少.
2.下面的RepExcelBind()方法里,导出前先让GridView1.AllowPaging = false;,但是导不出来数据,只有一对<div></div>在Excel里,这是什么原因?
    protected void btnExcel_Click(object sender, EventArgs e)
    {
        int intCount = 0;
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            CheckBox chk = (CheckBox)GridView1.Rows[i].FindControl("CheckBox1");
            if (chk.Checked)
            {
                intCount++;
            }
        }
        if (intCount == 0)
        {
            RepExcelBind();
        }
        else
        {
            Response.Write("<script>alert('这里根据勾选的行数导出..');</script>");
        }
    }    private void RepExcelBind()
    {
        //GridView1.AllowPaging = false;
        //GridView1.AllowSorting = false;
        //GridView1.DataBind();
        RepExcel();
        //GridView1.AllowPaging = true;
        //GridView1.AllowSorting = true;
        //GridView1.DataBind();
    }    private void RepExcel()
    {
        //string style = @"<style> .text { mso-number-format:yyyy/mm/dd; } </style>";
        Response.ClearContent();
        Response.AddHeader("content-disposition", "attachment;filename=MyExcelFile.xls");
        Response.ContentType = "application/excel";
        System.IO.StringWriter sw = new System.IO.StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        GridView1.RenderControl(htw);
        //Response.Write(style);
        Response.Write(sw.ToString());
        Response.End();
    }