导出的excel文件保存为网页

当我通过c#代码编辑并保存导出的Excel文件时，它将保存为网页:

static String ISO_Date()
{
    return DateTime.Now.ToString("yyyy_MM_dd_HH_mm_ss");
}
protected void lnkbtnExport_Click(object sender, EventArgs e)
{
    if (grdView.Rows.Count > 0)
    {
        logger.logTrace("Exporting branch details to excel", Session["UserID"] == null ? 0 : Convert.ToInt32(Session["UserID"]));
        pBindData(null, true);
        grdView.DataSource = ViewState["DataBind"];
        grdView.DataBind();
        ExportGridView();
        pExportGridToExcel(grdView, "Location_Details_" + Convert.ToString(DateTime.Now) + ".xls");
    }
}
private void ExportGridView()
{
    System.IO.StringWriter sw = new System.IO.StringWriter();
    System.Web.UI.HtmlTextWriter htw = new System.Web.UI.HtmlTextWriter(sw);
    // Render grid view control.
    grdView.RenderControl(htw);
    // Write the rendered content to a file.
    string renderedGridView = sw.ToString();
    string path = System.Configuration.ConfigurationSettings.AppSettings["ExportedExcel"].ToString();
    if (!Directory.Exists(path))
    {
        Directory.CreateDirectory(path);
    }
    System.IO.File.WriteAllText(path + "_" + ISO_Date() + "_" + FromDate.Replace("/", "-") + "_" + ToDate.Replace("/", "-") + ".xls", renderedGridView);
}
private void pExportGridToExcel(GridView grdGridView, String fileName)
{
    Response.Clear();
    Response.AddHeader("content-disposition",
    String.Format("attachment;filename={0}", fileName));
    Response.Charset = "";
    Response.ContentType = "application/ms-excel";
    StringWriter stringWrite = new StringWriter();
    HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
    ClearControls(grdView);
    grdGridView.RenderControl(htmlWrite);
    Response.Write(stringWrite.ToString().Replace(HttpUtility.HtmlDecode(" "), " "));
    Response.End();
}

这些是我用来导出到excel的函数。它是导出但是当我打开同样的excel并尝试保存它时它保存为网页格式

 Response.Clear();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    using (StringWriter sw = new StringWriter())
    {
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        //To Export all pages
        GridView1.AllowPaging = false;
        this.BindGrid();
        GridView1.HeaderRow.BackColor = Color.White;
        foreach (TableCell cell in GridView1.HeaderRow.Cells)
        {
            cell.BackColor = GridView1.HeaderStyle.BackColor;
        }
        foreach (GridViewRow row in GridView1.Rows)
        {
            row.BackColor = Color.White;
            foreach (TableCell cell in row.Cells)
            {
                if (row.RowIndex % 2 == 0)
                {
                    cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
                }
                else
                {
                    cell.BackColor = GridView1.RowStyle.BackColor;
                }
                cell.CssClass = "textmode";
            }
        }
        GridView1.RenderControl(hw);
        //style to format numbers to string
        string style = @"<style> .textmode { } </style>";
        Response.Write(style);
        Response.Output.Write(sw.ToString());
        Response.Flush();
        Response.End();
    }