警告:将GridView导出到Excel文件

我有一个带有malty控件和网格视图的页面。

我想导出gridview数据到excel文件。我用这个类

public class GridViewExportUtil
{
public static void Export(string fileName, GridView gv)
{
    HttpContext.Current.Response.Clear();
    HttpContext.Current.Response.AddHeader(
        "content-disposition", string.Format("attachment; filename={0}", fileName));
    HttpContext.Current.Response.ContentType = "application/ms-excel";
    using (StringWriter sw = new StringWriter())
    {
        using (HtmlTextWriter htw = new HtmlTextWriter(sw))
        {
            //  Create a form to contain the grid
            Table table = new Table();
            //  add the header row to the table
            if (gv.HeaderRow != null)
            {
                GridViewExportUtil.PrepareControlForExport(gv.HeaderRow);
                table.Rows.Add(gv.HeaderRow);
            }
            //  add each of the data rows to the table
            foreach (GridViewRow row in gv.Rows)
            {
                GridViewExportUtil.PrepareControlForExport(row);
                table.Rows.Add(row);
            }
            //  add the footer row to the table
            if (gv.FooterRow != null)
            {
                GridViewExportUtil.PrepareControlForExport(gv.FooterRow);
                table.Rows.Add(gv.FooterRow);
            }
            //  render the table into the htmlwriter
            table.RenderControl(htw);
            //  render the htmlwriter into the response
            HttpContext.Current.Response.Write(sw.ToString());
            HttpContext.Current.Response.Flush();
            HttpContext.Current.Response.End();
        }
    }
}
/// <summary>
/// Replace any of the contained controls with literals
/// </summary>
/// <param name="control"></param>
private static void PrepareControlForExport(Control control)
{
    for (int i = 0; i < control.Controls.Count; i++)
    {
        Control current = control.Controls[i];
        if (current is LinkButton)
        {
            control.Controls.Remove(current);
            control.Controls.AddAt(i, new LiteralControl((current as LinkButton).Text));
        }
        else if (current is ImageButton)
        {
            control.Controls.Remove(current);
            control.Controls.AddAt(i, new LiteralControl((current as ImageButton).AlternateText));
        }
        else if (current is HyperLink)
        {
            control.Controls.Remove(current);
            control.Controls.AddAt(i, new LiteralControl((current as HyperLink).Text));
        }
        else if (current is DropDownList)
        {
            control.Controls.Remove(current);
            control.Controls.AddAt(i, new LiteralControl((current as DropDownList).SelectedItem.Text));
        }
        else if (current is CheckBox)
        {
            control.Controls.Remove(current);
            control.Controls.AddAt(i, new LiteralControl((current as CheckBox).Checked ? "True" : "False"));
        }
        if (current.HasControls())
        {
            GridViewExportUtil.PrepareControlForExport(current);
        }
    }
}

}

我的gridview有特殊的格式，我使用波斯语。

当我使用这个类时，它是导出gridview到excel，但是

我的问题是:当打开excel文件，我得到错误"是在一个不同的格式比指定的文件扩展名"。当打开文件时，波斯语文字难以辨认