导出到Excel文件时，GridView导出不返回任何数据

由于某种原因，我在将GridView导出到Excel时遇到问题。我有两个按钮，一个是搜索，一旦用户提供了所需的信息，它就会处理搜索。另一个按钮是Export，它基本上处理将gridview导出到excel的操作。

我的问题是，当用户点击搜索按钮，然后他们想将数据导出到excel时，他们需要点击导出按钮。一切都很好，直到现在，当excel文件被查看时，没有数据被导出。这是我的两个按钮的代码：

任何帮助都将不胜感激，谢谢。

protected void search(object sender, EventArgs e)
{
    odbc.Open();
    ds = new DataSet();
    cmd = new OdbcCommand("SELECT XHLBCD AS LOCATION, XHLCST AS STATUS, XHEXUN AS EXCESS, XHSHUN AS SHORT, XHCNTD AS DATE_COUNTED FROM " +
                            "WM242BASD.XHCTRL00 WHERE XHCNTD BETWEEN '" + fromdate.Text + "' AND '" + todate.Text + "'", odbc);
    cmd.CommandType = CommandType.Text;
    cmd.Connection = odbc;
    oda = new OdbcDataAdapter(cmd);
    oda.Fill(ds);
    GridView1.DataSource = ds;
    GridView1.DataBind();
    odbc.Close();
}
protected void export_OnClick(object sender, EventArgs e)
{
    // Let's hide all unwanted stuffing
    GridView1.AllowPaging = false;
    GridView1.AllowSorting = false;
    // Let's bind data to GridView
    BindGrid();
    //Change the color back to white
    GridView1.HeaderRow.Style.Add("background-color", "#ffffff");
    //Apply color to the header
    GridView1.HeaderRow.Cells[0].Style.Add("background-color", "#e0e0e0");
    GridView1.HeaderRow.Cells[1].Style.Add("background-color", "#e0e0e0");
    GridView1.HeaderRow.Cells[2].Style.Add("background-color", "#e0e0e0");
    GridView1.HeaderRow.Cells[3].Style.Add("background-color", "#e0e0e0");
    GridView1.HeaderRow.Cells[4].Style.Add("background-color", "#e0e0e0");
    // Let's output the GridView
    Response.Clear();
    Response.ContentType = "application/vnd.xls";
    Response.AddHeader("content-disposition", "attachment;filename=" + reportid + ".xls");
    StringWriter swriter = new StringWriter();
    HtmlTextWriter hwriter = new HtmlTextWriter(swriter);
    GridView1.RenderControl(hwriter);

    Response.Write(swriter.ToString());
    Response.End();
}
private void BindGrid()
{
    GridView1.DataBind();
}