hdf using

tb_preenddate.Text = DateTime.Now.ToString().Split(" ".ToCharArray())[0].ToString();

                            <asp:TemplateField HeaderText="司機">

                                <EditItemTemplate>

                                     <asp:DropDownList ID="DDLdriver" runat="server" Width="80px" />                             

                                      <asp:HiddenField ID="HDFdriver" runat="server" Value='<%# Eval("DRIVERNAME") %>'/> 

                                </EditItemTemplate>

                                <ItemTemplate>

                                    <asp:Label ID="Labeldriver" runat="server" Text='<%# Bind("DRIVERNAME") %>'></asp:Label>

                                </ItemTemplate>

                                <HeaderStyle HorizontalAlign="Center" Wrap="False" />

                                <ItemStyle HorizontalAlign="Center" Wrap="False" />

                            </asp:TemplateField>

                            <asp:BoundField DataField="DRIVERTELEPHONE" HeaderText="司機電話" ReadOnly="True">

                                <ItemStyle HorizontalAlign="Center" Wrap="False" />

                                <HeaderStyle HorizontalAlign="Center" Wrap="False" />

                            </asp:BoundField>

                            <asp:BoundField DataField="REQUESTDATE" HeaderText="日期" DataFormatString="{0:yyyy-MM-dd}" HtmlEncode="False" ReadOnly="True">

                                <ItemStyle HorizontalAlign="Center" Wrap="False" />

                                <HeaderStyle HorizontalAlign="Center" Wrap="False" />

                            </asp:BoundField>

        if (((DropDownList)e.Row.FindControl("DDL")) != null)

        {

            DropDownList ddlsub_flag = (DropDownList)e.Row.FindControl("DDL");

            ListItem a = new ListItem("2車輛", "2車輛");

            ListItem b = new ListItem("3車輛", "3車輛");

            ddlsub_flag.Items.Insert(0, a);

            ddlsub_flag.Items.Insert(1, b);

            ddlsub_flag.SelectedValue = ((HiddenField)e.Row.FindControl("HDF")).Value;

        }