Dropdownlist in Gridview asp.net 2.0

hi seema,
I write some codes:

In Html Page:

<asp:gridview runat="server" id="GridView1" autogeneratecolumns="false" cellpadding="3" cellspacing="0" xmlns:asp="#unknown">
    <columns>
      <asp:templatefield headertext="Column1">
        <itemtemplate>
           <asp:dropdownlist runat="server" id="DropDownList1" width="150px/">
          <asp:hiddenfield runat="server" id="HiddenField1" value="<%#Bind("Column1") %"> />
        </asp:hiddenfield></asp:dropdownlist></itemtemplate>
      </asp:templatefield>
      <asp:boundfield datafield="Column2" headertext="Column2" />
      <asp:boundfield datafield="Column3" headertext="Column3" />
    </columns>
   </asp:gridview>

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindGridView();
            }
        }

        private void BindGridView()
        {
            DataTable datatable = new DataTable();
            datatable.Columns.Add("Column1", typeof(System.String));
            datatable.Columns.Add("Column2", typeof(System.String));
            datatable.Columns.Add("Column3", typeof(System.String));

            datatable.Rows.Add("1", "2", "3");
            datatable.Rows.Add("4", "5", "6");

            this.GridView1.DataSource = datatable;
            this.GridView1.DataBind();

            foreach (GridViewRow GridViewRow1 in this.GridView1.Rows)
            {
                //find hiddenField and DropDownList by id
                HiddenField hiddenField1 = (HiddenField)GridViewRow1.FindControl("HiddenField1");
                DropDownList dropDownList1 = (DropDownList)GridViewRow1.FindControl("DropDownList1");
                if (hiddenField1 != null && dropDownList1 != null)
                {
                    dropDownList1.Items.Clear;
                    //bind dropDownList1
                    //.....
                    dropDownList1.SelectedValue = hiddenField1.Value;
                }
            }
        }


Hope make you understand.

<asp:updatepanel xmlns:asp="#unknown" />