bind dropdownlist from database

HI

I have dropdownlists in register.aspx page

1- ddlzoneE 2-DdlDistrictE

I bind them from database

and when I select item from ddlzoneE ,  ddlDistrictE's Item change below are code

 protected void DDLzoneE_SelectedIndexChanged(object sender, EventArgs e)
    {
        BindDistrictE();

    }
    private void BindDistrictE()
    {
        DdlDistrictE.Items.Clear();
        DdlDistrictE.Items.Add(new ListItem("ALL", ""));
        DdlDistrictE.AppendDataBoundItems = true;

        SqlCommand _cmd = new SqlCommand("selectdistrict", _cn);
        _cmd.CommandType = CommandType.StoredProcedure;
        _cmd.Parameters.AddWithValue("@RegionID", ddlzoneE.SelectedItem.Text);

        _cn.Open();
        DdlDistrictE.DataSource = _cmd.ExecuteReader();
        DdlDistrictE.DataTextField = "District";
        DdlDistrictE.DataValueField = "ID";
        DdlDistrictE.DataBind();
        _cn.Close();

    }

untill now every thing is ok and when I select Item from ddlzoneE ,DdlDistrict's Item change but when I add below code in Page_load Event it didn't worked

  ddlzoneE.Items.FindByText(_dr["zone"].ToString()).Selected = true;
            DdlDistrictE.Items.FindByText(_dr["District"].ToString()).Selected = true;

I mean when I add above code when I select item from ddlzoneE , ddldistrict's Item didn't change

what should I do?

Best Regards

Neda