Data Controls :: Bind Dropdownlist From Database?

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()

[Code]......

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?