How to populate dropdown in a modal popup panel from code behind

protected void btnFill_Click(object sender, EventArgs e)
{
   foreach (GridViewRow rw in gvGrid.Rows)
   {
                    CheckBox chkBx = (CheckBox)rw.FindControl("chkSelect");
                    if (chkBx != null && chkBx.Checked)
                    {
                            HyperLink hpr = (HyperLink)rw.FindControl("hpr");
                            arlMyarylst.Add(hpr.Text.Trim());
                    }
   }
ddlID.Datasource = arlMyarylst;
ddlID.dataBind();
mpeMyModal.Show();
}