protected void BindDataToGridView()
{
//get data from database
DataTable dt = AdminDb.GetAllCities(tbFindCity.Text, ddMajorFilter.SelectedValue);
//cast to dataview for sorting and filtering
DataView dv = (DataView)dt.DefaultView;
//sort by session expr and direction
dv.Sort = Session["SortExpr"].ToString() + Session["SortDirection"].ToString();
//rebind with new sorted data
gvCities.DataSource = dv;
gvCities.DataBind();
}