protected void GetUsersBillsForSite(object sender, DirectEventArgs e)
        {
            if (BillDateField.SelectedValue != null && FilterUsersBySite.SelectedItem != null)
            {
                int siteId = Convert.ToInt32(FilterUsersBySite.SelectedItem.Value);

                DateTime beginningOfTheMonth = new DateTime(BillDateField.SelectedDate.Year, BillDateField.SelectedDate.Month, 1);
                DateTime endOfTheMonth       = beginningOfTheMonth.AddMonths(1).AddDays(-1);

                UsersBillsGrid.GetStore().DataSource = GetUsersBills(siteId, beginningOfTheMonth, endOfTheMonth);
                UsersBillsGrid.GetStore().DataBind();
            }
        }
        protected void FilterUsersBySite_Selected(object sender, DirectEventArgs e)
        {
            if (FilterUsersBySite.SelectedItem.Index != -1 && !string.IsNullOrEmpty(FilterUsersBySite.SelectedItem.Value))
            {
                BillDateField.Disabled = false;
                if (BillDateField.SelectedValue != null)
                {
                    int siteId = Convert.ToInt32(FilterUsersBySite.SelectedItem.Value);

                    DateTime beginningOfTheMonth = new DateTime(BillDateField.SelectedDate.Year, BillDateField.SelectedDate.Month, 1);
                    DateTime endOfTheMonth       = beginningOfTheMonth.AddMonths(1).AddDays(-1);

                    UsersBillsGrid.GetStore().DataSource = GetUsersBills(siteId, beginningOfTheMonth, endOfTheMonth);
                    UsersBillsGrid.GetStore().DataBind();
                }
            }
            else
            {
                BillDateField.Disabled = true;
                //BillDateField.Clear();
                //UsersBillsGrid.ClearContent();
            }
        }