private void cmbClass_EditValueChanged(object sender, EventArgs e) { var dc = new ClassSRMDataContext(Config.connection); string date = txtDate.Text.Substring(0, 7); int count = (cmbClass.Properties.DataSource as IList).Count; if (count > 0) { gridControl1.DataSource = dc.SelectTopMonth((int)cmbClass.EditValue, date + "/01", date + "/31"); } }