private void cmsMenu_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
        {
            bool   night = false;
            int    section;
            string sn  = e.ClickedItem.Text;
            int    dow = currentCellColumnIndex;

            if (currentCellRowIndex < Global.LessonPerMorning)
            {
                morning = true;
                night   = false;
                section = currentCellRowIndex;
            }
            else if (currentCellRowIndex < Global.LessonPerDay + Global.LessonPerMorning)
            {
                morning = false;
                night   = false;
                section = currentCellRowIndex - Global.LessonPerMorning;
            }
            else
            {
                night   = true;
                morning = false;
                section = currentCellRowIndex - Global.LessonPerDay - Global.LessonPerMorning;
            }
            int ti = (int)e.ClickedItem.Tag;

            if (morning)
            {
                StaticSQLiteHelper.ReforceSetMorningLesson(currentClassID, dow, section, ti);
            }
            else if (night)
            {
                StaticSQLiteHelper.ReforceSetNightLesson(currentClassID, dow, section, ti);
            }
            else
            {
                StaticSQLiteHelper.ReforceSetLesson(currentClassID, dow, section, ti);
            }

            if (ti == 0)
            {
                dgv.Rows[currentCellRowIndex].Cells[currentCellColumnIndex].Value = "";
            }
            else
            {
                dgv.Rows[currentCellRowIndex].Cells[currentCellColumnIndex].Value = sn.Substring(0, 1);
            }

            loadHistory();
        }