private void btnTraCuuTheoLop_ItemClick(object sender, ItemClickEventArgs e)
        {
            TraCuuTheoLopForm frm = new TraCuuTheoLopForm(this, Ngay);

            frm.MdiParent = this;
            frm.Show();
        }
        private void dateNgay_EditValueChanged(object sender, EventArgs e)
        {
            Ngay = (DateTime)dateNgay.EditValue;
            if (HocKy == null)
            {
                return;
            }
            int check = Ngay.CompareTo(HocKy.ngayBatDau);

            if (Ngay.CompareTo(HocKy.ngayBatDau) <= 0 || Ngay.CompareTo(HocKy.ngayKetThuc) >= 0)
            {
                Ngay = DateTime.Now;
                dateNgay.EditValue = Ngay;
                return;
            }
            if (this.ActiveMdiChild == null)
            {
                return;
            }

            string fname = this.ActiveMdiChild.Name;

            if (fname == "TraCuuTheoLopForm")
            {
                TraCuuTheoLopForm frm = (TraCuuTheoLopForm)this.ActiveMdiChild;
                frm.SetDate(Ngay);
            }
            foreach (Form frm in this.MdiChildren)
            {
                if (frm.Name == "TraCuuTheoLopForm")
                {
                    TraCuuTheoLopForm f = (TraCuuTheoLopForm)frm;
                    f.SetDate(Ngay);
                }
                else if (frm.Name == "XepTietHocForm")
                {
                    XepTietHocForm f = (XepTietHocForm)frm;
                    f.SetDate(Ngay);
                }
            }
        }