private void btnBill_Mng_Click(object sender, EventArgs e)
        {
            UCQLHoaDon ucBill = new UCQLHoaDon();

            if (getFlagUserControl(FLAG_BILL) == USER_ON)
            {
                frmChinh.Activate();
                return;
            }
            FLAG_BILL = USER_ON;
            LoadUser(ucBill);
        }
        private void pictureBox2_Click(object sender, EventArgs e)
        {
            UCQLHoaDon uccthd = new UCQLHoaDon();

            LoadUser(uccthd);
        }