private void btnSua_Click(object sender, EventArgs e)
        {
            frmTonDauKy fm = new frmTonDauKy(mamathang, ngaycapnhat, soluong, giatriton);

            fm.FormClosed += Fm_FormClosed;
            fm.ShowDialog();
        }
        private void btnThem_Click(object sender, EventArgs e)
        {
            frmTonDauKy fm = new frmTonDauKy();

            fm.FormClosed += Fm_FormClosed;
            fm.ShowDialog();
        }