private void btnSua_Click(object sender, EventArgs e)
        {
            frmHangHoa_ADD fm = new frmHangHoa_ADD(mahang, tenhang, tennhacungcap, tennhomhang, donvitinh, giaban, ngaycapnhat);

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

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