public void them_YeuCau(string maMH, string ten, string sl)
        {
            string stt = (ListMHDN.Count + 1).ToString();

            ListMatHangKho mh_kho = new ListMatHangKho(stt, maMH, ten, sl);

            ListMHDN.Add(mh_kho);
        }
        public void search()
        {
            ListMatHang.Clear();

            ObservableCollection <MATHANG> list_mh = new ObservableCollection <MATHANG>(DataProvider.Ins.DB.MATHANGs);

            int stt = 1;

            foreach (var mh in list_mh)
            {
                if (duyet_MatHang(mh, txtMaMH, txtTenMH))
                {
                    ListMatHangKho mh_kho = new ListMatHangKho(stt + "", mh.MaMH, mh.TenMH, get_TonKho(mh.MaMH));
                    ListMatHang.Add(mh_kho);
                    stt++;
                }
            }
        }