private void Them_button_Click(object sender, EventArgs e)
        {
            HoiDongThem f = new HoiDongThem();

            f.Show();
            f.d += new HoiDongThem.ThemNguoiDelegate(AddHD);
        }
        private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            var senderGrid = (DataGridView)sender;

            if (senderGrid.Columns[e.ColumnIndex] is DataGridViewButtonColumn &&
                e.RowIndex >= 0 && senderGrid.Columns[e.ColumnIndex].Name == "ChiTiet")
            {
                HOI_DONG HD = _hds[e.RowIndex];
                _curIndex = e.RowIndex;
                HoiDongThem f = new HoiDongThem(HD);
                f.d += new HoiDongThem.ThemNguoiDelegate(EditHD);
                f.Show();
            }
            else if (senderGrid.Columns[e.ColumnIndex] is DataGridViewButtonColumn &&
                     e.RowIndex >= 0 && senderGrid.Columns[e.ColumnIndex].Name == "Xoa")
            {
                _hds.RemoveAt(e.RowIndex);
                LoadHD();
            }
        }