private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
        {
            // Process for UI control ""
            if (dataGridView1.CurrentRow != null)
            {
                int index = dataGridView1.CurrentRow.Index;
                //Console.WriteLine("Size: " + index);
                DataGridViewRow dgvRow = dataGridView1.CurrentRow;

                if (dgvRow.Cells["dgvtxtSoLuong"].Value != null && dgvRow.Cells["dgvcbcSach"].Value != null)
                {
                    //Console.WriteLine("Value: " + Convert.ToString(dgvRow.Cells["dgvcbcSach"].Value));
                    dataGridView1.Rows[index].Cells["dgvtxtThanhTien"].Value =
                        Convert.ToInt32(dgvRow.Cells["dgvtxtSoLuong"].Value) * bus_Sach.getGiaSach(Convert.ToString(dgvRow.Cells["dgvcbcSach"].Value));
                }
                SumMoney();
            }
        }