private void themsp_Click(object sender, EventArgs e)
{
if (txbMaHoaDon.Text != "")
{
ChiTietHoaDon chiTietHoaDon = new ChiTietHoaDon();
chiTietHoaDon.mhd = txbMaHoaDon.Text;
chiTietHoaDon.ShowDialog();
tongtien.Text = dao.getPrice(txbMaHoaDon.Text);
}
}