private void txtSoLuong_TextChanged(object sender, EventArgs e)
{
if (txtSoLuong.Text != string.Empty)
{
if (int.Parse(txtSoLuong.Text) > 0 && int.Parse(txtSoLuong.Text) < hd_bll.GetSoLuong(cboMaSP.SelectedValue.ToString()))
{
decimal thanhtien = decimal.Parse(txtDonGia.Text.ToString()) * int.Parse(txtSoLuong.Text);
txtTongTien.Text = Convert.ToString(thanhtien);
}
else
{
txtTongTien.Text = "0";
}
}
}