private void btnLuu_Click(object sender, EventArgs e)
{
int sl = int.Parse(txtSL.Text);
long gia = long.Parse(txtGiaNhap.Text);
long thanhtien = (long)sl * gia;
long masp = long.Parse(cbbMaSP.SelectedValue.ToString());
CTPNDTO ctpn = new CTPNDTO(maphieu, masp, sl, gia, thanhtien);
PhieuNhapBUS.InsertCTPN(ctpn);
dgvNhapHang.DataSource = PhieuNhapBUS.GetCTPN(maphieu);
}