void btnThemMoi_Click(object sender, EventArgs e)
{
en.TenSP = txtTenSP.Text;
en.DonVi = txtDonVi.Text;
en.DonGia = float.Parse(txtDonGia.Text);
en.SoTon = Int64.Parse(txtSoTon.Text);
en.MaLoai = cboLoaiSP.SelectedValue.ToString();
bus.insertdata(en);
MessageBox.Show("Đã thêm 1 dòng");
NapSanPham();
XoaForm();
}