private void frmLapHoaDon_Load(object sender, EventArgs e) { foreach (string ele in nvBUL.LayTenNhanVien()) { cmbTenNhanVien.Items.Add(ele); } if (sphdBUL.LayGioHang() != null) { dgvListSanPhamMua.DataSource = sphdBUL.LayGioHang(); txtThanhTien.Text = Convert.ToString(sphdBUL.ThanhTien()); } }