private void comboBoxSalesNumber_SelectedIndexChanged(object sender, EventArgs e) { if (comboBoxSalesNumber.SelectedIndex != -1 && comboBoxSalesNumber.SelectedIndex != 0) { SalesId = Convert.ToInt32(comboBoxSalesNumber.SelectedValue.ToString()); retrieve.ShowSalesLines(dataGridViewSalesLines, PoLineIdGv, ProductIdGv, ProductNameGv, LineNo, ProductPriceGv, ProductQuantityGv, ProductTotalPrice, UnitGv, Convert.ToInt32(comboBoxSalesNumber.SelectedValue.ToString())); labelGrandTotalValue.Text = (retrieve.GetSalesGrossTotal(Convert.ToInt32(comboBoxSalesNumber.SelectedValue.ToString()))).ToString(); } }