private void dgvDiscount_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
        {
            if (e.RowIndex == -1)
                return;
            if (dgvDiscount.SelectedRows.Count == Constant.CONSTANT_ZERO)
                return;
            DataGridViewRow selectedRow = dgvDiscount.SelectedRows[Constant.CONSTANT_ZERO];

            string productID = selectedRow.Cells[Constant.OPERATION_INDEX_ONE].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_ONE].Value.ToString();
            string productName = selectedRow.Cells[Constant.OPERATION_INDEX_TWO].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_TWO].Value.ToString();
            string manufacturerName = selectedRow.Cells[Constant.OPERATION_INDEX_THREE].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_THREE].Value.ToString();
            DateTime effectiveDate = (DateTime)selectedRow.Cells[Constant.OPERATION_INDEX_FOUR].Value;
            string bundleUnit = selectedRow.Cells[Constant.OPERATION_INDEX_FIVE].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_FIVE].Value.ToString();
            string freeQuantity = selectedRow.Cells[Constant.OPERATION_INDEX_SIX].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_SIX].Value.ToString();
            string discount = selectedRow.Cells[Constant.OPERATION_INDEX_SEVEN].Value == null ? string.Empty : selectedRow.Cells[Constant.OPERATION_INDEX_SEVEN].Value.ToString();

            AddEditDiscount addEditDiscountForm = new AddEditDiscount(productID, productName, manufacturerName, effectiveDate, bundleUnit, freeQuantity, discount);
            addEditDiscountForm.ShowDialog();
        }
 private void btnAddDiscount_Click(object sender, EventArgs e)
 {
     AddEditDiscount addEditDiscountForm = new AddEditDiscount((DataTable)productBindingSource.DataSource, (DataTable)discountBindingSource.DataSource);
     addEditDiscountForm.ShowDialog();
 }