/// <summary>
        /// PRODUCT QUANTITY TEXT CHANGE
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void ProductQuantitytxt_TextChanged(object sender, EventArgs e)
        {
            int validqnt = 0;

            if (int.TryParse(ProductQuantitytxt.Text, out validqnt))
            {
                CalculateTotalCost(serviceController.CalculateSalCost(ProductQuantitytxt.Text, ProductUnitCosttxt.Text));
                ProductQuantitytxt.Hint = "Product Quantity";
                if (productController.CheckProductQuantitySelected(ProductIDtxt.Text, ProductQuantitytxt.Text))
                {
                    Notificationlbl.Text          = LocalResources.AppConfigResource.QtyWarning;
                    Notificationlbl.ForeColor     = Color.Red;
                    AddSelectedProductbtn.Enabled = false;
                }
                else
                {
                    Notificationlbl.Text          = "";
                    AddSelectedProductbtn.Enabled = true;
                }
            }
            else
            {
                ProductQuantitytxt.Hint = "Invalid Product Quantity";
                TotalCosttxt.Text       = "0";
            }
        }