public void AddProductToCart(TextBox txtQuantity, Label Stock, Label lblErrorSubmit, string userID, string productID)
{
if (Int32.Parse(txtQuantity.Text) > Int32.Parse(Stock.Text) || Int32.Parse(txtQuantity.Text) == 0 || txtQuantity == null)
{
txtQuantity.Text = "";
lblErrorSubmit.Text = "Please input a valid quantity";
lblErrorSubmit.ForeColor = System.Drawing.Color.Red;
lblErrorSubmit.Visible = true;
}
else if (txtQuantity != null)
{
int UserID = Int32.Parse(userID);
int ProductID = Int32.Parse(productID);
int Quantity = Int32.Parse(txtQuantity.Text);
CartHandler.AddToCart(UserID, ProductID, Quantity);
txtQuantity.Text = "";
lblErrorSubmit.ForeColor = System.Drawing.Color.Black;
lblErrorSubmit.Text = "Successfully added to cart.";
lblErrorSubmit.Visible = true;
new ProductHandler().SubstractProductStockById(ProductID, Quantity);
Product NewProduct = new ProductHandler().GetProductByID(ProductID);
Stock.Text = NewProduct.Stock.ToString();
}
}