Setting a custom item subtotal when adding product to cart?

Question

Magento 2.4

I already have my observer in place, but setting a custom subtotal for my item does not work. I am listening to the checkout_cart_product_add_after event. This is my observer code:

$item = $observer->getEvent()->getData('quote_item');
$item->setQty(3); // works
$item->setCustomPrice(250); // works
$item->setOriginalCustomPrice(250); // works
$item->getQuote()->setSubtotal(250); // does NOT work ?
$item->setSubtotal(250); // does NOT work either?

No matter, it always multiplies the 250 (custom price) by 3 (custom qty). Any ideas how to solve this?

Answer 1

Check to see if $item->getQuote()->getId() gives a valid quote ID. If it does not then you may not have access to the quote itself and can try adding:

use \Magento\Checkout\Model\Cart;

...

/**
* @var \Magento\Checkout\Model\Cart
*/
protected $cart;

...

public function __construct(
        ...
        Cart $cart
        ...
    ) {

...

$quote = $cart->getQuote();

You should then have access to the quote itself. Note: This was done from memory so shout if you have any issues and I will take a closer look.