How check qty before add to cart in magento 2?

Question

I need intercept the product qty before add in cart. I see the events list but don't find any observer to make this action. Any idea? Thanks.

Answer 1

please use below pluging to perform anything before addtocart

app/code/Vendor/Extension/etc/di.xml

<type name="Magento\Checkout\Model\Cart">
        <plugin name="prevent_add_to" type="Vendor\Extension\Plugin\Beforeaddtocart"/>
    </type>

app/code/Vendor/Extension/Plugin/Beforeaddtocart.php

<?php

namespace Vendor\Extension\Plugin;

use Magento\Checkout\Model\Cart;

class Beforeaddtocart
{

    public function beforeAddProduct(Cart $subject, $productInfo, $requestInfo = null)
    {
        // Code that you want to perform before addto cart
        $qty = $requestInfo['qty'];
        return [$productInfo,$requestInfo];
    }
}

Answer 2

You can get the quantity before add to cart using observer event controller_action_predispatch_checkout_cart_add

Please use as below

app/code/Vendor/Module/etc/frontend/events.xml

<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="controller_action_predispatch_checkout_cart_add">
        <observer instance="Vendor\Module\Observer\Frontend\CheckQtyBeforeAddtoCart" name="check_qty_before_add_to_cart"/>
    </event>
</config>

app/code/Vendor/Module/Observer/Frontend/CheckQtyBeforeAddtoCart.php

<?php
/**
 * Copyright ©  All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

namespace Vendor\Module\Observer\Frontend;

class CheckQtyBeforeAddtoCart implements \Magento\Framework\Event\ObserverInterface
{
    protected $_request;
    /**
     * RestrictWebsite constructor.
     */
    public function __construct(
        \Magento\Framework\App\RequestInterface $request
    )
    {
        $this->_request = $request;        
    }

    /**
     * Execute observer
     *
     * @param \Magento\Framework\Event\Observer $observer
     * @return void
     */
    public function execute(
        \Magento\Framework\Event\Observer $observer
    ) {
        $postValues = $this->_request->getPostValue();
        $qty = $postValues['qty'];
    }
}

Hope this will work for you.