Custom price of product not getting applied in cart in Magento 2

Question

I am trying to set the custom price of product to cart using Magento2 but unable to do that. For that I have created a module TW - as namespace Cart- as Module name . So under TW/Cart I have created 2 folders etc and Observer. Below is the code in respective folders. Do i need to register this module by putting registration.php file under this module ? Please help me what am I doing wrong?

Code for 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="checkout_cart_product_add_after">
        <observer name="cart_observer_customprice" instance="TW\Cart\Observer\CustomPrice" />
    </event>
</config>

Code for Observer/CustomPrice.php

namespace TW\Cart\Observer;
 use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\App\RequestInterface;
use Psr\Log\LoggerInterface;

class CustomPrice implements ObserverInterface
{
    protected $logger;
    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }
    public function execute(\Magento\Framework\Event\Observer $observer) {


        $item = $observer->getEvent()->getData('quote_item');         
        $item = ( $item->getParentItem() ? $item->getParentItem() : $item );
        $price = 120; //set your price here
        $this->logger->debug("Hello I am here", [
            'price' => $price,
        ]);
        $item->setCustomPrice($price);
        $item->setOriginalCustomPrice($price);
        $item->getProduct()->setIsSuperMode(true);
    }

}

Answer 1

First create a module using free module creator tool called silk software

Magento 2 Module Creator Tool Using Silk Software

and enable using following commands below.

1. php bin/magento module:enable Tw_Cart
2. php bin/magento setup:upgrade
3. php bin/magento setup:di:compile
4. php bin/magento setup:static-content:deploy

create events.xml in the path:- app/code/Tw/Cart/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="checkout_cart_product_add_after">
        <observer name="Tw_Cart_Addtocart_Customprice" instance="TW\Cart\Observer\CustomPrice" />
    </event>
</config>

create CustomPrice.php in the path: app/code/Tw/Cart/Observer/ & keep the below code

<?php
    namespace TW\Cart\Observer;
    use Magento\Framework\Event\ObserverInterface;
    use Magento\Framework\App\RequestInterface;
    use Psr\Log\LoggerInterface;
    class CustomPrice implements ObserverInterface
    {

    public function execute(\Magento\Framework\Event\Observer $observer) 
    {
            $writer = new \Zend\Log\Writer\Stream(BP.'/var/log/stackexchange.log');
            $logger = new \Zend\Log\Logger();
            $logger->addWriter($writer);
            /* Code here */
            $quote_item = $observer->getEvent()->getQuoteItem();
            $price = 400; //set your price here
            $quote_item->setCustomPrice($price);
            $quote_item->setOriginalCustomPrice($price);
            $quote_item->getProduct()->setIsSuperMode(true);
            $logger->info("success !!!!");
    }

}