Kdjykuj

I tried my code below to get Qty from observer when a page loaded :

Observer :

public function execute(MagentoFrameworkEventObserver $observer) {

    $collections = $observer->getEvent()->getCollection();

    foreach( $collections as $collection ) {

        var_dump($collection->getQty());

    }

}

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="catalog_product_collection_load_after">

    <observer name="loadupdates" instance="TestShowObserverCustomPrice" />

  </event>

</config>

But, i got all NULL for getQty of products. So my question, how can i get the Qty of products, and how to update the Qty from the observer?

If you want to get Inventory of the product, you should inject MagentoCatalogInventoryApiStockStateInterface first. Then using getStockQty to get the qty of an product. So that in your observer:

public function __construct(

    MagentoCatalogInventoryApiStockStateInterface $stockItem

)

{

    $this->stockItem = $stockItem;

}



public function execute(MagentoFrameworkEventObserver $observer) {

    $collections = $observer->getEvent()->getCollection();

    foreach( $collections as $collection ) {

        var_dump($this->stockItem->getStockQty($collection->getId()));

    }

}

Ref: How to get stock quantity of each product in Magento 2

If you want to $productobj after saving product from backend side so you can easily use catalog_product_save_after event.

I am assuming that you already know how to create a module in M2.

Right now you have to need develop new module for M2

Then Create this events.xml file in below path

appcodeYOUR_NAMESPACEYOURMODULEetcadminhtml

<?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="catalog_product_save_after">

        <observer name="test_name" instance="YOUR_NAMESPACEYOUR_MODULENAMEObserverProductsaveafter" />

    </event>

</config>

And Create your observer file Productsaveafter.php in below path

appcodeYOUR_NAMESPACEYOURMODULEObserver

<?php



namespace YOURNAMESPACEYOURMODULENAMEObserver;



use MagentoFrameworkEventObserverInterface;



class Productsaveafter implements ObserverInterface

{    

    public function execute(MagentoFrameworkEventObserver $observer)

    {

        $product = $observer->getEvent()->getProduct();

        $id = $product->getId(); //Get Product Id



        //Get Quantity

        $stockItem = $product->getExtensionAttributes()->getStockItem();

        $stockData = $stockItem->getQty();

        // Get new Qty

        $_vendor_qty = $product->getVendorQty();

        $_on_hand_qty = $product->getOnHandQty();

        $totalQty = $_vendor_qty+$_on_hand_qty; //Add New Qty





        $stockItem->setQty($totalQty); //Set New Qty to Main Qty

        $stockItem->save();



    }   

}