Shipment/EventListener/AbstractShipmentItemListener.php
public function onUpdate(ResourceEventInterface $event)
    {
        $item = $this->getShipmentItemFromEvent($event);
        $shipment = $item->getShipment();

        $this->preventSaleItemChange($item);

        // Check whether or not the stock impact has been made by the shipment listener
        if (!empty($stateCs = $this->persistenceHelper->getChangeSet($shipment, 'state'))) {
            // If shipment just did a stockable state transition
            if (
                Model\ShipmentStates::hasChangedFromStockable($stateCs) ||
                Model\ShipmentStates::hasChangedToStockable($stateCs)
            ) {
                // Abort (done by the shipment listener)
                return;
            }
        }

        // If shipment is in a stockable state and quantity has changed
        if (
            Model\ShipmentStates::isStockableState($shipment->getState()) &&
            $this->persistenceHelper->isChanged($item, 'quantity')
        ) {
            // Apply shipment item to stock units
            $this->stockUnitAssigner->applyShipmentItem($item);

            $this->scheduleShipmentContentChangeEvent($shipment);
        }
    }
public function onUpdate(ResourceEventInterface $event)
    {
        $item = $this->getShipmentItemFromEvent($event);
        $shipment = $item->getShipment();

        $this->preventSaleItemChange($item);

        // Check whether or not the stock impact has been made by the shipment listener
        if (!empty($stateCs = $this->persistenceHelper->getChangeSet($shipment, 'state'))) {
            // If shipment just did a stockable state transition
            if (
                Model\ShipmentStates::hasChangedFromStockable($stateCs) ||
                Model\ShipmentStates::hasChangedToStockable($stateCs)
            ) {
                // Abort (done by the shipment listener)
                return;
            }
        }

        // If shipment is in a stockable state and quantity has changed
        if (
            Model\ShipmentStates::isStockableState($shipment->getState()) &&
            $this->persistenceHelper->isChanged($item, 'quantity')
        ) {
            // Apply shipment item to stock units
            $this->stockUnitAssigner->applyShipmentItem($item);

            $this->scheduleShipmentContentChangeEvent($shipment);
        }
    }
Update event handler.

@param ResourceEventInterface $event