View.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Sales\Controller\Adminhtml\Creditmemo\AbstractCreditmemo;

class View extends \Magento\Backend\App\Action
{
    /**
     * Authorization level of a basic admin session
     *
     * @see _isAllowed()
     */
    const ADMIN_RESOURCE = 'Magento_Sales::sales_creditmemo';

    /**
     * @var \Magento\Backend\Model\View\Result\ForwardFactory
     */
    protected $resultForwardFactory;

    /**
     * @param \Magento\Backend\App\Action\Context $context
     * @param \Magento\Backend\Model\View\Result\ForwardFactory $resultForwardFactory
     */
    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Backend\Model\View\Result\ForwardFactory $resultForwardFactory
    ) {
        $this->resultForwardFactory = $resultForwardFactory;
        parent::__construct($context);
    }

    /**
     * Creditmemo information page
     *
     * @return \Magento\Backend\Model\View\Result\Forward
     */
    public function execute()
    {
        $resultForward = $this->resultForwardFactory->create();
        if ($this->getRequest()->getParam('creditmemo_id')) {
            $resultForward->setController('order_creditmemo');
            $resultForward->setParams(['come_from' => 'sales_creditmemo']);
            $resultForward->forward('view');
        } else {
            $resultForward->forward('noroute');
        }
        return $resultForward;
    }
}