magento2/app/code/Magento/Sales/Controller/Adminhtml/Invoice/AbstractInvoice/Index.php

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

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

    /**
     * @var \Magento\Framework\View\Result\PageFactory
     */
    protected $resultPageFactory;

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

    /**
     * Init layout, menu and breadcrumb
     *
     * @return \Magento\Backend\Model\View\Result\Page
     */
    protected function _initAction()
    {
        /** @var \Magento\Backend\Model\View\Result\Page $resultPage */
        $resultPage = $this->resultPageFactory->create();
        $resultPage->setActiveMenu('Magento_Sales::sales_invoice')
            ->addBreadcrumb(__('Sales'), __('Sales'))
            ->addBreadcrumb(__('Invoices'), __('Invoices'));
        return $resultPage;
    }

    /**
     * Invoices grid
     *
     * @return \Magento\Backend\Model\View\Result\Page
     */
    public function execute()
    {
        $resultPage = $this->_initAction();
        $resultPage->getConfig()->getTitle()->prepend(__('Invoices'));
        return $resultPage;
    }
}