Magento 2 Overwrites Topmenu.php In Module But Menu Nav Disappears

Question

My di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Theme\Block\Html\Topmenu" type="Vendor\TopMenu\Plugin\Block\Topmenu" />
</config>

My Topmenu.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Vendor\TopMenu\Plugin\Block\Html;

use Magento\Framework\Data\Tree\Node;
use Magento\Framework\Data\Tree\NodeFactory;
use Magento\Framework\Data\TreeFactory;
use Magento\Framework\DataObject\IdentityInterface;
use Magento\Framework\View\Element\Template;

/**
 * Html page top menu block
 *
 * @api
 * @since 100.0.2
 */
class Topmenu extends Template implements IdentityInterface
{
    /**
     * Cache identities
     *
     * @var array
     */
    protected $identities = [];

    /**
     * Top menu data tree
     *
     * @var \Magento\Framework\Data\Tree\Node
     */
    protected $_menu;

    /**
     * @var NodeFactory
     */
    private $nodeFactory;

    /**
     * @var TreeFactory
     */
    private $treeFactory;

    /**
     * @param Template\Context $context
     * @param NodeFactory $nodeFactory
     * @param TreeFactory $treeFactory
     * @param array $data
     */
    public function __construct(
        Template\Context $context,
        NodeFactory $nodeFactory,
        TreeFactory $treeFactory,
        array $data = []
    ) {
        parent::__construct($context, $data);
        $this->nodeFactory = $nodeFactory;
        $this->treeFactory = $treeFactory;
    }

    /**
     * Get block cache life time
     *
     * @return int
     * @since 100.1.0
     */
    protected function getCacheLifetime()
    {
        return parent::getCacheLifetime() ?: 3600;
    }

    /**
     * Get top menu html
     *
     * @param string $outermostClass
     * @param string $childrenWrapClass
     * @param int $limit
     * @return string
     */
    public function getHtml($outermostClass = '', $childrenWrapClass = '', $limit = 0)
    {
        $this->_eventManager->dispatch(
            'page_block_html_topmenu_gethtml_before',
            ['menu' => $this->getMenu(), 'block' => $this, 'request' => $this->getRequest()]
        );

        $this->getMenu()->setOutermostClass($outermostClass);
        $this->getMenu()->setChildrenWrapClass($childrenWrapClass);

        $html = $this->_getHtml($this->getMenu(), $childrenWrapClass, $limit);

        $transportObject = new \Magento\Framework\DataObject(['html' => $html]);
        $this->_eventManager->dispatch(
            'page_block_html_topmenu_gethtml_after',
            ['menu' => $this->getMenu(), 'transportObject' => $transportObject]
        );
        $html = $transportObject->getHtml();
        return $html;
    }

    /**
     * Count All Subnavigation Items
     *
     * @param \Magento\Backend\Model\Menu $items
     * @return int
     */
    protected function _countItems($items)
    {
        $total = $items->count();
        foreach ($items as $item) {
            /** @var $item \Magento\Backend\Model\Menu\Item */
            if ($item->hasChildren()) {
                $total += $this->_countItems($item->getChildren());
            }
        }
        return $total;
    }

    /**
     * Building Array with Column Brake Stops
     *
     * @param \Magento\Backend\Model\Menu $items
     * @param int $limit
     * @return array|void
     *
     * @todo: Add Depth Level limit, and better logic for columns
     */
    protected function _columnBrake($items, $limit)
    {
        $total = $this->_countItems($items);
        if ($total <= $limit) {
            return;
        }

        $result[] = ['total' => $total, 'max' => (int)ceil($total / ceil($total / $limit))];

        $count = 0;
        $firstCol = true;

        foreach ($items as $item) {
            $place = $this->_countItems($item->getChildren()) + 1;
            $count += $place;

            if ($place >= $limit) {
                $colbrake = !$firstCol;
                $count = 0;
            } elseif ($count >= $limit) {
                $colbrake = !$firstCol;
                $count = $place;
            } else {
                $colbrake = false;
            }

            $result[] = ['place' => $place, 'colbrake' => $colbrake];

            $firstCol = false;
        }

        return $result;
    }

    /**
     * Add sub menu HTML code for current menu item
     *
     * @param \Magento\Framework\Data\Tree\Node $child
     * @param string $childLevel
     * @param string $childrenWrapClass
     * @param int $limit
     * @return string HTML code
     */
    protected function _addSubMenu($child, $childLevel, $childrenWrapClass, $limit)
    {
        $html = '';
        if (!$child->hasChildren()) {
            return $html;
        }

        $colStops = null;
        if ($childLevel == 0 && $limit) {
            $colStops = $this->_columnBrake($child->getChildren(), $limit);
        }

        $html .= '<ul class="level' . $childLevel . ' ' . $childrenWrapClass . '">';
        $html .= $this->_getHtml($child, $childrenWrapClass, $limit, $colStops);
        $html .= '</ul>';

        return $html;
    }

    /**
     * Recursively generates top menu html from data that is specified in $menuTree
     *
     * @param \Magento\Framework\Data\Tree\Node $menuTree
     * @param string $childrenWrapClass
     * @param int $limit
     * @param array $colBrakes
     * @return string
     *
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     * @SuppressWarnings(PHPMD.NPathComplexity)
     */
    protected function _getHtml(
        \Magento\Framework\Data\Tree\Node $menuTree,
        $childrenWrapClass,
        $limit,
        $colBrakes = []
    ) {
        $html = '';

        $children = $menuTree->getChildren();
        $parentLevel = $menuTree->getLevel();
        $childLevel = $parentLevel === null ? 0 : $parentLevel + 1;

        $counter = 1;
        $itemPosition = 1;
        $childrenCount = $children->count();

        $parentPositionClass = $menuTree->getPositionClass();
        $itemPositionClassPrefix = $parentPositionClass ? $parentPositionClass . '-' : 'nav-';

        /** @var \Magento\Framework\Data\Tree\Node $child */
        foreach ($children as $child) {
            if ($childLevel === 0 && $child->getData('is_parent_active') === false) {
                continue;
            }
            $child->setLevel($childLevel);
            $child->setIsFirst($counter == 1);
            $child->setIsLast($counter == $childrenCount);
            $child->setPositionClass($itemPositionClassPrefix . $counter);

            $outermostClassCode = '';
            $outermostClass = $menuTree->getOutermostClass();

            if ($childLevel == 0 && $outermostClass) {
                $outermostClassCode = ' class="' . $outermostClass . '" ';
                $child->setClass($outermostClass);
            }

            if (count($colBrakes) && $colBrakes[$counter]['colbrake']) {
                $html .= '</ul></li><li class="column"><ul>';
            }

            $html .= '<li ' . $this->_getRenderedMenuItemAttributes($child) . '>';
            $html .= '<a href="' . $child->getUrl() . '" ' . $outermostClassCode . '><span>' . $this->escapeHtml(
                $child->getName()
            ) . '</span></a>' . $this->_addSubMenu(
                $child,
                $childLevel,
                $childrenWrapClass,
                $limit
            ) . '</li>';
            $itemPosition++;
            $counter++;
        }

        if (count($colBrakes) && $limit) {
            $html = '<li class="column"><ul>' . $html . '</ul></li>';
        }

        return $html;
    }

    /**
     * Generates string with all attributes that should be present in menu item element
     *
     * @param \Magento\Framework\Data\Tree\Node $item
     * @return string
     */
    protected function _getRenderedMenuItemAttributes(\Magento\Framework\Data\Tree\Node $item)
    {
        $html = '';
        $attributes = $this->_getMenuItemAttributes($item);
        foreach ($attributes as $attributeName => $attributeValue) {
            $html .= ' ' . $attributeName . '="' . str_replace('"', '\"', $attributeValue) . '"';
        }
        return $html;
    }

    /**
     * Returns array of menu item's attributes
     *
     * @param \Magento\Framework\Data\Tree\Node $item
     * @return array
     */
    protected function _getMenuItemAttributes(\Magento\Framework\Data\Tree\Node $item)
    {
        $menuItemClasses = $this->_getMenuItemClasses($item);
        return ['class' => implode(' ', $menuItemClasses)];
    }

    /**
     * Returns array of menu item's classes
     *
     * @param \Magento\Framework\Data\Tree\Node $item
     * @return array
     */
    protected function _getMenuItemClasses(\Magento\Framework\Data\Tree\Node $item)
    {
        $classes = [];

        $classes[] = 'level' . $item->getLevel();
        $classes[] = $item->getPositionClass();

        if ($item->getIsFirst()) {
            $classes[] = 'first';
        }

        if ($item->getIsActive()) {
            $classes[] = 'active';
        } elseif ($item->getHasActive()) {
            $classes[] = 'has-active';
        }

        if ($item->getIsLast()) {
            $classes[] = 'last';
        }

        if ($item->getClass()) {
            $classes[] = $item->getClass();
        }

        if ($item->hasChildren()) {
            $classes[] = 'parent';
        }

        return $classes;
    }

    /**
     * Add identity
     *
     * @param array $identity
     * @return void
     */
    public function addIdentity($identity)
    {
        if (!in_array($identity, $this->identities)) {
            $this->identities[] = $identity;
        }
    }

    /**
     * Get identities
     *
     * @return array
     */
    public function getIdentities()
    {
        return $this->identities;
    }

    /**
     * Get cache key informative items
     *
     * @return array
     * @since 100.1.0
     */
    public function getCacheKeyInfo()
    {
        $keyInfo = parent::getCacheKeyInfo();
        $keyInfo[] = $this->getUrl('*/*/*', ['_current' => true, '_query' => '']);
        return $keyInfo;
    }

    /**
     * Get tags array for saving cache
     *
     * @return array
     * @since 100.1.0
     */
    protected function getCacheTags()
    {
        return array_merge(parent::getCacheTags(), $this->getIdentities());
    }

    /**
     * Get menu object.
     *
     * Creates \Magento\Framework\Data\Tree\Node root node object.
     * The creation logic was moved from class constructor into separate method.
     *
     * @return Node
     * @since 100.1.0
     */
    public function getMenu()
    {
        if (!$this->_menu) {
            $this->_menu = $this->nodeFactory->create(
                [
                    'data' => [],
                    'idField' => 'root',
                    'tree' => $this->treeFactory->create()
                ]
            );
        }
        return $this->_menu;
    }
}

This works! But the Menu just gone ? Anyone have any idea?

Answer 1

The categories are added to the menu using a plugin Magento\Catalog\Plugin\Block\Topmenu::beforeGetHtml.
Since you replaced the core block with yours, this plugin does not get executed.

Make your class extend Magento\Theme\Block\Html\Topmenu. Plugins will be called for child classes also, hence it will be called for yours.