Magento 2 – Adding a Non-Category Link to Navigation Links

category-navigationmagento2

I'm not sure what I'm doing wrong here. The block which holds the category links in is referenced to as navigation.sections. I thought by directing the following arguments toward the container I would be able to create a new link under it. Any help is appreciated.

<referenceContainer name="navigation.sections">
            <block class="Magento\Framework\View\Element\Html\Links" name="mylink">
                    <arguments>
                        <argument name="label" xsi:type="string">Mylink</argument>
                        <argument name="path" xsi:type="string">mypath</argument>
                        <argument name="css_class" xsi:type="string">mycss</argument>
                    </arguments>
            </block>
</referenceContainer>

Best Answer

[EDIT]
Apparently, in latest versions of M2 this does not work anymore.
Thanks to Max for pointing this out.
For later version you need to add a plugin for Magento\Theme\Block\Html\Topmenu instead of an observer.
Add this to etc/frontend/di.xml 

<type name="Magento\Theme\Block\Html\Topmenu">
    <plugin name="[module]-topmenu" type="[Namespace]\[Module]\Plugin\Block\Topmenu" />
</type>

and create the plugin class file [Namespace]/[Module]/Plugin/Block/Topmenu.php 

<?php 

namespace [Namespace]\[Module]\Plugin\Block;

use Magento\Framework\Data\Tree\NodeFactory;

class Topmenu
{
    /**
     * @var NodeFactory
     */
    protected $nodeFactory;

    public function __construct(
        NodeFactory $nodeFactory
    ) {
        $this->nodeFactory = $nodeFactory;
    }

    public function beforeGetHtml(
        \Magento\Theme\Block\Html\Topmenu $subject,
        $outermostClass = '',
        $childrenWrapClass = '',
        $limit = 0
    ) {
        $node = $this->nodeFactory->create(
            [
                'data' => $this->getNodeAsArray(),
                'idField' => 'id',
                'tree' => $subject->getMenu()->getTree()
            ]
        );
        $subject->getMenu()->addChild($node);
    }

    protected function getNodeAsArray()
    {
        return [
            'name' => __('Label goes here'),
            'id' => 'some-unique-id-here',
            'url' => 'http://www.example.com/',
            'has_active' => false,
            'is_active' => false // (expression to determine if menu item is selected or not)
        ];
    }
}

[/EDIT]
Original answer:
You can add elements to the top menu using the event page_block_html_topmenu_gethtml_before.

So you need to create a module with these files (all the files should be in app/code/[Namespace]/[Module]):

etc/module.xml - the module declaration file

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="[Namespace]_[Module]" setup_version="2.0.0">
        <sequence>
            <module name="Magento_Theme"/>
        </sequence>
    </module>
</config>

registration.php - the registration file

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    '[Namespace]_[Module]',
    __DIR__
);

etc/frontend/events.xml - the events declaration file

<?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="page_block_html_topmenu_gethtml_before">
        <observer name="[namespace]_[module]_observer" instance="[Namespace]\[Module]\Observer\Topmenu" />
    </event>
</config>

Observer/Topmenu.php - the actual observer

<?php
namespace [Namespace]\[Module]\Observer;
use Magento\Framework\Event\Observer as EventObserver;
use Magento\Framework\Data\Tree\Node;
use Magento\Framework\Event\ObserverInterface;
class Topmenu implements ObserverInterface
{
    public function __construct(
        ...//add dependencies here if needed
    )
    {
    ...
    }
    /**
     * @param EventObserver $observer
     * @return $this
     */
    public function execute(EventObserver $observer)
    {
        /** @var \Magento\Framework\Data\Tree\Node $menu */
        $menu = $observer->getMenu();
        $tree = $menu->getTree();
        $data = [
            'name'      => __('Menu item label here'),
            'id'        => 'some-unique-id-here',
            'url'       => 'url goes here',
            'is_active' => (expression to determine if menu item is selected or not)
        ];
        $node = new Node($data, 'id', $tree, $menu);
        $menu->addChild($node);
        return $this;
    }
}

Now run in the cli php bin/magento setup:upgrade to install the module and you are good to go.

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