How to add metatags in hook_preproccess_node()?

Question

How to add variable meta tags depending on the node that is loaded?

The node has a picture and custom title field and the need to be variable. What is the best practice to change them in: hook_preprocess_node()?

Answer 1

I am aware that this does not directly answer the question, which was about adding in a preprocess function, but I would suggest that you also consider the metatag module, which is pretty full featured.

https://www.drupal.org/project/metatag

Answer 2

yes, you can, place this code in template.php in your subtheme folder

function yourtheme_preprocess_node(&$vars) {
        $element = array(
          '#tag' => 'meta', 
          '#attributes' => array(
            'name' => 'robots', 
            'content' => 'index',
          ),
        );
        drupal_add_html_head($element, 'robots');
 } 

Answer 3

For me the following worked: I managed to load the current node in the hook_preprocess_node(). Based on this answer: How do I get the current node ID?

function module_name_page_attachments_alter(array &$page) {

            $node = \Drupal::routeMatch()->getParameter('node');
            if ($node instanceof \Drupal\node\NodeInterface) {
            // You can get nid and anything else you need from the node object.
            $nid = $node->id();
        }

        $ogImage = array(
            '#tag' => 'meta',
            '#attributes' => array(
                'property' => 'og:image',
                'content' => 'location of the image'.$nid.'.png',
    //my picture has the node id before the file format
            ),
        );

        $page['#attached']['html_head'][] = [$ogImage, 'ogImage'];
    }