I implement a menu on a region using a preprocess function to get a link with an anchor for each block of it with a title. I made a preprocess function for region, in my theme, where I test the region machine name.

I first used the $variables[‘elements’][XXX][‘#id’] to load each block, to find out if the label was set to be display. But I quickly discover that on my server, where the cache is on, the $variables[‘elements’] only contain an array of cached render.

I then modify my preprocess hook to use the key of the $variables[‘elements’], witch is finally the block key.

use DrupalblockEntityBlock;  /**  * Implements hook_preprocess_region().  */ function MYTHEME_preprocess_region(&$variables) {   if ($variables['region'] == 'one_page') {     $blocs_menu = array();     foreach ($variables['elements'] as $key => $values) {       if (substr($key, 0, 1) == '#') {         continue;       }       $bloc_object = Block::load($key);       if (is_object($bloc_object)) {         $bloc_settings = $bloc_object->get('settings');         if ($bloc_settings['label_display']) {           $blocs_menu[] = array(               'id' => $key,               'label' => $bloc_settings['label'],           );         }       }     }     if (count($blocs_menu)) {       $variables['region_menu'] = $blocs_menu;     }   } } 

And in my override file region–one-page.html.twig

{%- if region_menu -%} <nav class="page-nav-anchor">   <ul> {%- for menu in region_menu -%}   <li><a rel="scroll" href="#block-{{ menu['id'] }}">{{ menu['label'] }}</a></li> {%- endfor -%}   </ul> </nav> {%- endif -%} 

Everything is working well, but I would like to improve the concept :

• Be able to detect if the cache is activated on the project
• Include in cache my ‘region_menu’ variable, and generate it only when cache have to be rebuild.

If I understand well, the twig template is also cached, then it is maybe just not really necessary to declare the menu if cache is ON ?

The thing is I’m really lost in the D8 cache API. I think I have to deal with the cache tags, because I don’t have a render to cache.

I would appreciate some help, I cannot find some good (and easy) examples on the documentation or in the core modules.