getAdminBlock example

// Only render accessible links.       if (!$element->access->isAllowed()) {
        continue;
      }

      $link = $element->link;
      $block['title'] = $link->getTitle();
      $block['description'] = $link->getDescription();
      $block['content'] = [
        '#theme' => 'admin_block_content',
        '#content' => $this->systemManager->getAdminBlock($link),
      ];

      if (!empty($block['content']['#content'])) {
        $blocks[$key] = $block;
      }
    }

    if ($blocks) {
      ksort($blocks);
      $build = [
        '#theme' => 'admin_page',
        

  public function getBlockContents() {
    // We hard-code the menu name here since otherwise a link in the tools menu     // or elsewhere could give us a blank block.     $link = $this->menuActiveTrail->getActiveLink('admin');
    if ($link && $content = $this->getAdminBlock($link)) {
      $output = [
        '#theme' => 'admin_block_content',
        '#content' => $content,
      ];
    }
    else {
      $output = [
        '#markup' => t('You do not have any administrative items.'),
      ];
    }
    return $output;
  }