Common D8 Preprocess Functions

common_preprocesses.theme

<?php

/**
 * @file
 * Example of some commonly used functions.
 */

use Drupal\Core\Link;
use Drupal\Core\Url;
use Drupal\Component\Utility\Html;
use Drupal\node\Entity\Node;

/**
 * Implements hook_preprocess_html().
 */
function hook_preprocess_html(&$variables) {
  // If is homepage.
  $variables['attributes']['class'][] = \Drupal::service('path.matcher')
    ->isFrontPage() ? 'frontpage' : '';
  // Node type class.
  $variables['attributes']['class'][] = isset($variables['node_type']) ? 'page-node-type--' . $variables['node_type'] : '';
  // Logged in class.
  $variables['attributes']['class'][] = $variables['logged_in'] ? 'logged-in' : 'logged-out';
}

/**
 * Implements hook_preprocess_node().
 */
function hook_preprocess_node(&$variables) {
  $node = $variables['node'];
  $type = $node->getType();
  $mode = $variables['view_mode'];
  $variables['attributes']['class'][] = 'node-type-' . $type;
  $variables['attributes']['class'][] = 'node-mode-' . $mode;
  $variables['attributes']['class'][] = 'node-type-' . $type . '-mode-' . $mode;

  // Example of how to build a link the "Drupal" way
  // You probabbly get the value in the quotes from a field
  // It might need another URL::fromXYZ function, depending on input
  // See https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Url.php/class/Url/8.6.x
  $my_url = URL::fromUri('https://www.some-url.com/');
  // Set the text or markup you want inside the link
  $my_text = t('Click Me!');
  // Set any attributes you want as an array
  $link_options = [
    'attributes' => [
      'target' => '_blank',
      'class' => ['btn', 'btn--large'],
    ],
  ];
  $my_url->setOptions($link_options);
  // See https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Link.php/function/Link%3A%3AfromTextAndUrl/8.5.x
  $my_full_link = Link::fromTextAndUrl($my_text, $my_url)->toString();
}

/**
 * Implements hook_preprocess_media().
 */
function hook_preprocess_media(&$variables) {
  $mediaType = $variables['media']->bundle();
  $variables['attributes']['class'][] = 'media-entity';
  $variables['attributes']['class'][] = 'media-type-' . $mediaType;
}

/**
 * Implements hook_preprocess_menu().
 */
function hook_preprocess_menu(&$variables) {
  if (!isset($variables['attributes']['class'])) {
    $variables['attributes']['class'] = [];
  }

  if (!isset($variables['menu_name'])) {
    return;
  }

  $variables['attributes']['class'][] = 'menu--' . $variables['menu_name'];
}

/**
 * Implements hook_preprocess_field().
 */
function hook_preprocess_field(&$variables) {
  $field_name = $variables['field_name'];

  // Add a class specifying what field we're looking at.
  if (!isset($variables['attributes']['class'])) {
    $variables['attributes']['class'] = [];
  }
  $name_class = 'field-name--' . $field_name;
  $variables['attributes']['class'][] = $name_class;

  // Add a class to field labels.
  if (!isset($variables['title_attributes']['class'])) {
    $variables['title_attributes']['class'] = [];
  }
  $variables['title_attributes']['class'][] = 'field-label';
  $variables['title_attributes']['class'][] = 'field-label--' . $field_name;
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function hook_form_search_block_form_alter(&$form, $form_state) {
  // Adds a placeholder value to the search form.
  $form['keys']['#attributes']['placeholder'] = t('Search');
}

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function hook_theme_suggestions_field_alter(array &$suggestions, array $variables) {
  // Set custom template suggestions for fields.
  switch ($variables['element']['#field_name']) {
    case 'field_something':
    case 'field_something_else':
      $suggestions[] = 'field__something_or_other';
      break;
  }
}

/**
 * Implements template_preprocess_block().
 */
function hook_preprocess_block(&$variables) {
  // Custom block type helper classes.
  if (!isset($variables['elements']['content']['#block_content'])) {
    return;
  }

  $bundle = $variables['elements']['content']['#block_content']->bundle();
  $bundle_class = str_replace('_', '-', $bundle);

  if (!isset($variables['attributes']['class'])) {
    $variables['attributes']['class'] = [];
  }

  $variables['attributes']['class'][] = Html::cleanCssIdentifier('block--bundle-' . $bundle_class);
}

Thanks, Abby! This might be more obvious if I had a easily available dev environment to test out dsm on at the moment, but I'm curious about the parts reading ->bundle(). Is that some kind of function or method available to certain variables or parts of the render arrays (that I'm guessing returns a list of media types or blocks in the above cases)?

Hey @maxstarkenburg! Yep, it's pretty much exactly as you said - ->bundle() is available on I believe any entity, and will return the machine name of the bundle (i.e. content type, media type, block type, etc.). The official explanation of it is at https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21EntityInterface.php/function/EntityInterface%3A%3Abundle/8.2.x, though it's pretty sparse.