Modifying render arrays in preprocess hooksfor Drupal 8 , 9 , 10 , and 11

Render arrays are a powerful feature in Drupal, allowing developers to manipulate the structure and content before rendering HTML. By using preprocess hooks, you gain control over these arrays, enabling you to dynamically alter content presentation in a structured manner.

Understanding Render Arrays

In Drupal, render arrays are associative arrays that represent HTML content. They contain key-value pairs, where keys may define properties, attributes, and content. Render arrays ensure that the content is processed correctly with respect to caching, lazy loading, and security considerations.

Benefits of Using Render Arrays

• Structure: Maintain a clean separation between content logic and presentation.
• Flexibility: Easily manipulate HTML output at different stages of the rendering process.
• Performance: Maximize caching and minimize overhead by delaying the rendering when possible.

Preprocess Hooks

Preprocess hooks are functions used to modify variables and render arrays before they are passed to Twig templates. These hooks provide an opportunity to inject custom data, alter array structures, or change attributes before the final HTML output is generated.

Step 1: Identify the Preprocess Hook

The naming convention for preprocess hooks follows THEME_preprocess_HOOK. For nodes, it's THEME_preprocess_node(). Replace THEME with your active theme's name.

Step 2: Implement the Hook

Add the preprocess hook to your theme’s .theme file. Here's an example using a custom theme named mytheme:

// In mytheme.theme
/**
 * Implements hook_preprocess_HOOK() for node templates.
 *
 * Adds a custom class and additional element to the node render array.
 */
function mytheme_preprocess_node(array &$variables) {
  // Add a custom class to the node.
  $variables['attributes']['class'][] = 'my-custom-node-class';

  // Add a new renderable element.
  $variables['content']['new_element'] = [
    '#markup' => '
Custom content goes here.
',
    '#weight' => 100,
  ];
}

Here, a new class is added to the node's attributes array, and a new element with custom markup is appended to the node's content section using the #markup and #weight properties.

Step 3: Clear Cache

Always remember to clear the cache to apply changes in Drupal. You can use drush cr or the admin UI under Configuration -> Performance -> Clear all caches.

Step 4: Test the Output

Review your site to ensure the changes are correctly applied. Inspect elements to verify that the custom class is present and that the new content renders as expected.

Considerations for Using Preprocess Hooks

• Maintain Clear Logic: Ensure logic within preprocess functions remains simple and readable.
• Component Separation: Use hooks to keep theming logic separate from core modules and dependencies.
• Debugging: Utilize tools like Kint to inspect render arrays and view their content before applying modifications.

Summary

Mastering render arrays through preprocess hooks in Drupal allows you to fine-tune content presentation with precision. By dynamically altering render arrays, you maintain flexibility in how your content is displayed, ensuring a seamless integration between logic and presentation, all while optimizing performance.