public function PlaceholderGenerator::createPlaceholder

public PlaceholderGenerator::createPlaceholder(array $element)

Turns the given element into a placeholder.

Placeholdering allows us to avoid "poor cacheability contamination": this maps the current render array to one that only has #markup and #attached, and #attached contains a placeholder with this element's prior cacheability metadata. In other words: this placeholder is perfectly cacheable, the placeholder replacement logic effectively cordons off poor cacheability.

Parameters

array $element: The render array to create a placeholder for.

Return value

array Render array with placeholder markup and the attached placeholder replacement metadata.

Overrides PlaceholderGeneratorInterface::createPlaceholder

File

core/lib/Drupal/Core/Render/PlaceholderGenerator.php, line 70

Class

PlaceholderGenerator

Turns a render array into a placeholder.

Namespace

Drupal\Core\Render

Code

public function createPlaceholder(array $element) {
  $placeholder_render_array = array_intersect_key($element, [
    // Placeholders are replaced with markup by executing the associated
    // #lazy_builder callback, which generates a render array, and which the
    // Renderer will render and replace the placeholder with.
    '#lazy_builder' => TRUE,
    // The cacheability metadata for the placeholder. The rendered result of
    // the placeholder may itself be cached, if [#cache][keys] are specified.
    '#cache' => TRUE,
  ]);

  // Generate placeholder markup. Note that the only requirement is that this
  // is unique markup that isn't easily guessable. The #lazy_builder callback
  // and its arguments are put in the placeholder markup solely to simplify<<<
  // debugging.
  $callback = $placeholder_render_array['#lazy_builder'][0];
  $arguments = UrlHelper::buildQuery($placeholder_render_array['#lazy_builder'][1]);
  $token = hash('crc32b', serialize($placeholder_render_array));
  $placeholder_markup = '<drupal-render-placeholder callback="' . Html::escape($callback) . '" arguments="' . Html::escape($arguments) . '" token="' . Html::escape($token) . '"></drupal-render-placeholder>';

  // Build the placeholder element to return.
  $placeholder_element = [];
  $placeholder_element['#markup'] = Markup::create($placeholder_markup);
  $placeholder_element['#attached']['placeholders'][$placeholder_markup] = $placeholder_render_array;
  return $placeholder_element;
}