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I'm using responsive images (single img tag with srcset and sizes attributes). My content editors can manipulate the displayed size of the image with a custom field on a shared parent entity. Therefore I can't meaningfully use the sizes field from the responsive image module, because my editors can set the image size from 10% of a fixed container up to 100vw on per paragraph level.

I know how to preprocess the sizes attributes, but I don't know how to get to my shared parent entity, which holds the field determining the size of the image's parent container:

function template_preprocess_responsive_image(&$variables) {
  // pseudocode: don't know how to this
  $imageField = $variables['whatever'];
  $parentParagraph = $imageField->getParentMediaEntity()->getParentParagraphEntity();
}

My question is how do I get the parent paragraph entity as written above in pseudocode?

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    Could you check the value of $variables['#item']? It seems that the viewElements function of the field formatter adds $file->_referringItem to the render array, which I'd expect to be the parent entity. – Neograph734 Sep 11 '17 at 11:05
  • 1
    Yes, but this is another hook, template_preprocess_responsive_image_formatter() and you get the field item, which parent is the field and the grandparent is the paragraph. – 4k4 Sep 11 '17 at 11:54
  • 1
    ... which you can get with this shortcut FieldItemBase::getEntity: $parentEntity = $imageField->getEntity(); – 4k4 Sep 11 '17 at 12:56
  • OK, seems I've had the wrong starting point with hook_preprocess_responsive_image(). Using hook_preprocess_responsive_image_formatter() and $entity = $variables['item']->getEntity(); I'm getting my media entity. Thanks for your help, I'll post an answer as soon as I have a working code. – Hudri Sep 11 '17 at 13:21
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Here is the the "real" code counterpart to the pseudecode from the question:

function THEMENAME_preprocess_responsive_image_formatter(array &$variables) {
  // get the imagefield's parent entity
  $fieldParent = $variables['item']->getEntity();

  // this line is only needed if using media entities (= entity references)
  // must disable entity view caching to work correctly
  $fieldParent = $fieldParent->_referringItem->getEntity();

  // get the image width from the custom field
  $myImgSizes = $fieldParent->get('field_image_size')->getString();
  // can't change attribute here => store it temporarily
  $variables['responsive_image']['#attributes']['data-overridesizes'] = $myImgSizes;
}

function THEMENAME_preprocess_responsive_image(array &$variables) {
  //override sizes attribute with my calculated value
  if (key_exists('data-overridesizes', $variables['img_element']['#attributes'])) {
    $variables['img_element']['#attributes']['sizes'] = $variables['img_element']['#attributes']['data-overridesizes'];
    unset($variables['img_element']['#attributes']['data-overridesizes']);
  }
}

If using media (=entity references) you also have to disable view cache for entites (see this question)

function MODULENAME_entity_view(&$build, $entity, $display, $view_mode) {
  if ($entity->getEntityTypeId() == 'media' && $entity->bundle() == 'image' && $view_mode == 'my_uncached_viewmode'){
    unset($build['#cache']['keys']);
  }
}
  • Answer is not yet fully correct, when using the same media on different paragraphs, I always get the first paragraph referencing the media, instead of the real parent. – Hudri Sep 12 '17 at 11:27
  • Then you have to disable caching. You can do this for all media entities in the entity type definition by adding render_cache = FALSE or create a view mode and add to the config yaml file cache: false. – 4k4 Sep 15 '17 at 7:25
  • Thanks, already found another question dealing with the cache issue, posted my final, working code – Hudri Sep 15 '17 at 13:30
  • Thank you so much for this information! I didn't realize that _referringItem is unreliable due to caching. Turns out it was the source of my bug and setting cache: false within the config yaml file for my view mode fixed it. It appears there is an open issue for this on Drupal.org: drupal.org/project/drupal/issues/2908449 I agree with the issue creator that accessing parent entities is really important so I hope somebody works on it. It's way out of my league. – maskedjellybean Oct 3 '18 at 0:34

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