er_viewmode.module

<?php

/**
 * Implements hook_ctools_plugin_directory().
 */
function er_viewmode_ctools_plugin_directory($module, $plugin) {
  if ($module == 'entityreference') {
    return 'plugins/' . $plugin;
  }
}

/**
 * Implements hook_field_widget_form_alter().
 */
function er_viewmode_field_widget_form_alter(&$element, &$form_state, $context) {
  $field = $context['field'];
  $instance = $context['instance'];
  if (er_viewmode_supported_field_widget($field)) {
    $item = isset($context['items'][$context['delta']]) ? $context['items'][$context['delta']] : NULL;
    $target_type = $field['settings']['target_type'];
    $view_modes = er_viewmode_get_view_modes($field, $instance);

    $instance = $context['instance'];
    if (in_array($instance['widget']['type'], array(
      'entityreference_autocomplete',
      'options_select',
      'options_buttons'
    ))) {
      $element['view_mode'] = array(
        '#type' => 'select',
        '#title' => 'View Mode',
        '#title_display' => 'invisible',
        '#options' => $view_modes,
        '#default_value' => isset($item) ? $item['view_mode'] : 'full',
        '#weight' => 10,
        '#id' => 'view-mode-' . $context['delta'],
      );
    }
  }
}

/**
 * Fetches view_modes based of the field and instance.
 *
 * @param $field array - the field definition
 * @param $instance array - the field instance definition
 * @param $ignore_whitelist boolean - if TRUE it will return the full list of available view modes.
 * @return array - list of view modes
 */
function er_viewmode_get_view_modes($field, $instance, $ignore_whitelist = FALSE) {
  $target_type = $field['settings']['target_type'];
  $entity_info = entity_get_info($target_type);
  $view_modes = array('full' => 'Default');
  foreach ($entity_info['view modes'] as $view_key => $view_mode) {
    if ($ignore_whitelist || !empty($field['settings']['handler_settings']['behaviors']['er_viewmode_behavior']['enabled_viewmodes'][$view_key])) {
      $view_modes[$view_key] = $view_mode['label'];
    }
  }

  if (!$ignore_whitelist) {
    drupal_alter('er_viewmode_get_view_modes', $view_modes, $field, $instance);
  }

  return $view_modes;
}

/**
 * Check if a field is supported by inline entity form view mode
 *
 * @param $field array - definition of a field
 * @return bool - true if the given field is a supported field.
 */
function er_viewmode_supported_field_widget($field) {
  return $field['type'] == 'entityreference' && isset($field['settings']['handler_settings']['behaviors']['er_viewmode_behavior']) && $field['settings']['handler_settings']['behaviors']['er_viewmode_behavior']['status'] == 1;
}

/**
 * Implements hook_field_formatter_settings_form().
 */
function er_viewmode_field_formatter_settings_form($field, $instance, $view_mode, $form, &$form_state) {
  $element = entityreference_field_formatter_settings_form($field, $instance, $view_mode, $form, $form_state);
  if (er_viewmode_supported_field_widget($field)) {
    unset($element['view_mode']);
    $element['view_mode'] = array(
      '#type' => 'markup',
      '#markup' => '<p>' . t('View modes are selected per referenced entity') . '</p>',
    );
  }
  return $element;
}

/**
 * Implements hook_field_formatter_settings_summary().
 */
function er_viewmode_field_formatter_settings_summary($field, $instance, $view_mode) {
  return entityreference_field_formatter_settings_summary($field, $instance, $view_mode);
}

/**
 * Overwrite entityreference modules field_formatter implementation.
 *
 * @todo research less invasive way of archiving this.
 *
 * Implements hook_field_formatter_info_alter().
 */
function er_viewmode_field_formatter_info_alter(&$info) {
  $info['entityreference_entity_view']['module'] = 'er_viewmode';
}

/**
 * Implements hook_field_formatter_prepare_view().
 */
function er_viewmode_field_formatter_prepare_view($entity_type, $entities, $field, $instances, $langcode, &$items, $displays) {
  return entityreference_field_formatter_prepare_view($entity_type, $entities, $field, $instances, $langcode, $items, $displays);
}

/**
 * Implements hook_field_formatter_view().
 */
function er_viewmode_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display) {
  if (!er_viewmode_supported_field_widget($field)) {
    return entityreference_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display);
  }
  $result = array();
  $settings = $display['settings'];

  // Rebuild the items list to contain only those with access.
  foreach ($items as $key => $item) {
    if (empty($item['access'])) {
      unset($items[$key]);
    }
  }

  switch ($display['type']) {
    case 'entityreference_entity_view':
      foreach ($items as $delta => $item) {
        // Protect ourselves from recursive rendering.
        static $depth = 0;
        $depth++;
        if ($depth > 20) {
          throw new EntityReferenceRecursiveRenderingException(t('Recursive rendering detected when rendering entity @entity_type(@entity_id). Aborting rendering.',
            array(
              '@entity_type' => $entity_type,
              '@entity_id' => $item['target_id']
            )));
        }

        $entity = clone $item['entity'];
        unset($entity->content);
        $result[$delta] = entity_view($field['settings']['target_type'],
          array($item['target_id'] => $entity), $item['view_mode'],
          $langcode, FALSE);

        if (empty($settings['links']) && isset($result[$delta][$field['settings']['target_type']][$item['target_id']]['links'])) {
          $result[$delta][$field['settings']['target_type']][$item['target_id']]['links']['#access'] = FALSE;
        }
        $depth = 0;
      }
      break;
  }

  return $result;
}

/**
 * Implements hook_uuid_node_features_export_render_alter().
 */
function er_viewmode_uuid_node_features_export_render_alter(&$export, $node, $module) {
  $fields = uuid_features_get_field_items_iterator($export, 'node', 'entityreference');
  foreach ($fields as $field_name => &$field_languages) {
    foreach ($field_languages as $language => &$field_values) {
      foreach ($field_values as $i => &$field_value) {
        $field_info = field_info_field($field_name);
        // If er_viewmode behavior is being used
        // and the uuid_features module wrongly turned the view mode into a UUID
        // change the view mode back to its original value.
        if (
          !empty($field_info['settings']['handler_settings']['behaviors']['er_viewmode_behavior'])
            && (!empty($field_value['view_mode']) && uuid_is_valid($field_value['view_mode']))
        ) {
          $field_value['view_mode'] = $node->{$field_name}[$language][$i]['view_mode'];
        }
      }
    }
  }
}