Add File Form Elements

gistfile1.txt

  /**
   * Adds the configured field from the file entity to form element.
   *
   * @param array $files
   *   Files which fields should be added.
   * @param array $element
   *   Current form element.
   * @param FormStateInterface $form_state
   *   Current state of the form.
   *
   * @return array
   *   The modified form element.
   */
  protected static function addFileEntityFields(
    array $files, array $element, FormStateInterface $form_state) {
    foreach ($files as $fid => $file) {
      // Add fieldset with inline entity fields.
      $element[self::FORM_KEY] = array(
        '#type' => 'fieldset',
        '#title' => t('Inline fields'),
        '#description' => t('Here you can edit custom fields of the file,
         after it has been uploaded.'),
        '#weight' => 10,
        '#parents' => array(self::FORM_KEY, $fid),
      );

      $display = EntityFormDisplay::collectRenderDisplay($file, 'default');
      $display->buildForm($file, $element[self::FORM_KEY], $form_state);
    }

    // Only display fields that are enabled in the widget config.
    foreach (Element::children($element[self::FORM_KEY]) as $field) {
      $config = $element['#' . self::CONFIG_KEY];
      if (isset($config) && empty($config[$field])) {
        $element[self::FORM_KEY][$field]['#access'] = FALSE;
      }
    }

    return $element;
  }