ManagedFile::valueCallback

public static ManagedFile::valueCallback(&$element, $input, FormStateInterface $form_state)

public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
  // Find the current value of this field.
  $fids = !empty($input['fids']) ? explode(' ', $input['fids']) : [];
  foreach ($fids as $key => $fid) {
    $fids[$key] = (int) $fid;
  }
  $force_default = FALSE;

  // Process any input and save new uploads.
  if ($input !== FALSE) {
    $input['fids'] = $fids;
    $return = $input;

    // Uploads take priority over all other values.
    if ($files = file_managed_file_save_upload($element, $form_state)) {
      if ($element['#multiple']) {
        $fids = array_merge($fids, array_keys($files));
      }
      else {
        $fids = array_keys($files);
      }
    }
    else {
      // Check for #filefield_value_callback values.
      // Because FAPI does not allow multiple #value_callback values like it
      // does for #element_validate and #process, this fills the missing
      // functionality to allow File fields to be extended through FAPI.
      if (isset($element['#file_value_callbacks'])) {
        foreach ($element['#file_value_callbacks'] as $callback) {
          $callback($element, $input, $form_state);
        }
      }

      // Load files if the FIDs have changed to confirm they exist.
      if (!empty($input['fids'])) {
        $fids = [];
        foreach ($input['fids'] as $fid) {
          if ($file = File::load($fid)) {
            $fids[] = $file->id();
            // Temporary files that belong to other users should never be
            // allowed.
            if ($file->isTemporary()) {
              if ($file->getOwnerId() != \Drupal::currentUser()->id()) {
                $force_default = TRUE;
                break;
              }
              // Since file ownership can't be determined for anonymous users,
              // they are not allowed to reuse temporary files at all. But
              // they do need to be able to reuse their own files from earlier
              // submissions of the same form, so to allow that, check for the
              // token added by $this->processManagedFile().
              elseif (\Drupal::currentUser()->isAnonymous()) {
                $token = NestedArray::getValue($form_state->getUserInput(), array_merge($element['#parents'], array('file_' . $file->id(), 'fid_token')));
                if ($token !== Crypt::hmacBase64('file-' . $file->id(), \Drupal::service('private_key')->get() . Settings::getHashSalt())) {
                  $force_default = TRUE;
                  break;
                }
              }
            }
          }
        }
        if ($force_default) {
          $fids = [];
        }
      }
    }
  }

  // If there is no input or if the default value was requested above, use the
  // default value.
  if ($input === FALSE || $force_default) {
    if ($element['#extended']) {
      $default_fids = isset($element['#default_value']['fids']) ? $element['#default_value']['fids'] : [];
      $return = isset($element['#default_value']) ? $element['#default_value'] : ['fids' => []];
    }
    else {
      $default_fids = isset($element['#default_value']) ? $element['#default_value'] : [];
      $return = ['fids' => []];
    }

    // Confirm that the file exists when used as a default value.
    if (!empty($default_fids)) {
      $fids = [];
      foreach ($default_fids as $fid) {
        if ($file = File::load($fid)) {
          $fids[] = $file->id();
        }
      }
    }
  }

  $return['fids'] = $fids;
  return $return;
}