ChangedFieldItemList.php

<?php

namespace Drupal\Core\Field;

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Session\AccountInterface;

/**
 * Defines an item list class for changed fields.
 */
class ChangedFieldItemList extends FieldItemList {
    
    /**
     * {@inheritdoc}
     */
    public function defaultAccess($operation = 'view', AccountInterface $account = NULL) {
        // It is not possible to edit the changed field.
        return AccessResult::allowedIf($operation !== 'edit');
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasAffectingChanges(FieldItemListInterface $original_items, $langcode) {
        // When saving entities in the user interface, the changed timestamp is
        // automatically incremented by ContentEntityForm::submitForm() even if
        // nothing was actually changed. Thus, the changed time needs to be
        // ignored when determining whether there are any actual changes in the
        // entity.
        return FALSE;
    }

}