AutoIncrementingTestItem.php

<?php

declare (strict_types=1);
namespace Drupal\entity_test\Plugin\Field\FieldType;

use Drupal\Core\Field\Attribute\FieldType;
use Drupal\Core\Field\Plugin\Field\FieldType\IntegerItem;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Defines the 'field_method_invocation_order_test' entity field type.
 */
class AutoIncrementingTestItem extends IntegerItem {
  
  /**
   * {@inheritdoc}
   */
  public function preSave() {
    parent::preSave();
    $this->value = static::getIncrementedFieldValue();
  }
  
  /**
   * Gets an incremented field value.
   *
   * @return int
   *   The incremented field value.
   */
  private static function getIncrementedFieldValue() {
    static $cache = 0;
    return ++$cache;
  }

}