AutoIncrementingTestItem.php

<?php

namespace Drupal\entity_test\Plugin\Field\FieldType;

use Drupal\Core\Field\Plugin\Field\FieldType\IntegerItem;

/**
 * Defines the 'field_method_invocation_order_test' entity field type.
 *
 * @FieldType(
 *   id = "auto_incrementing_test",
 *   label = @Translation("Auto incrementing test field item"),
 *   description = @Translation("An entity field designed to test the field method invocation order."),
 *   category = @Translation("Number"),
 *   no_ui = TRUE,
 * )
 */
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;
    }

}