DummyAjaxItem.php

<?php

namespace Drupal\image_module_test\Plugin\Field\FieldType;

use Drupal\Core\Field\FieldItemBase;
use Drupal\Core\Field\FieldStorageDefinitionInterface;
use Drupal\Core\TypedData\DataDefinition;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Defines a dummy field containing an AJAX handler.
 *
 * @FieldType(
 *   id = "image_module_test_dummy_ajax",
 *   label = @Translation("Dummy AJAX"),
 *   description = @Translation("A field containing an AJAX handler."),
 *   category = @Translation("Field"),
 *   default_widget = "image_module_test_dummy_ajax_widget",
 *   default_formatter = "image_module_test_dummy_ajax_formatter"
 * )
 */
class DummyAjaxItem extends FieldItemBase {
    
    /**
     * {@inheritdoc}
     */
    public static function schema(FieldStorageDefinitionInterface $field_definition) {
        return [
            'columns' => [
                'value' => [
                    'type' => 'varchar',
                    'length' => 255,
                ],
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function isEmpty() {
        return empty($this->get('value')
            ->getValue());
    }
    
    /**
     * {@inheritdoc}
     */
    public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
        $properties['value'] = DataDefinition::create('string')->setLabel(new TranslatableMarkup('Dummy string value'));
        return $properties;
    }

}