ComputedTestCacheableStringItemList.php

<?php

namespace Drupal\entity_test\Plugin\Field;

use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Field\FieldItemList;
use Drupal\Core\TypedData\ComputedItemListTrait;

/**
 * Item list class for computed cacheable string field.
 */
class ComputedTestCacheableStringItemList extends FieldItemList {
    use ComputedItemListTrait;
    
    /**
     * {@inheritdoc}
     */
    protected function computeValue() {
        
        /** @var \Drupal\entity_test\Plugin\Field\FieldType\ComputedTestCacheableStringItem $item */
        $item = $this->createItem(0, 'computed test cacheable string field');
        $cacheability = (new CacheableMetadata())->setCacheContexts([
            'url.query_args:computed_test_cacheable_string_field',
        ])
            ->setCacheTags([
            'field:computed_test_cacheable_string_field',
        ])
            ->setCacheMaxAge(800);
        $item->get('value')
            ->addCacheableDependency($cacheability);
        $this->list[0] = $item;
    }

}