AggregatorTitleFormatter.php

<?php

namespace Drupal\aggregator\Plugin\Field\FieldFormatter;

use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\FormatterBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;

/**
 * Plugin implementation of the 'aggregator_title' formatter.
 *
 * @FieldFormatter(
 *   id = "aggregator_title",
 *   label = @Translation("Aggregator title"),
 *   description = @Translation("Formats an aggregator item or feed title with an optional link."),
 *   field_types = {
 *     "string"
 *   }
 * )
 */
class AggregatorTitleFormatter extends FormatterBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        $options = parent::defaultSettings();
        $options['display_as_link'] = TRUE;
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form = parent::settingsForm($form, $form_state);
        $form['display_as_link'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Link to URL'),
            '#default_value' => $this->getSetting('display_as_link'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $elements = [];
        if ($items->getEntity()
            ->getEntityTypeId() == 'aggregator_feed') {
            $url_string = $items->getEntity()
                ->getUrl();
        }
        else {
            $url_string = $items->getEntity()
                ->getLink();
        }
        foreach ($items as $delta => $item) {
            if ($this->getSetting('display_as_link') && $url_string) {
                $elements[$delta] = [
                    '#type' => 'link',
                    '#title' => $item->value,
                    '#url' => Url::fromUri($url_string),
                ];
            }
            else {
                $elements[$delta] = [
                    '#markup' => $item->value,
                ];
            }
        }
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        return ($field_definition->getTargetEntityTypeId() === 'aggregator_item' || $field_definition->getTargetEntityTypeId() === 'aggregator_feed') && $field_definition->getName() === 'title';
    }

}