class FormatterBase

abstract class FormatterBase extends PluginSettingsBase implements FormatterInterface, ContainerFactoryPluginInterface {
    
    /**
     * The field definition.
     *
     * @var \Drupal\Core\Field\FieldDefinitionInterface
     */
    protected $fieldDefinition;
    
    /**
     * The formatter settings.
     *
     * @var array
     */
    protected $settings;
    
    /**
     * The label display setting.
     *
     * @var string
     */
    protected $label;
    
    /**
     * The view mode.
     *
     * @var string
     */
    protected $viewMode;
    
    /**
     * Constructs a FormatterBase object.
     *
     * @param string $plugin_id
     *   The plugin ID for the formatter.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The definition of the field to which the formatter is associated.
     * @param array $settings
     *   The formatter settings.
     * @param string $label
     *   The formatter label display setting.
     * @param string $view_mode
     *   The view mode.
     * @param array $third_party_settings
     *   Any third party settings.
     */
    public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings) {
        parent::__construct([], $plugin_id, $plugin_definition);
        $this->fieldDefinition = $field_definition;
        $this->settings = $settings;
        $this->label = $label;
        $this->viewMode = $view_mode;
        $this->thirdPartySettings = $third_party_settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['view_mode'], $configuration['third_party_settings']);
    }
    
    /**
     * {@inheritdoc}
     */
    public function view(FieldItemListInterface $items, $langcode = NULL) {
        // Default the language to the current content language.
        if (empty($langcode)) {
            $langcode = \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)
                ->getId();
        }
        $elements = $this->viewElements($items, $langcode);
        // Field item lists, in particular for computed fields, may carry cacheable
        // metadata which must be bubbled.
        if ($items instanceof CacheableDependencyInterface) {
            (new CacheableMetadata())->addCacheableDependency($items)
                ->applyTo($elements);
        }
        // If there are actual renderable children, use #theme => field, otherwise,
        // let cacheability metadata pass through for correct bubbling.
        if (Element::children($elements)) {
            $entity = $items->getEntity();
            $entity_type = $entity->getEntityTypeId();
            $field_name = $this->fieldDefinition
                ->getName();
            $info = [
                '#theme' => 'field',
                '#title' => $this->fieldDefinition
                    ->getLabel(),
                '#label_display' => $this->label,
                '#view_mode' => $this->viewMode,
                '#language' => $items->getLangcode(),
                '#field_name' => $field_name,
                '#field_type' => $this->fieldDefinition
                    ->getType(),
                '#field_translatable' => $this->fieldDefinition
                    ->isTranslatable(),
                '#entity_type' => $entity_type,
                '#bundle' => $entity->bundle(),
                '#object' => $entity,
                '#items' => $items,
                '#formatter' => $this->getPluginId(),
                '#is_multiple' => $this->fieldDefinition
                    ->getFieldStorageDefinition()
                    ->isMultiple(),
                '#third_party_settings' => $this->getThirdPartySettings(),
            ];
            $elements = array_merge($info, $elements);
        }
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareView(array $entities_items) {
    }
    
    /**
     * Returns the array of field settings.
     *
     * @return array
     *   The array of settings.
     */
    protected function getFieldSettings() {
        return $this->fieldDefinition
            ->getSettings();
    }
    
    /**
     * Returns the value of a field setting.
     *
     * @param string $setting_name
     *   The setting name.
     *
     * @return mixed
     *   The setting value.
     */
    protected function getFieldSetting($setting_name) {
        return $this->fieldDefinition
            ->getSetting($setting_name);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        // By default, formatters are available for all fields.
        return TRUE;
    }

}