class EntityDisplayModeBase

abstract class EntityDisplayModeBase extends ConfigEntityBase implements EntityDisplayModeInterface {
    
    /**
     * The ID of the form or view mode.
     *
     * @var string
     */
    protected $id;
    
    /**
     * The human-readable name of the form or view mode.
     *
     * @var string
     */
    protected $label;
    
    /**
     * The entity type this form or view mode is used for.
     *
     * This is not to be confused with EntityDisplayModeBase::$entityType which is
     * inherited from Entity::$entityType.
     *
     * @var string
     */
    protected $targetEntityType;
    
    /**
     * Whether or not this form or view mode has custom settings by default.
     *
     * If FALSE, entities displayed in this mode will reuse the 'default' display
     * settings by default (e.g. right after the module exposing the form or view
     * mode is enabled), but administrators can later use the Field UI to apply
     * custom display settings specific to the form or view mode.
     *
     * @var bool
     */
    protected $status = TRUE;
    
    /**
     * Whether or not the rendered output of this view mode is cached by default.
     *
     * @var bool
     */
    protected $cache = TRUE;
    
    /**
     * {@inheritdoc}
     */
    public static function sort(ConfigEntityInterface $a, ConfigEntityInterface $b) {
        
        /** @var \Drupal\Core\Entity\EntityDisplayModeInterface $a */
        
        /** @var \Drupal\Core\Entity\EntityDisplayModeInterface $b */
        // Sort by the type of entity the view mode is used for.
        $a_type = $a->getTargetType();
        $b_type = $b->getTargetType();
        $type_order = strnatcasecmp($a_type, $b_type);
        return $type_order != 0 ? $type_order : parent::sort($a, $b);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTargetType() {
        return $this->targetEntityType;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setTargetType($target_entity_type) {
        $this->targetEntityType = $target_entity_type;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        parent::calculateDependencies();
        $target_entity_type = \Drupal::entityTypeManager()->getDefinition($this->targetEntityType);
        $this->addDependency('module', $target_entity_type->getProvider());
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSave(EntityStorageInterface $storage) {
        parent::preSave($storage);
        \Drupal::service('entity_field.manager')->clearCachedFieldDefinitions();
    }
    
    /**
     * {@inheritdoc}
     */
    public static function preDelete(EntityStorageInterface $storage, array $entities) {
        parent::preDelete($storage, $entities);
        \Drupal::service('entity_field.manager')->clearCachedFieldDefinitions();
    }
    
    /**
     * {@inheritdoc}
     */
    protected function urlRouteParameters($rel) {
        $uri_route_parameters = parent::urlRouteParameters($rel);
        if ($rel === 'add-form') {
            $uri_route_parameters['entity_type_id'] = $this->getTargetType();
        }
        return $uri_route_parameters;
    }

}