public function addFileToSet($f_id)
    {
        $app = Application::getFacadeApplication();
        if (is_object($f_id)) {
            $f = $f_id;
            if ($f instanceof FileEntity) {
                $file = $f;
                $fileVersion = $file->getApprovedVersion();
            } else {
                $fileVersion = $f;
                $file = $fileVersion->getFile();
            }
            $f_id = (int) $file->getFileID();
        } else {
            $f_id = (int) $f_id;
            $em = $app->make(EntityManagerInterface::class);
            $file = $em->find(FileEntity::class, $f_id);
            $fileVersion = $file->getApprovedVersion();
        }
        if ($file === null) {
            $result = null;
        } else {
            $file_set_file = File::createAndGetFile($f_id, $this->fsID);
            $fe = new \Concrete\Core\File\Event\FileSetFile($file_set_file);
            $director = $app->make(EventDispatcherInterface::class);
            $director->dispatch('on_file_added_to_set', $fe);
            if ($fileVersion !== null && $this->shouldRefreshFileThumbnails('add')) {
                $fileVersion->refreshThumbnails(false);
            }
            $result = $file_set_file;
        }

        return $result;
    }