public function showFile($field = null, $name = null)
    {
        $file = $this->getFilePath($field, $name);
        if (!file_exists($file) || !is_file($file)) {
            throw new NotFoundHttpException;
        }
        header('Content-Type: '. FileHelper::getMimeType($file), true);
        header('Content-Length: ' . filesize($file));
        readfile($file);
    }