public function render()
    {
        $args = $this->buildViewParams();
        if (isset($args['output']))
            $this->output = $args['output'];

        if (!empty($this->view)) {
            return FrontController::getInstance()
                ->view( DirectoryHelper::slashDirname($this->views_dir).$this->view, $args );
        } elseif (isset($this->output)) {
            return $this->output;
        } else {
            throw new RuntimeException("Tool '".get_class($this)."' do not render anything !");
        }
    }