protected function setMessageFileManager($message, $severity, $once = false)
    {
        if ($once) {
            $this->session->setMessage($message, $severity, 'file_manager_messages');
        } else {
            $messages = $this->getData("messages.$severity", array());
            $messages[] = $message;
            $this->setData("messages.$severity", $messages);
        }
    }