Display flash messages in Symfony2

gistfile1.twig

{# Check if we got a session without creating one #}
{% if app.request.hasPreviousSession %}
    {# Check if we got some flash messages #}
    {% if app.session.flashbag.peekAll()|length > 0 %}
        <div id="flash">
            {# Loop all types of flash messages #}
            {% for type, flashMessages in app.session.flashbag.all() %}
                {# For all flash messages with this type #}
                {% for idx, flashMessage in flashMessages %}
                    <div class="flash-item flash-type-{{ type }}">
                            {{ flashMessage|trans|trim }}
                    </div>
                {% endfor %}
            {% endfor %}
        </div>
    {% endif %}
{% endif %}