您可以将其添加到菜单构建器中，例如..

You can add it in your menu builder like..

$menu = $this->factory->createItem('root', array(
    'childrenAttributes'    => array(
        'class'             => 'foo',
    ),
));

更新

我刚刚收到有关此问题的通知，并找到了另一种方法，尽管它需要您使用自定义模板来实现.

I just got a notification about this and found another way although it requires you to use a custom template to achieve it.

在您的自定义模板中，您需要覆盖 list 块，例如..

In your custom template you need to override the list block like..

{% block list %}
    {% if item.hasChildren and options.depth is not sameas(0) and item.displayChildren %}
        {% import 'knp_menu.html.twig' as knp_menu %}
        <ul{{ knp_menu.attributes(listAttributes|merge({'class': [
                options.rootClass is defined ? options.rootClass : '',
                listAttributes.class is defined ? listAttributes.class : ''
            ]|join(' ')
        })) }}>
            {% set options = options|merge({'rootClass': '' }) %}
            {{ block('children') }}
        </ul>
    {% endif %}
{% endblock %}

在这个而不是使用 knp_menu.attributes(listAttributes) 中，您传入一个带有动态生成的 listAttributes.class 值的数组.该属性是通过将 option.rootClass(如果存在)与 listAttributes.class(如果存在)作为 listAttributes.class 值来生成的.

In this rather than use knp_menu.attributes(listAttributes) you pass in a array with your on-the-fly generated listAttributes.class value. This attribute is generate by joining option.rootClass (if it exists) with listAttributes.class (if it exists) as the listAttributes.class value.

option.rootClass 值在使用后使用 {% set options = options|merge({'rootClass': '' }) %} 这样它就不会被添加到每个子菜单中.

The option.rootClass value is reset to '' after use using {% set options = options|merge({'rootClass': '' }) %} so that it is not added to every sub-menu.

这将允许您使用...呈现菜单

This will allow you to render your menu using..

{{ knp_menu_render('main', {'rootClass': 'foo' }) }}