Add a class to main menu links

Question

I've searched and found variations of this question but I've never found an answer that seemed to work. I need to add a class to the <li> elements, currently the main menu is rendered like this:

print theme('links__system_main_menu', array(
    'links' => $main_menu,
    'attributes' => array(
        'id' => 'slidemenu',
        'class' => array(
            'links',
            'inline',
            'clearfix'
        )
    ),
    'heading' => t('')
));

As far as I can tell, this only sets up the <ul> element of the main menu, so I was wondering if there's a way to edit the attributes of the 'links' part.

---EDIT---

Alright, I think I solved it. Apparently you can use theme_links__system_main_menu in templates to override the whole thing. I ended up doing this:

function mytheme_links__system_main_menu($variables) {
    $html = '<div id="mainmenu">';
    $html .= '  <ul id="slidemenu" class="clearfix">';

    static $linkClass = 1;

    foreach ($variables['links'] as $link) {                
        $html .= '<li class="themastyle' . $linkClass . '">' . l($link['title'], $link['href'], $link) . '</li>';
        ++$linkClass;
    }

    $html .= '  </ul>';
    $html .= '</div>';

    return $html;
}

Not entirely sure if this is correct Drupal, though it did solve my issue!

Answer 1

print_r($main_menu); each $main_menu items should have this structure:

array(
    'title' => 'xxx',
    'href' => 'xxx',
    'attributes' => array(
        'class' => array('xxx'),
    ),
);

so you can add class to li by altering $main_menu array.

Answer 2

Menu Attributes is another great module that allows you to set class, id, rel and other attributes on either the a or li element.

Answer 3

if your looking for a D8+ fix, the Menu Link Attributes module saves a lot of time. You can specify attributes and classes through a YML file or directly to individual links in Admin Menu UI.

Answer 4

If you don't mind using a existing module, you could also use Menu Names CSS. This module adds the target path of a menu item as a sanitized css-class to the li-item.

A second benefit is, that the module is good template how to put your functionality in a module instead of the template.php file, to increase the re-useability of your code.