Drupal6: In theme_preprocess_page(&$vars), where do $vars come from? (How to manipulate breadcrumb)

Question

I want to remove the breadcrumb when it's just one entry ("Home"). I'm in my theme's theme_preprocess_page(&$vars) function. $vars['breadcrumb'] is available, but it's just HTML. This is a bit to clumsy to work with. I'd rather get it as an array of items in the breadcrumb list, and do something like this:

if (count($breadcrumb) == 1) {
    unset($breadcrumb);
}

Where does $vars come from? How can I override the code creating it originally?

Answer 1

A $vars array is passed on between all preprocess functions. In case of the _preprocess_page functions, most of the values in $vars are created in template_preprocess_page (see http://api.drupal.org/api/function/template_preprocess_page/6). In that function, you'll see:

  $variables['breadcrumb']        = theme('breadcrumb', drupal_get_breadcrumb());

Here, drupal_get_breacrumb returns an array of breadcrumb elements, which is then themed by the theme_breadcrumb() function (or its override).

The easiest way to get what you want is to override the theme_breadcrumb function. To do that, you take the original theme_breadcrumb function (http://api.drupal.org/api/function/theme_breadcrumb/6), copy it to your template.php, replace 'theme' in the function name with the name of your theme and alter the code so it looks like this:

function THEMENAME_breadcrumb($breadcrumb) {
  if (count($breadcrumb) > 1) { // This was:  if (!empty($breadcrumb))
    return '<div class="breadcrumb">'. implode(' » ', $breadcrumb) .'</div>';
  }
}

For a better understanding of Drupal theme overrides and preprocess functions, see About overriding themable output and Setting up variables for use in a template (preprocess functions).