wp_list_categories() with attachment post types

Question

I'm working on a pictures gallery, where there is no 'regular' post, only images with several custom taxonomies, some of them being hierarchical.

I use wp_list_categories() to display hierarchical lists of terms and that works fine provided I set the hide_empty parameter to 0. However, I would like to display only terms that have pictures, or whose descendants have pictures. But I can't find a way to use hierarchical instead of hide_empty, probably because the function looks for terms attached to regular posts.

Is there a way to change its behaviour and make it look for post-type='attachment' or whatever, so I could list only terms related to published pictures?

Thanks for helping.

Answer 1

When you register your taxonomy, set the update_count_callback argument to _update_generic_term_count. This will count all objects associated to taxonomy terms so you don't need to use hide_empty.

$args = array(
    // your other taxonomy arguments here
    'update_count_callback' => '_update_generic_term_count'
);
register_taxonomy( 'your-taxonomy', array( 'attachment' ), $args );