Exclude categories from list (wp_list_categories)

Question

I'm trying to exclude categories from a function-based category list. I browsed and researched here a lot, but couldn't find a solution. Here's the code I use in my sidebar:

 <ul class="side-cat-img"> <li> 
<?php $args = array();
$args['show_last_updated'] = true;
$args['show_count'] = true;
$args['title_li'] = '';
$args['walker'] = new CategoryThumbnail_Walker;

wp_list_categories($args); ?>
</li>  
</ul> 

I want to exclude a few categories, so I used this code:

<?php wp_list_categories('exclude=4,7&title_li='); ?>

Result: The categories were really excluded, but the function didn't work properly anymore.

The function is supposed to pull out a screencap of each category to display. Once I excluded categories, the screenshots didn't show up anymore.

Here's the function code:

class CategoryThumbnail_Walker extends Walker_Category {

    // A new element has been stumbled upon and has ended
    function end_el( &$output, $category, $depth, $args ) {
        // Output the standard link ending
        parent::end_el( &$output, $category, $depth, $args );

        // Get one post
        $posts = get_posts( array(
            // ...from this category
            'category' => $category->cat_ID,
            'numberposts' => 10
        ) );

        // we'll record the seen images here
        if ( !isset($this->images_seen) ) $this->images_seen = array();

        foreach ( $posts as $post ) {
            // Get its thumbnail and append it to the output
            $featured = get_the_post_thumbnail( $post->ID, 'latestpost-thumb', null );
            // have we already seen this image?
            if ( in_array($featured, $this->images_seen) ) continue;
            else {
                $this->images_seen []= $featured;
 $post_cats = get_the_category($post->ID);
$output .= '<li><a href="http://zoomingjapan.com/category/'.$post_cats[0]->slug.'" title="Category Name">'.$featured.'</a></li>'; 
                break;
            }
        }
    }
}

Any ideas how I can change the code to exclude categories without destroying what the function is supposed to do?

Thanks a lot in advance!

Answer 1

This...

<?php wp_list_categories('exclude=4,7&title_li='); ?>

... does not include your Walker. Why didn't you just add that exclude the same way you added the others?

$args = array();
$args['show_last_updated'] = true;
$args['show_count'] = true;
$args['title_li'] = '';
$args['exclude'] = '4,7';
$args['walker'] = new CategoryThumbnail_Walker;

wp_list_categories($args);