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1. tech-otaku
   Member
   Posted 1 year ago #

   I'm trying to understand what the call to apply filters is doing in this piece of code from the WP_Widget_Categories class in wp-includes/default-widgets.php.

   $cat_args['title_li'] = '';
   wp_list_categories(apply_filters('widget_categories_args', $cat_args));

   My understanding is that the value of $cat_args is being passed to all the functions associated with the widget_categories_args tag and that this association is made using add_filter('widget_categories_args', filter_function).

   However, I don't think my understanding can be correct as I can't find any reference to add_filter('widget_categories_args', filter_function) anywhere within the WP code.

   It seems I've searched everywhere but I'm just not getting it. Could someone shed a little light on how filters work in general.

   Many, many thanks in advance. Steve.

2. Mark / t31os
   Moderator
   Posted 1 year ago #

   apply_filters sets up a filter hook, it doesn't necessarily mean any filters exist for that hook, which is why you aren't able to find any references to add_filter('widget_categories_args',.

   An example filter.
   

   add_filter('widget_categories_args','list_cats_args_filter');
   
   function list_cats_args_filter( $cat_args ) {
       $cat_args['title_li'] = 'My filter provided title';
       return $cat_args;
   }

3. tech-otaku
   Member
   Posted 1 year ago #

   Thanks for clarifying that Mark. I think I've got it.

   Regards, Steve.

4. Mark / t31os
   Moderator
   Posted 1 year ago #

   You're welcome.. :)

   Further examples can be found here.
   http://codex.wordpress.org/Plugin_API/Hooks_2.0.x

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