Wordpress Flatsome主题'pre_get_posts'动作挂钩不修改查询

Question

I'm working a Wordpress site that was built by another developer using the Flatsome theme.

I'm trying to modify the search query to include the post types: 'attachment' and 'page' using the following query:

function cia_search_filter($query) {
  if ( !is_admin() && $query->is_main_query() ) {
    if ($query->is_search) {
      $query->set('post_type', array( 'post', 'attachment', 'page' ) );
    }
  }
}

add_action('pre_get_posts','cia_search_filter');

If I var_dump $query->is_main_query() and $query->is_search both return false.

Is this specific to this theme and is there a reason why this doesn't work?