wp_list_categories() Exclude All Categories Except One

Question

Is there a way to exclude all categories except one? I want to show a category and it's sub-categories as a dropdown menu, but the admin might add more subcategories to it so I don't want to limit what they can put in there by just including unique ID's.

So I want to exclude all categories except 1 and it's subcategories. Is this possible with wp_list_categories()?

Answer 1

Try the exclude parameter in the wp_list_categories. That should remove the selected categories and their descendants.

EDIT: Must be getting late; this almost the opposite of what you wanted. To only include one category term in a drop-down menu (and all of its descendants), you can use child_of.

Answer 2

Theres possibly a better way of doing this, but this should work :

 $the_terms = get_terms( 'category', 'child_of=<replace with parent id>' );

 $included_terms = array('<replace with parent id>' );

 if( $the_terms )
 {
      foreach( $the_terms as $the_term )
           $included_terms[] = $the_term->term_id;
 }

 sort( $included_terms );

 wp_list_categories(
      'include' => $included_terms
 );

This way will make sure you don't have to update the list of IDs