我正在尝试修改一个旧主题，但我被这段代码卡住了

$post_type = \'portfolio\' == get_post_type() ? \'portfolio\' : \'post\';

if ( ! themify_check( "setting-{$post_type}_nav_disable" ) ) :

    $in_same_cat = themify_check( "setting-{$post_type}_nav_same_cat" )? true: false;
    $this_taxonomy = \'post\' == get_post_type() ? \'category\' : get_post_type() . \'-category\';
    $previous = get_previous_post_link( \'<span class="prev">%link</span>\', \'<span class="arrow">\' . _x( \'&laquo;\', \'Previous entry link arrow\',\'themify\') . \'</span> %title\', $in_same_cat, \'\', $this_taxonomy );
    $next = get_next_post_link( \'<span class="next">%link</span>\', \'<span class="arrow">\' . _x( \'&raquo;\', \'Next entry link arrow\',\'themify\') . \'</span> %title\', $in_same_cat, \'\', $this_taxonomy );

    if ( ! empty( $previous ) || ! empty( $next ) ) : ?>

        <div class="post-nav clearfix">
            <?php echo $previous; ?>
            <?php echo $next; ?>
        </div>
        <!-- /.post-nav -->

    <?php endif; // empty previous or next

endif; // check setting nav disable

这一部分具体。目前它列出了我所有的文章，但我不知道如何只列出类别id1 2 3

$this_taxonomy = \'post\' == get_post_type() ? \'category\' : get_post_type() . \'-category\';

add_action( \'pre_get_posts\', \'my_allowed_cats\' );
function my_allowed_cats( $query ){

  $post_type = get_post_type();

  if( $post_type == \'post\' || $post_type == \'portfolio\' ){

    // Use category ids
    $allowed_cats = array(
      1,
      2,
      3,
    );

    $query->set( \'category__in\', $allowed_cats );

  }

}