Wordpress - 在所述子页面上显示父页面的子页面

Question

I have the following hierarchical order:

Parent Page
     Child Page 1
     Child Page 2
     Child Page 3

I use the following PHP snippet to show all child pages on the parent page in a side navigation:

wp_list_pages('title_li=&child_of='.$post->ID.'&echo=1');

Now to my question:

How can I modify the snippet that it also displays the side navigation on the child pages? Somehow: 'Go to your parent page, collect all child pages and display it where you are, on a child page'.

Thanks for reading!

Answer 1

wp_list_pages('title_li=&child_of='.$post->post_parent.'&echo=1');

This snippet will return the current page and its siblings. However this will only return the children of the current page's parent. If you need to get pages for a deeply nested hierarchy you should use:

global $post;
    /* Get an array of Ancestors and Parents if they exist */
$parents = get_post_ancestors( $post->ID );
    /* Get the top Level page->ID count base 1, array base 0 so -1 */ 
$id = ($parents) ? $parents[count($parents)-1]: $post->ID;
wp_list_pages('title_li=&child_of='.$id.'&echo=1');