wp_list_pages to show all pages on all sub pages

Question

I have this code to list my parent page and all pages under it on the sidebar. It shows both parent and child pages on first two levels but when I open a third level page, it only shows the current page on the sidebar. How can I modify this to show parent page and all child pages, no matter how many levels of child pages I have.

CODE:

<?php
        if ( $post->post_parent ) {
            $children = wp_list_pages( array(
                'title_li' => '',
                'depth'    => 0,
                'child_of' => $post->post_parent,
                'echo'     => 0
    
            ));
    } else {
        $children = wp_list_pages( array(
            'title_li' => '',
            
            'depth'        => 0,
            'child_of' => $post->ID,
            'echo'     => 0

        ) );
    }

    if ( $children ) : ?>
        <ul class="sideNavigation">
            <?php echo $children; ?>
        </ul>
    <?php endif; ?>

Answer 1

Use this WP function get_pages() and get_page_children()

function get_child_pages( $parent_page_ID ){
    $all_pages = get_pages( array( 'post_type'=> 'page' ) );
    $child_pages = get_page_children( $parent_page_ID, $all_pages );
    if( !empty( $child_pages ) ){
        $html .= '<ul>';
        foreach ( $child_pages as $key => $child_page ) {
            $html .= '<li>'.$child_page->post_title;
            get_child_pages( $child_page->ID );
            $html .= '</li>';
        }
        $html .= '</ul>';
    }
    return $html;
}

function list_pages(){
    $html = '';

    if ( $post->post_parent ) {
        $parent = $post->post_parent;
    }else{
        $parent = $post->ID;
    }

    $parent_pages = get_pages( array( 'parent' => $parent, 'post_type'=> 'page' ) );
    $html.= '<ul>';
    foreach ( $parent_pages as $parent_page ) {
        $html .= '<li>'.$parent_page->post_title;
        $html .= get_child_pages( $parent_page->ID );
        $html .= '</li>';
    }
    $html.= '</ul>';
    return $html;
}
add_shortcode( 'list_pages', 'list_pages' );