Print links to children or prev/next siblings according to current page's position in nav menu. Useful when paired with: https://gist.github.com/smhmic/fb6432a9326fcb72a0b8ecfc596c5761

. pfx_wp_show_pagelinks_from_navmenu (Print links to children or prev&next siblings according to current page's position in nav menu) .php

<?php
/**
 * Print links to children or prev/next siblings according to current page's position in nav menu.
 * To be used as template tag.
 * 
 * Useful when paired with: https://gist.github.com/smhmic/fb6432a9326fcb72a0b8ecfc596c5761
 * 
 */
add_action('after_content','pfx_wp_show_pagelinks_from_navmenu');
function pfx_wp_show_pagelinks_from_navmenu( $menu_id, $exclude_post_ids = array() ){
    if( ! is_page() )
        return;

    $post_id = get_the_ID();
    $menuItems = wp_get_nav_menu_items( $menu_id );
    
    $exclude = $exclude_post_ids;/*array( 
        '38', // MRF
        '26', // Contact
        '359', // Calendar
        '465', // Submit to Blog
        '537', // Useful Links
    );*/
    
    $found = $url = $title = $parent = $prev = $next = false;

    if( !in_array( $post_id, $exclude ) ) {
        foreach( $menuItems as $menuItem ) {
            if( $post_id == $menuItem->object_id ) {
                //pfx_dump( $menuItem );
                $this_parent = $menuItem->menu_item_parent;
                if( !$this_parent ) {
                    break;
                }
                $found = true;
                if( $this_parent === $parent ) {
                    $prev =
                        '<a class="prev-page page-link" href="'
                        .$url
                        .'"><i class="fa fa-chevron-left"></i> '
                        .$title
                        .'</a>';
                }
            } elseif( !in_array( $menuItem->object_id, $exclude ) ) {
                $parent = $menuItem->menu_item_parent;
                $url    = $menuItem->url;
                $title  = $menuItem->title;
                if( $found ) {
                    if( $this_parent === $parent ) {
                        $next =
                            '<a class="next-page page-link" href="'
                            .$url
                            .'">'
                            .$title
                            .' <i class="fa fa-chevron-right"></i></a>';
                    }
                    break;
                }
            }
        }
    }
    
    // show child page links according to nav

    $found = $url = $title = $parent = $curr_menu_obj_id = false;
    $children = array();

    foreach( $menuItems as $menuItem ) {
        if( $found ) {
            if( $curr_menu_obj_id == $menuItem->menu_item_parent ) {
                $children[] = $menuItem;
            }
        } 
        else {
            if( $post_id == $menuItem->object_id ) {
                //pfx_dump( $menuItem );
                $found = true;
                $curr_menu_obj_id = $menuItem->ID;
            }
        }
    }
    
    if( $children || $prev || $next ){
        echo '<div class="page-links">';
        foreach( $children as $c ){
            echo '<a class="child-page page-link" href="'.$c->url.'">'.$c->title.'</a>';
            //echo '<div><a class="child-page page-link" href="'.$c->url.'">'.$c->title.'</a></div>';
        }

        if( $prev ) {
            echo $prev;
        }
        if( $next ) {
            echo $next;
        }
        echo '</div>';
    }
    
}