Display current parent and its sub-menu only - wordpress

Question

I have a main navigation and all parents have children. Eg:

Page A: About Us
child1
child2

Page B : Our services
Child 3
Child 4

I need to include a horizontal sub-menu on a page. But my problem is, if currently we are on page A, all the child items of page A only to be displayed on page. If we are on Page A, it should looks like:

Page A
Child 1
Child 2

Like this, when we go to Page B, the child of page B only to be displayed.

      <?php 
  $args = array(
   'theme_location'  => '',
   'menu'            => '13',  //nav menu id, which has about-us as a menu.
   'container'       => 'div',
   'container_class' => '',
   'container_id'    => '',
   'menu_class'      => 'menu',
   'menu_id'         => '',
   'echo'            => true,
   'fallback_cb'     => 'wp_page_menu',
   'before'          => '',
   'after'           => '',
   'link_before'     => '',
   'link_after'      => '',
   'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
   'depth'           => 0,
   'walker'          => ''
);
  $menu_items = wp_nav_menu($args);//wp_get_nav_menu_items(13);

I tried writing above code, which resulted in all the parent items with their children.

Can someone help me on this?

In short, I want to get all the children(sub-menu) of About us menu entry.(i.e. I want child1 & child2 as a list with <a> tags)

Answer 1

Please write this code in theme's functions.php

<?php

// add hook
add_filter( 'wp_nav_menu_objects', 'my_wp_nav_menu_objects_sub_menu', 10, 2 );

// filter_hook function to react on sub_menu flag
function my_wp_nav_menu_objects_sub_menu( $sorted_menu_items, $args ) {
  if ( isset( $args->sub_menu ) ) {
    $root_id = 0;
    // find the current menu item
    foreach ( $sorted_menu_items as $menu_item ) {
      if ( $menu_item->current ) {
        // set the root id based on whether the current menu item has a parent or not
      $root_id = ( $menu_item->menu_item_parent ) ? $menu_item->menu_item_parent : $menu_item->ID;
      break;
    }
  }
  // find the top level parent
  if ( ! isset( $args->direct_parent ) ) {
    $prev_root_id = $root_id;
    while ( $prev_root_id != 0 ) {
      foreach ( $sorted_menu_items as $menu_item ) {
        if ( $menu_item->ID == $prev_root_id ) {
          $prev_root_id = $menu_item->menu_item_parent;
          // don't set the root_id to 0 if we've reached the top of the menu
          if ( $prev_root_id != 0 ) $root_id = $menu_item->menu_item_parent;
            break;
          }
        }
      }
    }

    $menu_item_parents = array();
    foreach ( $sorted_menu_items as $key => $item ) {
      // init menu_item_parents
      if ( $item->ID == $root_id ) $menu_item_parents[] = $item->ID;

      if ( in_array( $item->menu_item_parent, $menu_item_parents ) ) {
      // part of sub-tree: keep!
        $menu_item_parents[] = $item->ID;
      } else if ( ! ( isset( $args->show_parent ) && in_array( $item->ID, $menu_item_parents ) ) ) {
      // not part of sub-tree: away with it!
      unset( $sorted_menu_items[$key] );
    }
  }
return $sorted_menu_items;
} else {
  return $sorted_menu_items;
}
}

Then you can display it in your theme using wp_nav_menu (just like you normally would), but also passing in a sub_menu flag to activate the custom sub_menu function:

<?php
wp_nav_menu( array(
  'theme_location' => 'primary',
  'sub_menu' => true
) );
?>

Answer 2

When on a page you first get all the pages, then you can get the current page ID, get the children in an array and loop through this array like this:

<?php
    // First get all the pages in your site
    $wp_query = new WP_Query();
    $all_pages = $wp_query->query(array('post_type' => 'page'));

    // Then get your current page ID and children (out of all the pages)
    $current_page_id = get_the_id();
    $current_page_children = get_page_children($current_page_id, $all_pages);

    // Loop through the array of children pages
    foreach ($current_page_children as $child_page) {
        // Echo whatever you want from the pages
    }
?>

EDIT: This has nothing to do with the structured menus you make in the backend, it has to do with making a page child of another page directly in the page edit section.

Answer 3

This is doing it all

<?php
global $wp_query;
if( empty($wp_query->post->post_parent) ) {
$parent = $wp_query->post->ID;
} else {
$parent = $wp_query->post->post_parent;
} ?>
<?php if(wp_list_pages("title_li=&child_of=$parent&echo=0" )): ?>
<div>
<ul>
<?php wp_list_pages("title_li=&child_of=$parent" ); ?>
</ul>
</div>
<?php endif; ?>

Thanks for all the solutions !