[WordPress] A function used to retrieve all of the post IDs that are being represented by a single menu.

acme-get-posts-for-menu.php

<?php 
function acme_get_posts_for_menu( $menu_name ) {

  // Read all of the navigation menu locations
  $locations = get_nav_menu_locations();

  // Grab the specific menu identified by the specified menu name.
  $menu = wp_get_nav_menu_object( $locations[ $menu_name ] );
  $menu_items = wp_get_nav_menu_items( $menu->term_id );

	// Grab all of the post IDs that are represented in this menu
  $post_ids = array();
  foreach( $menu_items as $post ) {
    $post_ids[] = $post->object_id;
  }

  return $post_ids;

}

get-post-content-for-menu.php

<?php
$args = array(
  'post_type'           => array( 'post', 'page', 'video' ),
  'post__in'            => acme_get_posts_for_menu( 'my-custom-menu' ),
  'post_status'         => 'publish',
  'ignore_sticky_posts' => 1,
  'orderby'             => 'menu_order'
);
$my_query = new WP_Query( $args );

if ( $my_query->have_posts() ) {
  
  while( $my_query->have_posts() ) {
    $my_query->the_post();
    /* Display post content here */
  }
  wp_reset_postdata();
  
}