Two simple functions for getting the ID of next and previous pages (not posts) in Wordpress. Forked from the "Next Page, Not Next Post" plugin by Matt McInvale. http://wordpress.org/plugins/next-page-not-next-post/

README.md

Functions

Next Page: next_page_ID($id) Previous Page: previous_page_ID($id)

$id: The ID of the page you're trying to get the next or previous page for.

Examples

$next_ID = next_page_ID('41);
$previous_ID = previous_page_ID('41);
$next_url = get_permalink($next_ID);

echo '<a href="' . $next_url . '">Next Page</a>';

wp-next-page-id.php

<?php

/* =============================================================
    NEXT PAGE ID
    A function to get the next page's ID.
    $id = ID of the page you want to find the next page for.
 * ============================================================= */

function next_page_ID($id) {

    // Get all pages under this section
    $post = get_post($id);
    $post_parent = $post->post_parent;
    $get_pages_query = 'child_of=' . $post_parent . '&parent=' . $post_parent . '&sort_column=menu_order&sort_order=asc';
	$get_pages = get_pages($get_pages_query);
	$next_page_id = '';

    // Count results
	$page_count = count($get_pages);
	
	for ($p=0; $p < $page_count; $p++) {
	  	// Get the array key for our entry
		if ($id == $get_pages[$p]->ID) break;
	}
	
	// Assign our next key
	$next_key = $p+1;
	
	// If there isn't a value assigned for the previous key, go all the way to the end
	if (isset($get_pages[$next_key])) {
		$next_page_id = $get_pages[$next_key]->ID;
	}

	return $next_page_id;
}


/* =============================================================
    PREVIOUS PAGE ID
    A function to get the previous page's ID.
    $id = ID of the page you want to find the previous page for.
 * ============================================================= */

function previous_page_ID($id) {

    // Get all pages under this section
    $post = get_post($id);
    $post_parent = $post->post_parent;
    $get_pages_query = 'child_of=' . $post_parent . '&parent=' . $post_parent . '&sort_column=menu_order&sort_order=asc';
	$get_pages = get_pages($get_pages_query);
	$prev_page_id = '';

	// Count results
	$page_count = count($get_pages);
	
	for($p=0; $p < $page_count; $p++) {
	  // get the array key for our entry
		if ($id == $get_pages[$p]->ID) break;
	}
	
	// assign our next & previous keys
	$prev_key = $p-1;
	$last_key = $page_count-1;
	
	// if there isn't a value assigned for the previous key, go all the way to the end
	if (isset($get_pages[$prev_key])) {
		$prev_page_id = $get_pages[$prev_key]->ID;
	}

  	return $prev_page_id;
}

?>

Thanks for this. This is a modified version that shows the next parent page when the last child is reached.

function nextPageId($id, $postType) {
	// Get all pages under this section
	$post = get_post($id);
	$post_parent = $post->post_parent;
	$get_pages_query = 'post_type='.$postType.'&child_of=' . $post_parent . '&parent=' . $post_parent . '&sort_column=menu_order&sort_order=asc';
	$pages = get_pages($get_pages_query);

	$breakNext = false;
	foreach($pages as $p){
		if($breakNext) return $p->ID;
		if($p->ID == $id){
			$breakNext = true;
		}
	}

	// looks like it was the last child of this parent, get the next parent
	if($post_parent > 0){
		return nextPageId($post_parent, $postType);
	}

	return -1;
}

Hi could you please help me. I have tried to use a code to do next and previous with shortcodes in function but the ID order of page is not followed...
Could you please tell me how to

1. amend my code to use it with ID order of same category
   or
2. Use your code but with image and category
   Thank you so much for your help. I think it because I used Elementor in wordpress that it messed things up :(

`
add_shortcode( 'prev', 'prev_shortcode' );
add_shortcode( 'next', 'next_shortcode' );
function next_shortcode($atts) {
global $post;
ob_start();
next_post_link( '

%link

', '

', '%title ' . _x( '→', 'Previous post link', 'morphology' ) . '',
true);
$result = ob_get_contents();
ob_end_clean();
return $result;
}

function prev_shortcode($atts) {
global $post;
ob_start();
previous_post_link( '

%link

', '

', '%title ' . _x( '→', 'Previous post link', 'morphology' ) . '',
true );
$result = ob_get_contents();
ob_end_clean();
return $result;
}``