Creating PHP previous page button on first page in WordPress - php

Question

I have this PHP code that works excellent in displaying arrows to previous/next pages of WordPress child pages:
<?php // Button Code for Prev and Next Page
$my_wp_query = new WP_Query();
$all_wp_pages = $my_wp_query->query(
array('post_type' => 'page'));
$portfolio = get_page_by_title('Services');
$args = array (
'child_of' => $portfolio->ID,
'sort_order' => 'asc',
'post_type' => 'page'
);
$portfolio_children = get_pages( $args );
$pages = array();
foreach ($portfolio_children as $page) {
$pages[] += $page->ID;
}
$current = array_search($post->ID, $pages);
$prevID = $pages[$current-1];
$nextID = $pages[$current+1];
?>
<div class="navigation">
<?php if (!empty($prevID)) { ?>
<div class="previousarrow">
<a href="<?php echo get_permalink($prevID); ?>" title="<?php echo get_the_title($prevID); ?>">
<img src="<?php bloginfo('url');?>/wp-content/uploads/2016/06/previousbutton.png">
</a>
</div>
<?php }
if (!empty($nextID)) { ?>
<div class="nextarrow">
<a href="<?php echo get_permalink($nextID); ?>" title="<?php echo get_the_title($nextID); ?>">
<img src="<?php bloginfo('url');?>/wp-content/uploads/2016/06/nextbutton.png">
</a>
</div>
<?php } ?>
</div>
Problem is that on the first and last pages, I can't get it to show the previous/next button to go to the 'last or first' page of the child pages.
Example
A (parent)
1 (child page 1)
2 (child page 2)
3 (child page 3)
I want the previous option on page 1 to go to page 3 and vice versa but I can't figure that out. Any help is appreciated.

Answer 1

The buttons are not appearing because of the php if parameters, which eliminates the previous arrow on page 1 and next arrow on page 3 because it recognizes them as empty. One way around this would be to remove the if clauses and use if statements to define your prevID and nextID variables, or you can simply add else statements after each if statement defines the previous/next buttons to be shown. However, both of these solutions are temporary, as you would require the number of pages in order to implement them, which is subject to change. Instead, use this code to ensure this feature will stay intact even if you add additional pages:
<?php if (empty($prevID)) { $firstpage = $pages[$current]; }
if (empty($nextID)) {$lastpage = $pages[$current]; }
This will define the value of the first and last pages, and can simply be inserted after you define prevID and nextID. Now simply add php else statements like so:
</div> <?php }
else { ?>
<div class="previousarrow>
<a href="<?php echo get_permalink($lastpage); ?>"
title="<?php echo get_the_title($lastpage); ?>">
<img src="<?php bloginfo('url');?>
/wp-content/uploads/2016/06/previousbutton.png"></a></div>
<?php }
This block of code would be inserted after your first div class, as the previous arrow should navigate to the last page when no previous page exists. Do the exact same after the second div class, replacing the lastpage variable with the firstpage one we created. Hope this helps!