How to grab a specific page of content from paginated post?

Question

In my case I've got to create articles where each article has a custom, unchanging "header" part far too rich for the title and the excerpt (it's to contain image, media etc), and then a few different pages of content. I've decided to do this using <!--nextpage--> to keep it lightweight and easy for whoever will create the pages - treat the first page as the unchanging header and attach page 2, 3, 4 under a fixed set of links - an custom menu generated in that category, replacing standard pagination "Page 1 2 3 4" links.

In order to do that, I'll have to call the_content() twice; once for page 1, and once for whichever page is chosen through the dedicated menu. Except I have no clue how to make the_content() extract n-th page, other than through appending /n/ to the URL.

Is there some variable, function, plugin, modification to the code that lets me extract a specific page of paginated post?

Answer 1

nextpage pagination is a bit odd. You will have to parse the post content. This should do it.

function get_nth_page($n=0,$content='') {
  if (empty($content)) {
    global $post;
    $content = $post->post_content;
  }
  if (empty($content)) {
    return false;
  }
  $content = str_replace("\n<!--nextpage-->\n", '<!--nextpage-->', $content);
  $content = str_replace("\n<!--nextpage-->", '<!--nextpage-->', $content);
  $content = str_replace("<!--nextpage-->\n", '<!--nextpage-->', $content);
  $pages = explode('<!--nextpage-->', $content);
  if (isset($pages[$n])) {
    return $pages[$n];
  }
}

You can pass $content explicitly or it will try to grab the global $post variable.