Paginated WordPress posts with an option to view as a single post

paginated-posts-advanced.php

<?php 
/*
----------------------------------------------------------------------------------------------------------
On themes that already have built in support, all you have to do is add <!--nextpage--> via the html 
editor on WordPress where you want to add a new page to your post. If your theme doesn't have 
intrisic support already built in for this then you can add it with one line:

<?php wp_link_pages(); ?>

References:
http://codex.wordpress.org/Styling_Page-Links
http://www.nathanrice.net/blog/creating-a-blog-page-with-paging/
http://wordpress.stackexchange.com/questions/32119/single-page-view-for-paginated-posts
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/*

// Once you have this set up, you can also add a single page view option with the code below:

/*
 * Custom query variable for single-page views on multi-page posts
 *
 * ------  Add this to your functions.php file -------
 */
 function somename_parameter_queryvars( $qvars ) {
    $qvars[] = 'all';
    return $qvars;
}
add_filter( 'query_vars', 'somename_parameter_queryvars' );

/*
 * ------  Replace your the_content() call with lines 29-40 -------
 */ 
 
// check to see if there is pagination and if the single page view is loaded or not
  global $wp_query;
  $no_pagination = false;
  if ( isset( $wp_query->query_vars['all'] ) ) {
    $no_pagination = $wp_query->query_vars['all'];
  }
  if( $no_pagination ) {
    echo apply_filters( 'the_content', $post->post_content ); 
    $page=$numpages+1;
  } else {
    the_content('Read the rest of this entry');
  }


/*
 * ------  Add lines 48-52 where you want to display the link to view as one page -------
 */
 
// display a link to the single page
 global $numpages;
 if ( is_singular() && $numpages > 1 ) { ?>
    <a href="<?php echo add_query_arg( array( 'all' => '1'), get_permalink() ); ?>" title="single-page view">View on one page</a>
 }