Populate wordpress menu with link to custom field value (file download)

Question

I have an additional menu that appears on some single.php pages. To this menu I would like to add an li with a link to a PDF which is uploaded to the post by a custom field (advanced custom fields helps with this).

I found a snippet on how to add todays date to my menu, and thought I could maybe use this as a starting point. However I´m not good enough coder to know where to go from here. I would appreciate some help with it!

This is the snippet I´m starting with: http://pastebin.com/xHHxuHdQ

I need to make it display this instead:

<a href="<?php the_field('mcf_uppsagning-pdf'); ?>">Uppsägning</a>

I cant just replace it though and I dont know the syntax enough to know how to modify it. Please help :)

Thanks

Answer 1

Try this:

// Filter wp_nav_menu() to add additional links and other output
add_filter('wp_nav_menu_items','add_pdf_to_menu', 10, 2);
function add_pdf_to_menu( $items, $args ) {
    if( $args->theme_location == 'extra-menu')  {

        $pdf = get_post_meta( get_the_ID(), 'mcf_uppsagning-pdf', true );
        if ( $pdf )
            $items .=  '<li><a href="' . wp_get_attachment_url( $pdf ) .  '">Uppsägning</a></li>';

    }
    return $items;
}

Essentially because you're in the context of the single page get_the_ID() will return the id for the post/page you're on. If that doesn't work try using get_queried_object_id() in place of get_the_ID().

EDIT: changed the above code to return the attachment permalink.