Can't filter wp_get_attachment_link

Question

Can't figure out why this won't work:

function my_get_attachment_link($html){
    $postid = get_the_ID();
    $html = str_replace('<a','<a rel="shadowbox['.$postid.']"',$html);
    return $html;
}
add_filter('wp_get_attachment_link','my_get_attachment_link',10,1);

Just trying to hook up all the images on a single post view to a lightbox script.

FYI, this didn't work either: http://wordpress.mfields.org/2010/thickbox-for-wordpress-gallery/#highlighter_196509

What could be jamming it up?

Answer 1

Your code only works if you are actually calling wp_get_attachment_link() somewhere in your template. If you're not calling the function, then the apply_filters() inside the function will never get called, and therefore your code will have nothing into which to hook.