Unusual Custom Post 404 problem (NOT a permalink issue)

Question

I seem to have exhausted all the references on this subject, but if this is a duplicate post my apologies.

I am having a problem where ANY custom post page displays the 404.php file's error content, regardless of method of getting there. This includes simply going to something as rudimentary as http://domain.com/?p=123.

I have done the following:

• Flushed permalink settings (though I don't think it's a permalink problem)
• Deleted .htaccess and recreated it by going to settings -> permalinks
• Specifically created a single-[name].php file for any given type
• Disabled all plugins
• Checked for any page/taxonomy name conflicts (still fails even w/ random name)
• Checked server logs for errors (none since troubleshooting began)
• Uploaded entire theme to different WP install

All to no avail.

I have reduced the custom post registration to as simple a function as I can conjure:

add_action('init', 'init_sample');
function init_sample() {
    $args = array(
        'public' => true,
    );
    register_post_type( 'sample' , $args );
}

But neither this nor any other combinations of arguments seem to help.

Even clicking the "View Post" link in admin takes one to a 404 page.

I can, however, retrieve custom posts via query with no problem.

I'm running WP v3.2.1.

If I had to guess, I'd say there's something elsewhere in the theme fouling things up, but I have no idea where to go to find that out - could anyone provide some suggestions on where to even look to troubleshoot this issue?

Answer 1

As soon as I was done asking the question, I went to close functions.php for the night and happened to notice the custom post types were being registered along with other admin-specific features inside an if (is_admin()) { evaluator. Taking them out of that did the trick.

Reasonably enough, it looks like custom posts MUST be registered in a publicly-accessible manner.

There must be some law that, regardless of hours of effort leading up to a Stack Exchange question, the solution will present itself within minutes after it's asked.

Answer 2

Custom Post types are "registered" in code, not in the database (like custom taxonomies to name another example). So wrapping such code in a if ( is_admin() ) statements blends it away from public facing queries as your theme or plugin doesn't tell the public $wp_query object that there's such a thing as your cpt or custom taxonomy. This also means that stuff like the $wp_template_hierarchy won't work if you don't "register" it for every page view.