Wordpress: displaying an error message - hook admin_notices fails on wp_insert_post_data or publish_post

Question

I\'m adding validation so if a post is in a particular category, it needs certain Custom Fields to be set.

This should be easy hooking wp_insert_post_data

Answer 1

Wordpress doesn't use sessions, and if register_globals is on it will clear the $_SESSION array.

Wordpress passes it's messages along using a message integer in the URL, an array of messages is then defined in the relevant edit-[type]-form.php file in the wp-admin folder. I think you could probably append your own variable to the redirect and then get that in your admin_notices hook function. Take a look at the edit-[type]-form.php files to get an idea of how this might work.

Answer 2

if($out = $_SESSION['admin_notices']) { 
      $_SESSION["admin_notices"] = ""; 
      echo $out; 
}

This condition is always TRUE so it always reset your $_SESSION['admin_notices'] var

Answer 3

You can simply do like WordPress do : using transients like this :

function set_post_pending($data, $postarr) {
    // If it's not valid...
        $error = "You are missing some Custom Fields.";
        set_transient( get_current_user_id().'missingfield', $error );
        $data['post_status'] = 'pending';
    return $data;
}
add_filter('wp_insert_post_data', 'set_post_pending',1,2);

function show_admin_notice() {
    if($out = get_transient( get_current_user_id().'missingfield' ) ) {
        delete_transient( get_current_user_id().'missingfield' );
        echo "<div class=\"error\"><p>$out</p></div>";
    }
    // return false; // nothing to return here
}
add_action('admin_notices', "session_admin_notice");

ps : avoid $_SESSION in WordPress, thx