Adding custom slugs: parent-page/username/child-page/

Question

I'm in a bit of a muddle understanding how I can change my $_GET variables into a 'slug'. I already have a setup of a parent-page/child-page using wp_insert_post. BUT! I want to add a variable in-between to create the setup of parent-page/?username=bob/child-page.

I was looking at add_rewrite_rule to change my format from index.php?page_id=PAGE_ID&username=bob to /users/bob/about/.

I've tried this:

public static function add_rewrite(){
    $page=get_page_by_title('users');
    add_rewrite_rule('^users/([a-zA-Z0-9]+)/?','index.php?page_id='.$page->ID.'&username=$matches[1]','top');
}
//quickly to show how called.
add_action('init',array(__CLASS__,'add_rewrite');

This doesn't work but I was hoping to at least achieve users/username/ so that I can figure out how to add my child page later.

Sorry if I'm confusing!!

EDIT!!

I managed to sort out my errors. This is what I've achieved so far:

public static function add_vars($public_query_vars){
    $public_query_vars[]='username';
    return$public_query_vars;
}
public static function addRewriteRule(){
    $page=get_page_by_title('users');
    //add_rewrite_rule('^leaf/([0-9]+)/?', 'index.php?page_id=$matches[1]','top');
    add_rewrite_rule('^users/([^/]+)/?$','index.php?page_id='.$page->ID.'&username=$matches[1]','top');
}

So now I can access get_query_var('username'); But! I'm still unable to get my child page for the parent page, any ideas? Thanks in advance!

Answer 1

Found the solution!

I was trying to over complicate things. The best method I've come up with is:

    $users=get_page_by_title('users');
    $about=get_page_by_title('about');
    add_rewrite_rule('^users/([^/]*)$','index.php?page_id='.$users->ID.'&username=$matches[1]','top');
    add_rewrite_rule('^users/([^/]*)/about/?','index.php?page_id='.$about->ID.'&username=$matches[1]','top');

Haven't come up with errors yet, haven't tested yet!