Global page ID variable empty error

Question

I am creating theme and I have a need to create global variables within theme functions.php file.

Currently I am doing it like this:

/**
 * Setup globals
 */
global $nb_id, $nb_page;

$nb_id = get_the_ID();
// Prepare & set fallback
$globals_array  = array(
    'nb_id'     => $nb_id,
    'nb_page'   => array(
        'id'    => $nb_id,
        'end'   => 'front',
        'name'  => 'home',
        'type'  => 'page'
    )
);

// Set each value from globals array as global $var;
foreach ($globals_array as $name => $value) {
    global $$name;
    $$name              = $value;
    $_GLOBALS[$name]    = $value;

    // Set user view of page
    if($name == 'nb_page'){
        if(is_admin()) $$name['end']    = 'back';
        $$name['name']      = $nb_pagenow;
        // Determine if is page or single post
        if(is_single()) $$name['type']  = 'single';

        $_GLOBALS[$name]    = $$name;
    }
}

The issue is that I cannot retrieve front-end current page/post ID using get_the_ID(), $wp_query->get_queried_object_id() or even $wp->public_query_vars with page_id.

Currently all the scenarios return these values:

1. get_the_ID() = null
2. $wp_query->get_queried_object_id() = 0
3. $wp->public_query_vars = "page_id" [34]=> string(5) "error"

Does anyone have any idea why I am having this issue? Am I doing something wrong? Maybe there is another way to call front-end page/post data within functions.php!?

Answer 1

After some research and thanks to @Milo for pointing out about using hooks after wp is set, I finnaly got it working. Indeed I had to call it as soon as wp has queried and generated some post/page data;

This is my final solution, where I used add_action( 'template_redirect', 'nb_setup_globals' );

Here is the final code:

/**
 * Setup globals
 */
global $nb_id, $nb_view, $nb_page;
function nb_setup_globals(){
    global $post, $nb_id, $nb_view, $nb_page;

    // Set default vars for globals
    $nb_id = $post->ID;
    $nb_view        = 'front';
    $nb_post_name   = 'index';
    $nb_post_type   = 'post';

    // Post type page
    if(is_page()){
        if(nb_get_template_slug()){
            $nb_post_name = nb_get_template_slug();
        }else{
            $nb_post_name = 'page';
        }
        $nb_post_type = 'page';
    }

    // Post type post / custom post
    if(is_single()){
        $nb_post_name = $post->post_type;
    }

    // View
    if(is_admin()) $nb_view = 'back';

    // Before globals set default vars one last time
    $globals_array  = array(
        'nb_page'   => array(
            'id'    => $nb_id,
            'name'  => $nb_post_name,
            'type'  => $nb_post_type
        )
    );

    /**
     * Let the magin GLOBALS be registered
     */
    foreach ($globals_array as $name => $value) {
        global $$name;

        $$name = $value;
    }
}
add_action( 'template_redirect', 'nb_setup_globals' );

This also works in back-end (post/page edit etc.). Although haven't testet it fully.