template-functions-get-columns.php

<?php

/**
 * Fetch all columns for a particular list table.
 */
function acp_loaded()
{
    /**
     * The "List Screen ID" can be found by opening the screen options in the top-right corner of the
     * admin columns settings page. Enable the "List screen ID" by clicking the checkbox next to it.
     * The list screen ID will now be visible in the right sidebar.
     * @var string $list_screen_id
     */
    $list_screen_id = "<LIST SCREEN ID GOES HERE>"; // e.g. '5e84e8302794f'

    /**
     * @var AC\Column[] $columns
     */
    $columns = ac_get_columns($list_screen_id);
}

add_action('wp_loaded', 'acp_loaded');