WordPressの固定ページ一覧に順序の項目を追加する

function check_post_type_support_page_attr() {
    $all_post_types = get_post_types( array('show_ui' => true ), false );
 
    if ( !isset( $_REQUEST['post_type'] ) ) {
        $edit_post_type = 'post';
    } elseif ( in_array( $_REQUEST['post_type'], array_keys( $all_post_types ) ) ) {
        $edit_post_type = $_REQUEST['post_type'];
    } else {
        wp_die( __('Invalid post type') );
    }
     
    if ( post_type_supports( $edit_post_type, 'page-attributes' ) ) {
        add_filter( 'manage_' . $edit_post_type . '_posts_columns', 'add_menu_order_column' );
        add_action( 'admin_print_styles-edit.php', 'add_menu_order_column_styles' );
        add_filter( 'manage_edit-' . $edit_post_type . '_sortable_columns', 'add_menu_order_sortable_column' );
    }
}
add_action( 'load-edit.php' , 'check_post_type_support_page_attr' );
if ( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
    add_action( 'admin_init', 'check_post_type_support_page_attr' );
}
 
 
function add_menu_order_column( $posts_columns ) {
    $new_columns = array();
    foreach ( $posts_columns as $column_name => $column_display_name ) {
        if ( $column_name == 'date' ) {
            $new_columns['order'] = __( 'Order' );
            add_action( 'manage_pages_custom_column', 'display_menu_order_column', 10, 2 );
            add_action( 'manage_posts_custom_column', 'display_menu_order_column', 10, 2 );
        }
        $new_columns[$column_name] = $column_display_name;
    }
    return $new_columns;
}
 
 
function add_menu_order_sortable_column( $sortable_column ) {
    $sortable_column['order'] = 'menu_order';
    return $sortable_column;
}
 
 
function display_menu_order_column( $column_name, $post_id ) {
    if ( $column_name == 'order' ) {
        $post_id = (int)$post_id;
        $post = get_post( $post_id );
        echo $post->menu_order;
    }
}
 
 
function add_menu_order_column_styles() {
?>
<style type="text/css" charset="utf-8">
.fixed .column-order {
    width: 7%;
    text-align: center;
}
</style>
<?php
}