WordPress Admin: When placing a Custom Post Type as a submenu of a parent menu, the parent menu link is being overridden by the CPT

Question

I register a Custom Post Type, and I don\'t want it to have its own menu, instead I want to place it as a submenu of an existing admin menu item called my-custom-parent-pa

Answer 1

You also can simply set 'show_in_menu' in custom post type args to $menu_slug that you set in add_menu_page() that you want to set the CPT as sub menu of and set the priority of admin_menu function to 9 or lower. For example:

First, create a new top-level menu page, with priority set to 9 or lower (it's a must):

add_action( 'admin_menu', 'settings_menu' ), 9 );

function settings_menu() {

    add_menu_page( __( 'Page Title' ), 'Menu Title', 'manage_options', 'menu_slug', show_page_callback() );
}

function show_page_callback() {

    // show the settings page, plugin homepage, etc.
}

Then create custom post type with 'show_in_menu' arg set to menu_slug that we just set in settings_menu() function.

add_action( 'init', 'create_post_type' );

function create_post_type() {

register_post_type('my_custom_post_type',
    array(
        'labels' => array(              
            'name'               => __('Books', 'mcpt'),
            'singular_name'      => __('Book', 'mcpt'),
        ),
        'supports' => array('title', 'editor'),
        'public' => true,
        'show_in_menu' => 'menu_slug',
    );
}

Hope it helps.

Answer 2

Place a Custom-Post-Type in an submenu of an existing parent page

According to the Codex, this is a known and expected behavior:

Note: When using 'some string' to show as a submenu of a menu page created by a plugin, this item will become the first submenu item, and replace the location of the top level link.

Source: https://codex.wordpress.org/Function_Reference/register_post_type#Arguments (See the "show_in_menu" section)

Here is the end of the quote which offers a solution:

If this isn't desired, the plugin that creates the menu page needs to set the add_action priority for admin_menu to 9 or lower.

So this is quite simple to solve. However in my case I couldn't change the priority of the parent page because it is generated by a third-party library. Therefore I came up with this solution:

// Move the "example_cpt" Custom-Post-Type to be a submenu of the "example_parent_page_id" admin page.
add_action('admin_menu', 'fix_admin_menu_submenu', 11);
function fix_admin_menu_submenu() {

    // Add "Example CPT" Custom-Post-Type as submenu of the "Example Parent Page" page
    add_submenu_page('example_parent_page_id', 'Example CPT', 'Example CPT', 'edit_pages' , 'edit.php?post_type=example_cpt');
}

Please note the priority 11, and also when registering the Custom-Post-Type I set the "show_in_menu" parameter to false, so we can add it in the menu manually via add_submenu_page as shown above.

---

Properly set the Custom-Post-Type submenu entry as "active"

Now, the above solution works fine, however when creating/editing a post of the "example_cpt" Custom-Post-Type, it is not set as active and the submenu is not unfolded. Here is how to make sure that it is set as active, as well as the submenu in which it resides is properly set as active when creating/editing a post of the "example_cpt" Custom-Post-Type:

// Set the "example_parent_page_id" submenu as active/current when creating/editing a "example_cpt" post
add_filter('parent_file', 'fix_admin_parent_file');
function fix_admin_parent_file($parent_file){
    global $submenu_file, $current_screen;

    // Set correct active/current menu and submenu in the WordPress Admin menu for the "example_cpt" Add-New/Edit/List
    if($current_screen->post_type == 'example_cpt') {
        $submenu_file = 'edit.php?post_type=example_cpt';
        $parent_file = 'example_parent_page_id';
    }
    return $parent_file;
}

---

Fine-tuning: Rename the first submenu entry

Furthermore, I also wanted the first menu entry of my submenu to be named differently from the parent name. By default, and using the code above, this is what we have:

- Example Parent Page
-- Example Parent Page
-- Example CPT

So as you can see, the first menu entry of the submenu is a duplicate of the parent menu, and this is the default WordPress behavior. I wanted to rename this duplicate entry to something different, much like WordPress does with the default menus (for example "Posts" and the submenu entry "All Posts" which both point to the same page but are named differently).

Here is how to rename the first submenu entry:

add_action('admin_menu', 'rename_first_submenu_entry', 11);
function rename_first_submenu_entry() {

    // Rename first submenu entry (duplicate of parent menu) from "Example Parent Page" to "Submenu Text"
    add_submenu_page('example_parent_page_id', 'Example Parent Page', 'Submenu Text', 'edit_pages' , 'example_parent_page_id');

}

Please note the priority 11, so it is renamed after it has been created. And now we have:

- Example Parent Page
-- Submenu Text
-- Example CPT

Please note that "Submenu Text" points to the same location as "Example Parent Page".

Answer 3

can't say, what's exactly the reason, but it seems wordpress redirects to the first submenu-item.

So you have to create a new sub-menu-item with the same contents of your parent-menu-item.

add_action('admin_menu', 'my_admin_menu');

function my_admin_menu() {
    global $submenu;
    add_menu_page('My Menu', 'My Menu', 'administrator', 'my-menu', 'callback_func');

    $parent = array('My Menu', 'administrator', 'my-menu', 'My Menu'); // new submenu-itm
    $submenu['my-menu'] = fix_menu($submenu['my-menu'], $parent); // adds the new submenu-item at beginning of 'my-menu'-item
}

function fix_menu($submenu) {
    array_unshift ($submenu, $parent);
    return $submenu;
}

Hope it works for you.