add_submenu_page() link missing 'admin.php?' prefix

Question

I have two plugins - one is the "primary" plugin called "SmartPost" and I'm trying to extend it with another plugin called "SmartPost E-mails". So, in other words, "SmartPost E-mails" extends and depends on "SmartPost" to exist and load before the e-mails plugin does.

Within the SmartPost plugin, I have the following admin menu creation functions:

class sp_admin{
   add_action( 'admin_menu', array('sp_admin', 'sp_admin_add_template_page') );
   add_action( 'admin_menu', array('sp_admin', 'sp_admin_add_category_page') );

    function sp_admin_add_template_page() {
        add_menu_page( SP_PLUGIN_NAME, SP_PLUGIN_NAME, 'edit_dashboard', 'smartpost', array('sp_admin', 'sp_template_page'), null, null );
    }

    function sp_admin_add_category_page(){
        add_submenu_page( 'smartpost', 'Settings', 'Settings', 'edit_dashboard', 'sp-cat-page', array('sp_admin', 'sp_settings_page') );
    }
}

In my "SmartPost E-mails" plugin, I want to add a submenu to the SmartPost plugin page, so I have the following code:

class SP_Email_Admin_Page{

    function __construct(){
        add_action( 'admin_menu', array($this, 'sp_add_email_admin_page') );
    }

    function sp_add_email_admin_page(){
        if( ( is_plugin_active( "smartpost-templates/smartpost.php" ) ) && defined( "SP_PLUGIN_NAME" ) ){
            add_submenu_page( 'smartpost', 'E-mail Settings', 'E-mail Settings', 'edit_dashboard', 'sp-email-settings', array($this, 'sp_render_email_admin_page') );
        }
    }

    function sp_render_email_admin_page(){
        ?>
        <p>Hello World</p>
        <?php
    }
}
$sp_admin_page = new SP_Email_Admin_Page();

This results in strange behavior as described in this post. The submenu is added, but is linked improperly (the 'admin.php?' prefix is missing). I think it has to do with the fact that the add_submenu_page is defined outside of the same scope as where the parent menu page was defined - but I'm not sure why that would be a factor. This begs two questions: 1) Why is this happening and 2) how do plugins such as WooCommerce allow 3rd party plugin developers to create sub-menus for the WooCommerce admin page when the add_submenu_page() is most likely defined outside of the same scope as the parent WooCommerce menu page ?

Answer 1

I renamed the "SmartPost E-mail" plugin folder so it loads after the "SmartPost" plugin - I think. I'm pretty sure this "weird" behavior has to do with the order in which plugins are loaded. If a plugin is loaded before its "parent" plugin, then the weird behavior mentioned above will probably happen.

Answer 2

Within your sp_add_email_admin_page, try duplicating the add_menu function before adding the add_submenu_page

function sp_add_email_admin_page(){
    if( ( is_plugin_active( "smartpost-templates/smartpost.php" ) ) && defined( "SP_PLUGIN_NAME" ) ){
        add_menu_page( SP_PLUGIN_NAME, SP_PLUGIN_NAME, 'edit_dashboard', 'smartpost', array('sp_admin', 'sp_template_page'), 'dashicons-menu', null );
        add_submenu_page( 'smartpost', 'E-mail Settings', 'E-mail Settings', 'edit_dashboard', 'sp-email-settings', array($this, 'sp_render_email_admin_page') );
    }
}

Answer 3

Try this code:

class SP_Email_Admin_Page
{

    function __construct()
    {
        add_action( 'admin_menu', array($this, 'sp_add_email_admin_page') );
    }

    function sp_add_email_admin_page()
    {
        if( ( is_plugin_active( "smartpost-templates/smartpost.php" ) ) && defined( "SP_PLUGIN_NAME" ) )
        {
            add_submenu_page( 'smartpost', 'E-mail Settings', 'E-mail Settings', 'theme-option', 'sp-email-settings', array($this, 'sp_render_email_admin_page') );
        }
    }

    function sp_render_email_admin_page()
    {
        ?>
        <p>Hello World</p>
        <?php
    }
}
$sp_admin_page = new SP_Email_Admin_Page();

Answer 4

Just make sure to use a higher priority for your action hooks:

add_action( 'admin_menu', array( 'sp_admin', 'sp_admin_add_template_page' ), 999 );