How to add a menu that belongs to parent blog to all child-blogs?

Question

I want to add a menu that belongs to parent multisite blog to all child-blogs. I need the menu displayed in all child-blogs, I mean the same menu on all multisites blogs. How I can do that?

Answer 1

Use a plugin header to force network activation:

Network: true

Register the menu page on admin_menu and network_admin_menu.

Sample code:

<?php
/**
 * Plugin Name: Network Wide Admin Menu
 * Network: true
 */
add_action( 'admin_menu',         'nwam_add_menu' );
add_action( 'network_admin_menu', 'nwam_add_menu' );

/**
 * Register an admin menu item.
 *
 * @wp-hook admin_menu
 * @wp-hook network_admin_menu
 * @return void
 */
function nwam_add_menu()
{
    add_menu_page(
        'Page Title',
        'Menu Title',
        'exist',
        'nwam',
        'nwam_render'
    );
}
/**
 * Callback to render the menu page.
 *
 * @return void
 */
function nwam_render()
{
    print '<h1>' . $GLOBALS['title'] . '</h1>';
}

The menu will be accessible now on all child sites and on the network management site:

---

In answer to your comment: To add an item to all navigation menus use the code from this answer in a plugin with a header Network: true.

Answer 2

Well, thanks to @toscho ... For your help I found a way to achieve show the primary nav that belongs to parent blog to all child blogs:

/**
 * Plugin Name: Network Primary Nav
 * Network: true
 */

add_filter( 'wp_nav_menu_objects', 'network_primary_nav', 100, 2 );

function network_primary_nav( $menu_items, $args )
{
  global $blog_id;
  $menu_name = 'primary';

  if ( ( $blog_id > 1 ) && $menu_name == $args->theme_location )
  {

    // to parent blog
    switch_to_blog(1);

    $locations = get_nav_menu_locations();

    // get primary nav of parent blog
    if ( isset( $locations[ $menu_name ] ) )
    {
      $menu       = wp_get_nav_menu_object( $locations[ $menu_name ] );
      $menu_items = wp_get_nav_menu_items( $menu->term_id);
    }

    // to child blog
    restore_current_blog();

  }

  return $menu_items;

}