Setting a Default 'Theme Location' When Creating a Menu

Question

I'm trying to create a theme which when activated, sets up a primary navigation, adds the homepage to it and then enables it in the correct location.

Here's what I've got so far:

register_nav_menu('Primary', 'Primary Navigation');

$primary_nav_menu_id = wp_create_nav_menu('Primary');

wp_update_nav_menu_item($primary_nav_menu_id, 0, array(
    'menu-item-title' =>  __('Home'),
    'menu-item-classes' => 'home',
    'menu-item-url' => home_url( '/' ), 
    'menu-item-status' => 'publish'
));

The above creates the menu, adds a link to the homepage but how would I go about automatically assigning this menu a theme location of 'Primary Navigation'?

Is this possible?

Answer 1

You need to first collect the menu locations, then set the primary menu location with the menu id.

// Set the menu to primary menu location
$locations = get_theme_mod( 'nav_menu_locations' );
$locations['primary'] = $primary_nav_menu_id;
set_theme_mod ( 'nav_menu_locations', $locations );

Here I assume 'primary' is theme location referring to 'Primary Navigation'.

Answer 2

The other answer is the short version for this. However, I made a function, that does a bit more. It does this:

• It gets the locations (so the new menu can be added later)
• It gets any menu by the name 'Mobile Menu' and get's the ID for that.
• It sets the 'Mobile Menu' to be active for the display_location for the navigation called nav-mobile
• And then it saves it all.

<?php
add_action( 'init', function() {
  // Variables
  $location_name = 'nav-mobile'; // As it's named in register_nav_menus( ... )
  $menu_name = 'Mobile Menu'; // The name of the menu in the WP backend
  $save_new_locations = false; // To only save, if it isn't set already
  $locations = get_theme_mod( 'nav_menu_locations' ); // Get all nav_locations

  if( ! isset( $locations[ $location_name ] ) ){
    $menus = get_terms( 'nav_menu' ); 
    $menus = array_combine( wp_list_pluck( $menus, 'term_id' ), wp_list_pluck( $menus, 'name' ) ); 
    // Above-written line matches id to menu name, like this:
    // [ 
    //   4129 => 'my-navigation',
    //   4123 => 'my-other-navigation',
    //   ...
    // ]
    // where 4129 and 4123 is the id of the menus 

    $mobile_menu_key = array_search( $menu_name, $menus ); // Finds ID
    if( !empty( $mobile_menu_key ) ){
      $locations[ $location_name ] = $mobile_menu_key;
      $save_new_locations = true;
    }
  }

  if( $save_new_locations ){
    set_theme_mod( 'nav_menu_locations', $locations );
  }
});