PHP code to place a search bar into the nav menu as a li. Pulls the search bar from search.php.

Search Bar in Nav Menu

/*Wordpress
functions.php*/

add_filter('wp_nav_menu_items','add_search_box', 10, 2);
function add_search_box($items, $args) {
  ob_start();
  get_search_form();
  $searchform = ob_get_contents();
  ob_end_clean();

  $items .= '<li class="navSearch">' . $searchform . '</li>';

  return $items;
}