WordPress Walker Menu for Bootstrap

bootstrap-walker-menu.php

<?php
// Custom Walker Class for Bootstrap Menu
add_action( 'after_setup_theme', 'bootstrap_setup' );
if ( ! function_exists( 'bootstrap_setup' ) ):
  function bootstrap_setup(){
    class Bootstrap_Walker_Nav_Menu extends Walker_Nav_Menu {
      function start_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat( "\t", $depth );
        $output    .= "\n$indent<ul class=\"dropdown-menu\">\n";
      }
      function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';
        $li_attributes = '';
        $class_names = $value = '';
        $classes = empty( $item->classes ) ? array() : (array) $item->classes;
        $classes[] = ($args->has_children) ? 'dropdown' : '';
        $classes[] = ($item->current || $item->current_item_ancestor) ? 'active' : '';
        $classes[] = 'menu-item-' . $item->ID;
        $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args ) );
        $class_names = ' class="' . esc_attr( $class_names ) . '"';
        $id = apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args );
        $id = strlen( $id ) ? ' id="' . esc_attr( $id ) . '"' : '';
        $output .= $indent . '<li' . $id . $value . $class_names . $li_attributes . '>';
        $attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
        $attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
        $attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
        $attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';
        $attributes .= ($args->has_children)      ? ' class="dropdown-toggle" data-toggle="dropdown"' : '';
        $item_output = $args->before;
        $item_output .= '<a'. $attributes .'>';
        $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
        $item_output .= ($args->has_children) ? ' <b class="caret"></b></a>' : '</a>';
        $item_output .= $args->after;
        $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
      }
      function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {
        if ( !$element )
          return;
        $id_field = $this->db_fields['id'];
        //display this element
        if ( is_array( $args[0] ) ) 
          $args[0]['has_children'] = ! empty( $children_elements[$element->$id_field] );
        else if ( is_object( $args[0] ) ) 
          $args[0]->has_children = ! empty( $children_elements[$element->$id_field] ); 
        $cb_args = array_merge( array(&$output, $element, $depth), $args);
        call_user_func_array(array(&$this, 'start_el'), $cb_args);
        $id = $element->$id_field;
        // descend only when the depth is right and there are childrens for this element
        if ( ($max_depth == 0 || $max_depth > $depth+1 ) && isset( $children_elements[$id]) ) {
          foreach( $children_elements[ $id ] as $child ){
            if ( !isset($newlevel) ) {
              $newlevel = true;
              //start the child delimiter
              $cb_args = array_merge( array(&$output, $depth), $args);
              call_user_func_array(array(&$this, 'start_lvl'), $cb_args);
            }
            $this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output );
          }
            unset( $children_elements[ $id ] );
        }
        if ( isset($newlevel) && $newlevel ){
          //end the child delimiter
          $cb_args = array_merge( array(&$output, $depth), $args);
          call_user_func_array(array(&$this, 'end_lvl'), $cb_args);
        }
        //end this element
        $cb_args = array_merge( array(&$output, $element, $depth), $args);
        call_user_func_array(array(&$this, 'end_el'), $cb_args);
      }
    }
  }
endif;

header.php

<nav role="navigation" id="navbar-main">
			<div class="navbar navbar-inverse navbar-fixed-top">
				<div class="container">
					<!-- .navbar-toggle is used as the toggle for collapsed navbar content -->
					<div class="navbar-header">
						<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-responsive-collapse">
							<span class="icon-bar"></span>
							<span class="icon-bar"></span>
							<span class="icon-bar"></span>
						</button>
						<a class="navbar-brand" href="<?php bloginfo( 'url' ) ?>/" title="<?php bloginfo( 'name' ) ?>" rel="homepage"><?php bloginfo( 'name' ) ?></a>	
					</div>

					<div class="navbar-collapse collapse navbar-responsive-collapse">
						<?php
						$args = array(
							'theme_location' => 'primary',
							'depth'      => 2,
							'container'  => false,
							'menu_class'     => 'nav navbar-nav',
							'walker'     => new Bootstrap_Walker_Nav_Menu()
							);
						if (has_nav_menu('primary')) {
							wp_nav_menu($args);
						}
						?>

					</div>
				</div>
			</div>           
		</nav>