WP Bootstrap Navwalker for BS 2+ and WP 3.6+

<?php

/**
 * Class Name: wp_bootstrap_navwalker
 * GitHub URI: https://github.com/twittem/wp-bootstrap-navwalker
 * Description: A custom WordPress nav walker class to implement the Twitter Bootstrap 2.3.2 navigation style in a custom theme using the WordPress built in menu manager.
 * Version: 1.4.4
 * Author: Edward McIntyre - @twittem
 * License: GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */

class wp_bootstrap_navwalker extends Walker_Nav_Menu {
  
  /**
	 * @see Walker::start_lvl()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param int $depth Depth of page. Used for padding.
	 */
	function start_lvl( &$output, $depth = 0, $args = array() ) {
		$indent = str_repeat("\t", $depth);
		$output .= "\n$indent<ul class=\" dropdown-menu\">\n";
	}

	/**
	 * @see Walker::start_el()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param object $item Menu item data object.
	 * @param int $depth Depth of menu item. Used for padding.
	 * @param int $current_page Menu item ID.
	 * @param object $args
	 */

	function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
		$indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

		/**
		 * Dividers & Headers
	     * ==================
		 * Determine whether the item is a Divider, Header, or regular menu item.
		 * To prevent errors we use the strcasecmp() function to so a comparison
		 * that is not case sensitive. The strcasecmp() function returns a 0 if 
		 * the strings are equal.
		 */
		if (strcasecmp($item->title, 'divider') == 0) {
			// Item is a Divider
			$output .= $indent . '<li class="divider">';
		} else if (strcasecmp($item->title, 'divider-vertical') == 0) {
			// Item is a Vertical Divider
			$output .= $indent . '<li class="divider-vertical">';
		} else if (strcasecmp($item->title, 'nav-header') == 0) {
			// Item is a Header
			$output .= $indent . '<li class="nav-header">' . esc_attr( $item->attr_title );
		} else {

			$class_names = $value = '';

			$classes = empty( $item->classes ) ? array() : (array) $item->classes;
			$classes[] = 'menu-item-' . $item->ID;

			$class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args ) );
			
			//If item has_children add dropdown class to li
			if($args->has_children) {
				$class_names .= ' dropdown';
			}

			$class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';

			$id = apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args );
			$id = $id ? ' id="' . esc_attr( $id ) . '"' : '';

			$output .= $indent . '<li' . $id . $value . $class_names .'>';

			$atts = array();
			$atts['title']  = ! empty( $item->title ) 	   ? $item->title 	   : '';
			$atts['target'] = ! empty( $item->target )     ? $item->target     : '';
			$atts['rel']    = ! empty( $item->xfn )        ? $item->xfn        : '';

			//If item has_children add atts to a
			if($args->has_children) {
				$atts['href']   		= '#';
				$atts['class']			= 'dropdown-toggle';
				$atts['data-toggle']			= 'dropdown';
				$atts['data-target']			= '#';
			} else {
				$atts['href'] = ! empty( $item->url ) ? $item->url : '';
			}

			$atts = apply_filters( 'nav_menu_link_attributes', $atts, $item, $args );

			$attributes = '';
			foreach ( $atts as $attr => $value ) {
				if ( ! empty( $value ) ) {
					$value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
					$attributes .= ' ' . $attr . '="' . $value . '"';
				}
			}

			$item_output = $args->before;
		
			/*
			 * Glyphicons
			 * ===========
			 * Since the the menu item is NOT a Divider or Header we check the see
			 * if there is a value in the attr_title property. If the attr_title
			 * property is NOT null we apply it as the class name for the glyphicon.
			 */

			if(! empty( $item->attr_title )){
				$item_output .= '<a'. $attributes .'><i class="' . esc_attr( $item->attr_title ) . '"></i>&nbsp;';
			} else {
				$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) ? ' <span class="caret"></span></a>' : '</a>';
			$item_output .= $args->after;

			$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
		}
	}

	/**
	 * Traverse elements to create list from elements.
	 *
	 * Display one element if the element doesn't have any children otherwise,
	 * display the element and its children. Will only traverse up to the max
	 * depth and no ignore elements under that depth. 
	 *
	 * This method shouldn't be called directly, use the walk() method instead.
	 *
	 * @see Walker::start_el()
	 * @since 2.5.0
	 *
	 * @param object $element Data object
	 * @param array $children_elements List of elements to continue traversing.
	 * @param int $max_depth Max depth to traverse.
	 * @param int $depth Depth of current element.
	 * @param array $args
	 * @param string $output Passed by reference. Used to append additional content.
	 * @return null Null on failure with no changes to parameters.
	 */

	function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) {
        if ( !$element ) {
            return;
        }

        $id_field = $this->db_fields['id'];

        //display this element
        if ( is_object( $args[0] ) ) {
           $args[0]->has_children = ! empty( $children_elements[$element->$id_field] );
        }

        parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
    }
}

?>