Can someone explain to me how the Walker Class works? Do the methods inside the class always need to overload the parent method?


I searched and read about the walker class. I ran tests, I played around the code and I finally did get to understand it. I hope this can be helpfull to others too.

You'll need to implement the walker class for this.

Here is a simple example.

$defaults = array(
        'theme_location'  => 'primary',
        'container'       => 'ul',
        'menu_class'      => 'nav navbar-nav main-nav',
        'walker'          => new Primary_Walker_Nav_Menu()

wp_nav_menu( $defaults );

In the above block of code, the wp_nav_menu() function takes $defaults as argument. In the array $defaults, the last key is walker. Te walker key's value is object of a class Primary_Walker_Nav_Menu. In functions.php file implement the following code.`

class Primary_Walker_Nav_Menu extends Walker_Nav_Menu {
    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        if ( array_search( 'menu-item-has-children', $item->classes ) ) {
            $output .= sprintf( "\n<li class='dropdown %s'><a href='%s' class=\"dropdown-toggle\" data-toggle=\"dropdown\" >%s</a>\n", ( array_search( 'current-menu-item', $item->classes ) || array_search( 'current-page-parent', $item->classes ) ) ? 'active' : '', $item->url, $item->title );
        } else {
            $output .= sprintf( "\n<li %s><a href='%s'>%s</a>\n", ( array_search( 'current-menu-item', $item->classes) ) ? ' class="active"' : '', $item->url, $item->title );

    function start_lvl( &$output, $depth ) {
        $indent = str_repeat( "\t", $depth );
        $output .= "\n$indent<ul class=\"dropdown-menu\" role=\"menu\">\n";

The start_el() method is used to add the opening HTML tag for a single tree item (such as <li>, <span>, or <a>) to $output.

The start_lvl() method is run when the walker reaches the start of a new "branch" in the tree structure. Generally, this method is used to add the opening tag of a container HTML element (such as <ol>, <ul>, or <div>) to $output.

The output of the above implementation will result in the following html block of code.

<ul id="menu-main-navigation" class="nav navbar-nav main-nav">
   <li class="dropdown ">
      <a href="http://karunshakya.com.np/services/" class="dropdown-toggle">Services</a>
      <ul class="dropdown-menu" role="menu">
         <li><a href="http://karunshakya.com.np/services/selection-et-recrutement/">Sélection et recrutement</a></li>
         <li><a href="http://karunshakya.com.np/services/mise-disposition-de-personnel/">Mise disposition de personnel</a></li>
         <li><a href="http://karunshakya.com.np/services/gestion-de-salaire/">Gestion de salaire</a></li>
   <li><a href="http://karunshakya.com.np/news/">News</a></li>
   <li><a href="http://karunshakya.com.np/medias/">Medias</a></li>
   <li class="last-child"><a href="http://karunshakya.com.np/contactez-nous/">Contactez-nous</a></li>

The link below explains how we can use the walker class http://code.tutsplus.com/tutorials/understanding-the-walker-class--wp-25401

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