How do I pass an argument to my custom walker?

Question

I've set up a custom walker, and it works as desired when I hard code my variable.

What I want is to be able to call my walker and pass it a variable that is used in the walker.

For example:

 'walker' => new Plus_walker($refine => 'review'),

The walker I've tweaked to output http://URL/review in order to find posts in the review category for this menu item. But I want to be able to use the same walker for 'previews', 'interviews' and more. Thus far my attempts at inputting variables have just broken the whole thing, 'Parse error: syntax error, unexpected T_DOUBLE_ARROW'.

I know I could just rewrite the code and make a few different walkers (Review_walker, Preview_walker etc), but this just seems wrong (and I figure this could be an important thing to know...)

My walker code is here:

class plus_walker extends Walker_Nav_Menu { var $refine; function __construct($refine) { $this->refine = $refine; } function start_el(&$output, $item, $depth, $args) { global $wp_query; $indent = ( $depth ) ? str_repeat( "\t", $depth ) : ''; $class_names = $value = ''; $classes = empty( $item->classes ) ? array() : (array) $item->classes; $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) ); $class_names = ' class="'. esc_attr( $class_names ) . '"'; $output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $value . $class_names .'>'; $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 ) . '' : ''; //This is where I want the argument to live. $modded_url = substr($attributes,0,-1) . '+' . $refine . '"'; $item_output = $args->before; $item_output .= '<a'. $modded_url .'>'; $item_output .= $args->link_before .$prepend.apply_filters( 'the_title', $item->title, $item->ID ).$append; $item_output .= $description.$args->link_after; $item_output .= '</a>'; $item_output .= $args->after; $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args ); } }

And the php call in my templates:

<?php wp_nav_menu( array( 'menu' => 'Handheld', 'container' => 'div', 'container_class' => 'col_1', //'container_id' => , 'menu_class' => 'menu', // 'menu_id' => , 'echo' => true, 'fallback_cb' => 'wp_page_menu', 'items_wrap' => '<ul id="%1$s" class="%2$s">%3$s</ul>', 'depth' => 0, 'walker' => new Plus_walker(array($refine => 'review')), ) ); ?>

I've tried a bunch of different configurations: 'refine' => 'review, with and without the array, but still no joy, just errors (unexpected '=>' mostly).

Rarst · Accepted Answer · 2011-10-16 21:31:19Z

Native walker are triggered with walk() method and are not set up to receive data on creation. You can define custom property and constructor method for this purpose:

class plus_walker extends Walker_Nav_Menu { var $refine; function __construct($refine) { $this->refine = $refine; } } //stuff 'walker' => new plus_walker('review');

After this you can access your custom data as $this->refine in walker's methods.

Hey Rarst.I've tried implementing that, but I keep getting errors. I've updated my code, and included the template call to the walker function. Am I missing something? — josh
– josh, Commented Oct 19, 2011 at 14:27
@josh you can't just use $refine, you need to use $this->refine inside methods. Also you are trying to pass array, note that my example is for single simple variable. — Rarst
– Rarst, Commented Oct 19, 2011 at 14:41

Kevinleary.net · Accepted Answer · 2012-09-26 15:40:04Z

One other way involves adding a custom argument to the wp_nav_menu() function. This is handy if you need to pass a value from outside of the walker class altogether:

wp_nav_menu( array( 'theme_location' => 'secondary', 'depth' => 1, 'walker' => new Custom_Walker(), 'walker_arg' => 'Custom argument value here' ) );

From within the walker class you can then access this custom arg from within start_el() function inside of the walker class (Walker_Nav_Menu::start_el()) like this:

$custom_arg = esc_attr( $args->walker_arg );

Hopefully this helps, it helps with a few obscure scenario's I've come across that Rarst's recommendation above may can't handle well.

Thanks, this is exactly what I needed! I had to change $args->walker_arg to $args['walker_arg'] to get the values to pull through, in case anyone else has the same problem! — louiser89
– louiser89, Commented Mar 2, 2015 at 14:23

Gabriel · Accepted Answer · 2015-09-29 22:34:03Z

You can simply get the custom argument with a slightly altered start_el() function.

First of all, call the element wp_nav_menu (or any other walker using function) with the arguments specified in Kevin Leary's answer.

In the start_el function in your custom walker you can access your data simply via $args['walker_arg']; notice that walker_arg can be altered to fit your needs.

Additionally, with this and partly with Kevin Leary's solution, you can pass more than one custom argument to the walker!

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