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I am trying to add some ARIA related stuff to the wp_nav_menu function. I use a custom walker class for this purpose:

class Walker_Nav_Menu_With_Aria extends Walker_Nav_Menu { function start_lvl( &$output, $depth = 0, $args = array() ) { $indent = str_repeat("\t", $depth); $output .= "\n$indent<ul class=\"sub-menu\" role=\"group\">\n"; } function end_lvl( &$output, $depth = 0, $args = array() ) { $indent = str_repeat("\t", $depth); $output .= "$indent</ul>\n"; } function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) { $indent = ( $depth ) ? str_repeat( "\t", $depth ) : ''; $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 ) ); $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 ) . '"' : ''; // Add attributes for <li> $li_attributes = ' role="treeitem"'; $li_attributes .= ' aria-expanded="false"'; $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 ) .'"' : ''; // Add attributes for <a> $attributes .= $depth == 0 ? ' tabindex="0"' : ' tabindex="-1"'; $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 .= '</a>'; $item_output .= $args->after; $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args ); } function end_el( &$output, $item, $depth = 0, $args = array() ) { $output .= "</li>\n"; } }

I just copy-pasted the original Walker_Nav_Menu class and added stuff, but I am getting errors because the $args variable treated like an object is really an array. But the really weird thing is that this error persists, even if I pass in the original walker like this:

wp_nav_menu( array( 'theme_location' => 'main-nav', 'walker' => new Walker_Nav_Menu, ) );

These are the error messages I get:

NOTICE: TRYING TO GET PROPERTY OF NON-OBJECT IN /USERS/RUDOLF/SITES/LOCALHOST/WP/WP-INCLUDES/NAV-MENU-TEMPLATE.PHP ON LINE 88 NOTICE: TRYING TO GET PROPERTY OF NON-OBJECT IN /USERS/RUDOLF/SITES/LOCALHOST/WP/WP-INCLUDES/NAV-MENU-TEMPLATE.PHP ON LINE 90 NOTICE: TRYING TO GET PROPERTY OF NON-OBJECT IN /USERS/RUDOLF/SITES/LOCALHOST/WP/WP-INCLUDES/NAV-MENU-TEMPLATE.PHP ON LINE 90 NOTICE: TRYING TO GET PROPERTY OF NON-OBJECT IN /USERS/RUDOLF/SITES/LOCALHOST/WP/WP-INCLUDES/NAV-MENU-TEMPLATE.PHP ON LINE 92

The lines look like this (In the original file!):

(88) $item_output = $args->before; (89) $item_output .= '<a'. $attributes .'>'; (90) $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after; (91) $item_output .= '</a>'; (92) $item_output .= $args->after;
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  • Do you get error if not passing walker at all? Arguments should be object, I think that that is what inline docs say and what wp_nav_menu() passes. Commented Jun 16, 2013 at 15:02
  • No, if I just use the default wp_nav_menu() function without a walker, it works perfectly. Yeah, but why is it an array then? I even var_dump'ed it, no object. Commented Jun 16, 2013 at 15:26
  • I am not sure what is going on then, because passing new Walker_Nav_Menu should behave identically to not passing walker. Is anything else going on, any plugins hooking into / manipulating menu functionality? Commented Jun 16, 2013 at 15:27
  • I just did some additional testing, and I'm sure this is a WordPress bug. In my case, the nav menu I used wasn't assigned in the backend. Therefore the list pages fallback was used, it seems that then the args variable is an array. I will trace this to the source now, then tell you what I found. Commented Jun 16, 2013 at 15:40
  • If I correctly assign a menu, it works! Commented Jun 16, 2013 at 15:40

2 Answers 2

Reset to default
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I get this error when there are no menus defined or no menus set for the location at Appearance->Menus. When that occurs wp_nav_menu uses a page walker fallback.

  1. The fallback (default) for wp_nav_menu is wp_walker_page
  2. which uses wp_page_menu
  3. which uses wp_list_pages
  4. which uses walk_page_tree
  5. which uses Walker_Page not Walker_Nav_Menu.

And apparently the two walkers are not compatible. I don't know why it doesn't fail gracefully. That seems like a bug to me.

With a menu set at wp-admin->Appearance->Menus, your code works.

You can avoid the error by checking to see that there is a menu assigned to the location before trying to use the location.

$locations = get_nav_menu_locations(); if (0 !== $locations['main-nav']) { wp_nav_menu( array( 'theme_location' => 'main-nav', 'walker' => new Walker_Nav_Menu_With_Aria, ) ); }

Or, if you'd prefer less antihistamine addled code ( thanks @Rarst ):

if (has_nav_menu('primary')) { wp_nav_menu( array( 'theme_location' => 'primary', 'walker' => new Walker_Nav_Menu_With_Aria, ) ); }
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  • Fallback is only used when all else fails to display pages. If menu works properly items are walked with walk_nav_menu_tree() which does use Walker_Nav_Menu by default. Commented Jun 16, 2013 at 14:57
  • Nice update! Didn't occur to me wrong function might be grabbing the walker (that's meh). Also there is has_nav_menu() for that check. Commented Jun 16, 2013 at 15:34
  • That is exactly what I just wanted to post :D The nav menu $args are converted to an object in wp-includes/nav-menu-template.php on line 145 by the wp_nav_menu() function. The wp_page_menu() function which is used as a fallback doesn't do that, but instead just passes the array to the Walker from the nav menu which needs the object. If you just add a $args = (object) $args on the top of the start_el function of the Walker class, you can fix this. Where would be the right place to report this to the WordPress team? Commented Jun 16, 2013 at 15:57
  • @Rudolf core bugs should be reported at core.trac.wordpress.org Commented Jun 16, 2013 at 16:00
  • The WP_Post object that is passed as $item is different, too (Because of this, the pages have no names and the list just consists of empty <li> elements). Some serious refactoring would be needed to make these two walkers compatible. Commented Jun 16, 2013 at 16:04
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use below code to repair :

add_filter( 'wp_get_nav_menu_object', 'override_wp_get_nav_menu_object', 10, 2 ); function override_wp_get_nav_menu_object( $menu_obj, $menu ) { if ( ! is_object( $menu_obj ) ) { $menu_obj = (object) array( 'name' => '' ); } return $menu_obj; }
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