Question

Below is a WordPress function that pulls in a thumbnail image for a menu. How do I add an if/else to display “No thumbail” if there is no thumbail?

I have tried:

$item_output .= apply_filters( 'menu_item_thumbnail' , ( !isset( $args->thumbnail ) && $args->thumbnail ) ) ? 'no thumbnail' : '';

But this had no effect. Sorry if this is a dumb question, but I don’t know PHP.

The function:

class Menu_With_Description extends Walker_Nav_Menu {
    function start_el(&$output, $item, $depth, $args) {
        global $wp_query;


        // get user defined attributes for thumbnail images
        $attr_defaults = array( 'class' => 'nav_thumb' , 'alt' => esc_attr( $item->attr_title ) , 'title' => esc_attr( $item->attr_title ) );
        $attr = isset( $args->thumbnail_attr ) ? $args->thumbnail_attr : '';
        $attr = wp_parse_args( $attr , $attr_defaults );

        $item_output = $args->before;

        // thumbnail image output
        $item_output .= ( isset( $args->thumbnail_link ) && $args->thumbnail_link ) ? '<a' . $attributes . '>' : '';
        $item_output .= apply_filters( 'menu_item_thumbnail' , ( isset( $args->thumbnail ) && $args->thumbnail ) ? get_the_post_thumbnail( $item->object_id , ( isset( $args->thumbnail_size ) ) ? $args->thumbnail_size : 'thumbnail' , $attr ) : '' , $item , $args , $depth );
        $item_output .= ( isset( $args->thumbnail_link ) && $args->thumbnail_link ) ? '</a>' : '';

        // menu link output
        $item_output .= '<a'. $attributes .'>';
        $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
        $item_output .= '</a>';

        // menu description output based on depth
        $item_output .= ( $args->desc_depth >= $depth ) ? '<br /><span class="sub">' . $item->description . '</span>' : '';

        // close menu link anchor
        $item_output .= $args->after;

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

This applies the above to my menu:

add_filter( 'wp_nav_menu_args' , 'my_add_menu_descriptions' );
function my_add_menu_descriptions( $args ) {
    if ( $args['theme_location'] == 'my_menu' ) {
         $args['walker'] = new Menu_With_Description;
         $args['desc_depth'] = 0;
         $args['thumbnail'] = true;
         $args['thumbnail_link'] = true;
         $args['thumbnail_size'] = 'homeboxes';
         $args['thumbnail_attr'] = array( 'class' => 'nav_thumb my_thumb' , 'alt' => 'test' , 'title' => 'test' );
        }
    return $args;   
    }

Answer 1

Don’t modify the Class. Use this filter instead:

add_filter( 'menu_item_thumbnail', 'so_13368049_change_thumb', 10, 4 );

function so_13368049_change_thumb( $thumb, $item , $args , $depth )
{
    if( '' == $thumb )
        return 'No thumbnail';

    return $thumb;
}

And if you were to modify the Class, it should be like this:
('NO THUMBNAIL' instead of '')

    $item_output .= apply_filters( 'menu_item_thumbnail' , ( isset( $args->thumbnail ) && $args->thumbnail ) ? get_the_post_thumbnail( $item->object_id , ( isset( $args->thumbnail_size ) ) ? $args->thumbnail_size : 'thumbnail' , $attr ) : 'NO THUMBNAIL' , $item , $args , $depth );