Filter didn't work on content class (hybrid_post_attributes)

Question

I'm developing my new theme using Hybrid core framework and trying to add my class item on hybrid_post_attributes generated class using filter with this code.

add_filter( 'hybrid_post_attributes', 'my_post_atributes');
function my_post_atributes($attributes){
return  $attributes['class'] = substr_replace($attributes['class'], ' item', -1);
}

I want my 'item' class to be added as the last class from 'hybrid_post_attributes' classes. Here's hybrid_post_attributes function.

function hybrid_post_attributes() {

    $attributes = array();
    $output     = '';

    $attributes['id']    = 'post-' . get_the_ID();
    $attributes['class'] = join( ' ', hybrid_get_post_class() );
    $attributes = apply_atomic( 'post_attributes', $attributes );

    foreach( $attributes as $attr => $value )
        $output .= " {$attr}='{$value}'";

    echo $output;
}

And here's hybrid_get_post_class function.

function hybrid_get_post_class( $class = '', $post_id = null ) {
    static $post_alt;

    $post = get_post( $post_id );

/* Make sure we have a real post first. */
if ( !empty( $post ) ) {

    $post_id = $post->ID;

    /* Add hentry for microformats compliance, the post type, and post status. */
    $classes = array( 'hentry', $post->post_type, $post->post_status );

    /* Post alt class. */
    $classes[] = 'post-' . ++$post_alt;
    $classes[] = ( $post_alt % 2 ) ? 'odd' : 'even alt';

    /* Author class. */
    $classes[] = 'author-' . sanitize_html_class( get_the_author_meta( 'user_nicename' ), get_the_author_meta( 'ID' ) );

    /* Sticky class (only on home/blog page). */
    if ( is_home() && is_sticky() && !is_paged() )
        $classes[] = 'sticky';

    /* Password-protected posts. */
    if ( post_password_required() )
        $classes[] = 'protected';

    /* Has excerpt. */
    if ( post_type_supports( $post->post_type, 'excerpt' ) && has_excerpt() )
        $classes[] = 'has-excerpt';

    /* Has <!--more--> link. */
    if ( !is_singular() && false !== strpos( $post->post_content, '<!--more-->' ) )
        $classes[] = 'has-more-link';

    /* Post format. */
    if ( current_theme_supports( 'post-formats' ) && post_type_supports( $post->post_type, 'post-formats' ) ) {
        $post_format = get_post_format( $post_id );
        $classes[] = ( ( empty( $post_format ) || is_wp_error( $post_format ) ) ? 'format-standard' : "format-{$post_format}" );
    }

    /* Add category and post tag terms as classes. */
    if ( 'post' == $post->post_type ) {

        foreach ( array( 'category', 'post_tag' ) as $tax ) {

            foreach ( (array)get_the_terms( $post->ID, $tax ) as $term ) {
                if ( !empty( $term->slug ) )
                    $classes[] = $tax . '-' . sanitize_html_class( $term->slug, $term->term_id );
            }
}

Did my way of using filter wrong?
Thanks.

Answer 1

For your filter to work, the Hybrid Core code would have to run something like $abcd = apply_filters('hybrid_post_attributes',$something); and I don't see that in the code you posted. In fact, I don't see apply_filters anywhere at all. Based entirely on that posted code, you can't filter those items.

I don't think you understand how filters work. You cannot hook to a function. You need to hook to something specifically created with apply_filters or do_action (for action hooks). See:

Clarification on filters and hooks
http://codex.wordpress.org/Plugin_API

However, my guess, based on the name, is that hybrid_get_post_class is itself hooked to post_class. You should be able to hook your own function to that.

add_filter('post_class', 'my_post_attributes');
function my_post_attributes($classes){
  $classes[] = ' item';
  return $classes;
}

Here is your "one line" version, @ChipBennett.

add_filter('post_class', 'my_post_attributes');
function my_post_attributes($classes){
  return array_merge($classes,array('item'));
}

Answer 2

It looks like your callback is written wrong:

add_filter( 'hybrid_post_attributes', 'my_post_atributes');
function my_post_atributes($attributes){
    return  $attributes['class'] = substr_replace($attributes['class'], ' item', -1);
}

You pass it an array, and you need to return that array. As written, you're only returning one array key. Try modifying the array, then returning it:

add_filter( 'hybrid_post_attributes', 'my_post_atributes');
function my_post_atributes($attributes){
    // Modify
    $attributes['class'] = substr_replace($attributes['class'], ' item', -1);
    // Return
    return $attributes;
}