buddypress.php

function updateUserNicename( $user_id, $posted_field_ids, $errors, $old_values, $new_values ) 
{
	$old_nicename = wp_cache_get( 'bp_user_username_' . $user_id, 'bp' );

    if ( empty( $errors ) ) {
        // update user_nicename
        // field 2 = first name
        // field 3 = last name
        $new_nicename = $new_values[2]['value'] . '-' . $new_values[3]['value'];
        // update user_nicename
        $updated = wp_update_user( array( 'ID' => $user_id, 'user_nicename' => $new_nicename ) );

        if ( is_wp_error( $updated ) ) {
            die($updated);
        } else {
            $new_nicename = get_userdata( $user_id )->user_nicename;
            // wp_cache_delete( 'bp_user_username_' . $user_id, 'bp' );
            // wp_cache_delete( 'bp_core_userdata_' . $user_id, 'bp' );
            wp_cache_replace( 'bp_user_username_' . $user_id, $new_nicename, 'bp' );
        }
	
    }
    $bp = buddypress();
    $bp->displayed_user->domain = str_replace( $old_nicename, $new_nicename, $bp->displayed_user->domain );
}
add_action('xprofile_updated_profile', 'updateUserNicename', 1, 5 );