get_category_children/ the new get_term_children not work

Question

I have a custom Walker for a Advanced Search, that outputs the categories for multiple search by categories in checkbox. The Problem here is, that i use the get_category_children for the children Categories, but its old, and the new code is get_term_children, but when i replace it with it, then comes a error message, like

Warning: substr() expects parameter 1 to be string, object given in /..../search-fields.php on line 269

But the Search Functionality works.

The Code for the Walker Class is:

class Multiple_Walker_Category extends Walker 
{

var $tree_type = 'category';
var $db_fields = array ('parent' => 'parent', 'id' => 'term_id');

function start_lvl(&$output, $depth, $args) {

$indent = str_repeat("\t", $depth);
$output .= "$indent<ul class='children'>\n";

}

function end_lvl(&$output, $depth, $args) {
$indent = str_repeat("\t", $depth);
$output .= "$indent</ul>\n";

}

function start_el($output, $category, $depth, $args)
    {
        extract($args);
        $cat_name =  esc_attr($category->name);

        $cat_name = apply_filters( 'list_cats', $cat_name, $category );
        $cat_children = substr(**get_category_children**( $category->term_id, '', ', '), 0, -2 );

        $output .= "<li><input type='checkbox' onchange='toggle( {$category->term_id}, Array( $cat_children, 999 ) )' class='cb-element'  checked='checked' name='cat_{$category->term_id}' id='cat_{$category->term_id}' />&nbsp;";

        $output .= "<label for='cat_{$category->term_id}'><span></span>$category->name</label>";

}

function end_el(&$output, $category, $depth, $args) {
$output .= "</li>\n";
}
}

How can i replace the old with the new term_children. Thanks everyone for the help.

    function adv_form_cats($args = '')
    {
        $defaults = array(
            'show_option_all' => '',
            'orderby' => 'name',
            'order' => 'ASC', 
                        'show_last_update' => 0,
            'style' => 'list', 
                        'show_count' => 0,
            'hide_empty' => 1, 
                        'use_desc_for_title' => 1,
            'child_of' => 0, 
                        'feed' => '',
            'feed_image' => '', 
                         'exclude' => '',
            'hierarchical' => true, 
                        'title_li' => '',
            'echo' => 0
        );

        $r = wp_parse_args( $args, $defaults );

        if ( !isset( $r['pad_counts'] ) && $r['show_count'] && $r['hierarchical'] ) {
            $r['pad_counts'] = true;
        }

        if ( isset( $r['show_date'] ) ) {
            $r['include_last_update_time'] = $r['show_date'];
        }

        extract( $r );

        $categories = get_categories($r);

        $output = '';
        if ( $title_li && 'list' == $style )
                $output = '<li class="categories">' . $r['title_li'] . '<ul>';

        if ( empty($categories) ) {
            if ( 'list' == $style )
                $output .= '<li>' . __("No categories","WPL") . '</li>';
            else
                $output .= __("No categories","WPL");
        } else {
            global $wp_query;

            if( !empty($show_option_all) )
                if ('list' == $style )

        $output .= "<li><input type='checkbox' id='checkAll' checked='checked' name='checkall'  />&nbsp;";

        $output .= "<label for='checkall'><span></span>".__('Check All', 'WPL').'</label>';

            if ( is_category() )
                $r['current_category'] = $wp_query->get_queried_object_id();

            if ( $hierarchical )
                $depth = 0;  // Walk the full depth.
            else
                $depth = -1; // Flat.

            $output .= walk_category_new_tree($categories, $depth, $r);
        }

        if ( $title_li && 'list' == $style )
            $output .= '</ul></li>';

        $output = apply_filters('wp_list_categories', $output);




    return $output;
    }


function walk_category_new_tree()
    {
        $walker = new Multiple_Walker_Category;
        $args = func_get_args();
        return call_user_func_array(array(&$walker, 'walk'), $args);
    }

Answer 1

get_term_children returns an array or an object (WP_Error) and you are treating it like a string when you try to feed it to substr. I am not sure what you are trying to do with that line of code but in general you need to check that you are dealing with an array and not an error and process accordingly.

$cat_children = get_category_children( $category->term_id, '', ', ');
if (is_wp_error($cat_children)) {
  // do stuff
} elseif (is_array($cat_children)) {
  // do other stuff
  // I don't really know what you want to do here. 
  // Your code would, if I am reading right, chop two characters off of a string
  // which strikes me as a odd thing to do given the data you dealing with
}

http://php.net/manual/en/function.substr.php

http://codex.wordpress.org/Function_Reference/is_wp_error

http://php.net/manual/en/function.is-array.php