我想用wp_list_categories 为了帮助我操作列表类，我希望在start_lvl 方法，所以我尝试使用$category->term_id 但是抛出了错误。现在我只想在start_lvl 方法来匹配我在start_el 输出，请在下面的类中检查此行

$output .= "<span id=\\"$category->term_id\\" class=\\"toggle\\" onClick=\\"toggleMe(this.id);\\" style=\\"cursor:pointer\\">&#9660</span>";

            <?php
        //error_reporting(E_ALL);
        /*
        Plugin Name: YB Walker Categories List
        Plugin URI: https://prosentra.com
        Description: Displays a list of categories using  walker class
        Version: 1.0.0
        Author: Mohammad Omar
        Author URI: https://prosentra.com
        Text Domain: yb-walker-categories-list
        License: GPL2
        */

        if ( ! class_exists( \'YB_Cats_Walk\' ) ) {
            class YB_Cats_Walk extends Walker_Category{
        public $tree_type = \'genre\';
                /**
                 * Start Level.
                 *
                 * @see Walker::start_lvl()
                 * @since 3.0.0
                 *
                 * @access public
                 * @param mixed $output Passed by reference. Used to append additional content.
                 * @param int   $depth (default: 0) Depth of page. Used for padding.
                 * @param array $args (default: array()) Arguments.
                 * @return void
                 */

                public function start_lvl( &$output, $depth = 0, $args = array() ) {
                    $indent = str_repeat( "\\t", $depth );
                    $output .= "\\n$indent<ul id = \\"dropdown-$category->term_id\\" style=\\"display: none;\\">\\n";
                }

                public function end_lvl( &$output, $depth = 0, $args = array() ) {
                    $indent = str_repeat("\\t", $depth);
                    $output .= "$indent</ul>\\n";
                }

                public function start_el(  &$output, $category, $depth = 0, $args = array(), $id = 0 ) {
                            /** This filter is documented in wp-includes/category-template.php */
                $cat_name = apply_filters(
                    \'list_cats\',
                    esc_attr( $category->name ),
                    $category
                );

                // Don\'t generate an element if the category name is empty.
                if ( ! $cat_name ) {
                    return;
                }

                $link = \'<a href="\' . esc_url( get_term_link( $category ) ) . \'" \';
                if ( $args[\'use_desc_for_title\'] && ! empty( $category->description ) ) {
                    /**
                     * Filters the category description for display.
                     *
                     * @since 1.2.0
                     *
                     * @param string $description Category description.
                     * @param object $category    Category object.
                     */
                    $link .= \'title="\' . esc_attr( strip_tags( apply_filters( \'category_description\', $category->description, $category ) ) ) . \'"\';
                }

                $link .= \'>\';
                $link .= $cat_name . \'</a>\';

                if ( ! empty( $args[\'feed_image\'] ) || ! empty( $args[\'feed\'] ) ) {
                    $link .= \' \';

                    if ( empty( $args[\'feed_image\'] ) ) {
                        $link .= \'(\';
                    }

                    $link .= \'<a href="\' . esc_url( get_term_feed_link( $category->term_id, $category->taxonomy, $args[\'feed_type\'] ) ) . \'"\';

                    if ( empty( $args[\'feed\'] ) ) {
                        $alt = \' alt="\' . sprintf(__( \'Feed for all posts filed under %s\' ), $cat_name ) . \'"\';
                    } else {
                        $alt = \' alt="\' . $args[\'feed\'] . \'"\';
                        $name = $args[\'feed\'];
                        $link .= empty( $args[\'title\'] ) ? \'\' : $args[\'title\'];
                    }

                    $link .= \'>\';

                    if ( empty( $args[\'feed_image\'] ) ) {
                        $link .= $name;
                    } else {
                        $link .= "<img src=\'" . $args[\'feed_image\'] . "\'$alt" . \' />\';
                    }
                    $link .= \'</a>\';

                    if ( empty( $args[\'feed_image\'] ) ) {
                        $link .= \')\';
                    }
                }

                if ( ! empty( $args[\'show_count\'] ) ) {
                    $link .= \' (\' . number_format_i18n( $category->count ) . \')\';
                }
                if ( \'list\' == $args[\'style\'] ) {
                    $output .= "\\t<li";
                    if($this->has_children){

                        $css_classes = array(
                        \'has-children\',
                        \'cat-item\',
                        \'cat-item-\' . $category->term_id, 
                    );
                    }
                    $css_classes = array(
                    \'has-children\',
                        \'cat-item\',
                        \'cat-item-\' . $category->term_id,  
                    );


                    if ( ! empty( $args[\'current_category\'] ) ) {
                        // \'current_category\' can be an array, so we use `get_terms()`.
                        $_current_terms = get_terms( $category->taxonomy, array(
                            \'include\' => $args[\'current_category\'],
                            \'hide_empty\' => false,
                        ) );

                        foreach ( $_current_terms as $_current_term ) {
                            if ( $category->term_id == $_current_term->term_id ) {
                                $css_classes[] = \'current-cat\';
                            } elseif ( $category->term_id == $_current_term->parent ) {
                                $css_classes[] = \'current-cat-parent\';
                            }
                            while ( $_current_term->parent ) {
                                if ( $category->term_id == $_current_term->parent ) {
                                    $css_classes[] =  \'current-cat-ancestor\';
                                    break;
                                }
                                $_current_term = get_term( $_current_term->parent, $category->taxonomy );
                            }
                        }
                    }

                    /**
                     * Filters the list of CSS classes to include with each category in the list.
                     *
                     * @since 4.2.0
                     *
                     * @see wp_list_categories()
                     *
                     * @param array  $css_classes An array of CSS classes to be applied to each list item.
                     * @param object $category    Category data object.
                     * @param int    $depth       Depth of page, used for padding.
                     * @param array  $args        An array of wp_list_categories() arguments.
                     */
                    $css_classes = implode( \' \', apply_filters( \'category_css_class\', $css_classes, $category, $depth, $args ) );

                    $output .=  \' class="\' . $css_classes . \'"\';
                    $output .= ">$link\\n";
                    if($this->has_children){
                    $output .= "<span id=\\"$category->term_id\\" class=\\"toggle\\" onClick=\\"toggleMe(this.id);\\" style=\\"cursor:pointer\\">&#9660</span>";
                 }
                } elseif ( isset( $args[\'separator\'] ) ) {
                    $output .= "\\t$link" . $args[\'separator\'] . "\\n";
                } else {
                    $output .= "\\t$link<br />\\n";
                }

                }
                public function end_el( &$output, $page, $depth = 0, $args = array() ) {

                        $output .= "</li>\\n";
                }

                }

            }