这里有两个问题，一个是性能问题，另一个是大问题，如果启用调试，将返回一堆错误

这里的性能问题是您第一次获得条款。看来你在这里的目标是只获得顶级条款，而你却获得了所有条款。我想补充一下\'parent\' => 0 只获取顶级术语的参数。然后，您可以在检查的地方删除条件if ( $term->parent == 0 ) 因为所有条款都是顶级条款0 作为术语父级，因此此条件将始终返回true

你的大问题是这个代码，我不理解你的逻辑

    $uchildren =get_terms( $taxonomy, array(\'hide_empty\' => 0, \'parent\' => $term->term_id ));

    $children = array();
    foreach ($uchildren as $child) {
        $cterm = get_term_by( \'id\', $child, $taxonomy );
        // If include array set, exclude unless in array.
        if ( is_array( $include ) && ! in_array( $cterm->slug, $include ) ) continue;
        $children[$cterm->name] = $cterm;
    }
    ksort($children);

为什么要使用get_term_by() 在这里$child 已保存您使用的术语属性get_terms() 检索术语。

你不仅仅是在使用get_term_by() 这里是错误的，但您的参数是无效的，并且您正在向它传递一个完整的对象。您应该咨询法典以正确使用此功能。总之，应该从代码中删除该部分

那部分应该是这样的

    $uchildren =get_terms( $taxonomy, array(\'hide_empty\' => 0, \'parent\' => $term->term_id ));

    $children = array();
    foreach ($uchildren as $child) {
        if ( is_array( $include ) && ! in_array( $child->slug, $include ) ) continue;
        $children[$child->name] = $child;
    }
    ksort($children);

function my_dropdown_categories( $taxonomy, $current_selected = \'\', $include = null ) 
{
    /*
     * Declare your variable first. Without this, your code has a bug if no terms are found
     */
    $list_of_terms = \'\';

    /**
    * Get all parent terms. Note we use \'parent\' => 0 to only get top level terms
    *
    * @see get_terms
    * @link http://codex.wordpress.org/Function_Reference/get_terms
    */
    $terms = get_terms( $taxonomy, array( \'orderby\' => \'name\', \'parent\' => 0 ) );

    /*
    * Use curlies here to enclose your statement. Also, check whether or not you have terms
    */
    if ( $terms && ! is_wp_error( $terms ) ) {

        /*
        * Moved this section inside your if statement. We don\'t want to display anything on empty terms
        */
        $list_of_terms .= \'<select id="location" class="selectboxSingle" name="location">\';

        foreach ( $terms as $term ) {

            // If include array set, exclude unless in array.
            if ( is_array( $include ) && ! in_array( $term->slug, $include ) ) continue;

            $select = ($current_selected == $term->slug) ? "selected" : ""; // Note: ==

            /*
             * Use the parent term term id as parent to get direct children of the term
             * Use child_of if you need to get all descendants of a term
             */
            $uchildren = get_terms( $taxonomy, array(\'hide_empty\' => 0, \'parent\' => $term->term_id ));

            $children = array();
            foreach ($uchildren as $child) {
                // If include array set, exclude unless in array.
                if ( is_array( $include ) && ! in_array( $child->slug, $include ) ) continue;
                $children[$child->name] = $child;
            }
            ksort($children);

            // PARENT TERM      
            if ($term->count > 0) {
                $list_of_terms .= \'<option class ="group-result" value="\'.$term->slug.\'" \'.$select.\'>\' . $term->name .\' </option>\';
            } else {
                $list_of_terms .= \'<option value="\'.$term->slug.\'" \'.$select.\'>\'. $term->name .\' </option>\';
            };

            // now the CHILDREN.
            foreach($children as $child) {
                $select = ($current_selected == $child->slug) ? "selected" : ""; // Note: child, not cterm
                $list_of_terms .= \'<option class="result-sub" value="\'.$child->slug.\'" \'.$select.\'>\'. $child->name.\' </option>\';
            } //end foreach

        }

        /*
        * Moved this section inside your if statement. We don\'t want to display anything on empty terms
        */
        $list_of_terms .= \'</select>\';

    }
    return $list_of_terms;
}