按层级输出自定义分类法的所有分类

总结
本篇教程共写了两段代码，如果你并不清楚如何应用，请往下看。

首先，将本教程用到的一个函数放在主题的functions.php文件中，如下。

/**
*获取任意分类的"顶级父分类",返回分类ID,若本身是顶级分类,返回本身ID
* $term_id 分类的ID
* $taxonomy 分类法，默认为category
* $top_level 人为设定的顶级分类的父分类，默认为0。范例，若设置为3，则将ID为3的分类的第一级子分类定义"顶级父分类"
**/
function ashuwp_get_top_term_id ($term_id ,$taxonomy='category', $top_level=0) {
    while ($term_id != $top_level) {
        $term = get_term($term_id, $taxonomy);
        $term_id = $term->parent;
        $parent_id = $term->term_id;
    }
    return $parent_id;
}

再将下面一整段代码放在要输出分类列表的地方。

<?php
//分类页面
if(is_tax('products')){
  $currentterm = get_queried_object(); //获取当前分类
  $currentterm_id = $currentterm->term_id;
  //当前分类的顶级父分类ID
  $top_term_id = ashuwp_get_top_term_id($currentterm->term_id,'products');
  //获取顶级分类对象
  $top_term = get_term($top_term_id,'products');
  //当前分类ID、当前分类的父分类ID都是当前访问，放入$current_array数组
  $current_array = array($currentterm_id);
  $parent_id = $currentterm->parent;
  while($parent_id){
    $current_array[] = $parent_id;
    $parent_term = get_term($parent_id, 'products');
    $parent_id = $parent_term->parent;
  }
}elseif(is_singular('product')){
  //单页面
  /*获取文章所属分类，文章同属多个分类，将第一个分类当做“当前分类”
  *重复上面工作，将当前分类ID、当前分类的父分类ID都是当前访问，放入$current_array数组
  */
  $terms = get_the_terms( $post->ID, 'products' );
  if ( $terms && ! is_wp_error( $terms ) ) :
    $currentterm = current($terms);
    $current_array[] = $currentterm->term_id;
    $top_term_id = ashuwp_get_top_term_id($currentterm->term_id,'products');
    $top_term = get_term($top_term_id,'products');
    $parent_id = $currentterm->parent;
    while($parent_id){
      $current_array[] = $parent_id;
      $parent_term = get_term($parent_id, 'products');
      $parent_id = $parent_term->parent;
    }
  else:
    $currentterm_id = 0;
    $top_term_id = 0;
    $current_array = array();
  endif;
}else{
  //若为归档页面，则没有当前访问
  $currentterm_id = 0;
  $top_term_id = 0;
  $current_array = array();
}
//先获取所有顶级分类
$top_args = array(
  'taxonomy'=>'products', //分类法名称
  'hide_empty'=>false,
  'parent'=>0, //顶级分类的父级都是0
);
$top_terms = get_terms($top_args);
if ( $top_terms && ! is_wp_error( $top_terms ) ) :
  echo '<ul class="top_ul">'; //最外层ul标签
  //顶级分类循环输出
  foreach( $top_terms as $top_term ):
    $current = '';
    //若这个顶级分类的ID在数组$current_array中，为当前访问项
    if(in_array($top_term->term_id,$current_array))
      $current = 'class="current"';
  ?>
    <li <?php echo $current; ?>>
      <a href="<?php echo get_term_link($top_term,'products'); ?>"><?php echo $top_term->name; ?></a>
      <?php
      //获取当前顶级分类的子分类
      $child_args = array(
        'taxonomy'=>'products',
        'hide_empty'=>false,
        'parent'=>$top_term->term_id,
      );
      $child_terms = get_terms($child_args);
      if ( $child_terms && ! is_wp_error( $child_terms ) ) :
        echo '<ul>'; //第二层ul标签
        //循环子分类
        foreach($child_terms as $child_term):
          $current = '';
          //若这个子分类的ID在数组$current_array中，为当前访问项
          if(in_array($child_term->term_id,$current_array))
            $current = 'class="current"';
          ?>
            <li <?php echo $current; ?>><a href="<?php echo get_term_link($child_term,'products'); ?>"><?php echo $child_term->name; ?></a></li>
          <?php
          endforeach;
        echo '</ul>';
      endif;
      ?>
    </li>
  <?php
  endforeach;
  echo '</ul>';
endif;
?>