[WordPress]管理画面の投稿一覧にタクソノミー絞り込み機能追加

functions.php

function add_post_restrict_taxonomy() {
  global $post_type;
  if ( 'post' == $post_type ) {
  ?>
    <select name="item_category">
      <option value="">タクソノミー一覧</option>
      <?php
      $terms = get_terms('item_category');
      foreach ($terms as $term) { ?>
        <option value="<?php echo $term->slug; ?>"><?php echo $term->name; ?></option>
      <?php } ?>
    </select>
  <?php
  }
}
add_action( 'restrict_manage_posts', 'add_post_restrict_taxonomy' );