/**
  * change taxonomy event
  */
 public function _hw_change_terms_taxonomy()
 {
     if (!wp_verify_nonce($_REQUEST['nonce'], "hw_change_terms_taxonomy_nonce")) {
         exit("No naughty business please");
     }
     if (!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
         $out = hw_get_terms_list($_REQUEST['tax'], false, array('name' => hwtpl_mc_decrypt($_REQUEST['name'], self::ENCRYPTION_KEY), 'id' => hwtpl_mc_decrypt($_REQUEST['id'], self::ENCRYPTION_KEY)));
         $result['html'] = isset($out) ? $out : '';
         $result = json_encode($result);
         echo $result;
     } else {
         header("Location: " . $_SERVER["HTTP_REFERER"]);
     }
     die;
 }
        <p>
            <label>
                <?php 
_e('Term');
?>
:
            </label>
        <div id="holder-<?php 
echo $this->get_field_id("cat_");
?>
">
            <?php 
if (isset($instance['tax']) && $instance['tax']) {
    ?>
                <?php 
    echo hw_get_terms_list($instance['tax'], isset($instance["cat_"]) && $instance["cat_"] ? $instance['cat_'] : '', array('name' => $this->get_field_name('cat_'), 'id' => $this->get_field_id('cat_')));
    ?>
            <?php 
} else {
    echo __('Chọn Taxonomy.');
}
?>
            <?php 
//wp_dropdown_categories( array( 'name' => $this->get_field_name("cat_"),'show_option_all' => 'All','hide_empty' => 0, 'selected' => $instance["cat"] ) );
?>
        </div>
        </p>
        <p>
            <label for="<?php 
echo $this->get_field_id('author');
?>