Taxonomy dropdown about meta-box HOT 19 CLOSED

$brand_taxonomy = 'modelo';
$taxonomy_name = 'modelo';

add_action('add_meta_boxes', 'my_custom_metabox');
function my_custom_metabox() {
    add_meta_box('custom-taxonomy-dropdown','Brands','taxonomy_dropdowns_box','seminovo','side','high');
}
function taxonomy_dropdowns_box( $post ) {
    global $brand_taxonomy, $taxonomy_name;
    wp_nonce_field('custom-dropdown', 'dropdown-nonce');
    $terms = get_terms( $brand_taxonomy, 'hide_empty=0');
    if ( is_a( $terms, 'WP_Error' ) ) {
        $terms = array();
    }

    $object_terms = wp_get_object_terms( $post->ID, $brand_taxonomy, array('fields'=>'ids'));
    if ( is_a( $object_terms, 'WP_Error' ) ) {
        $object_terms = array();
    }
// you can move the below java script to admin_head
?>
<script type="text/javascript">
    jQuery(document).ready(function() {
    jQuery('#custombrandoptions').change(function() {
    var custombrand = jQuery('#custombrandoptions').val();
    if (custombrand == '0') {
        jQuery('#custommodeloptions').html('');
        jQuery('#modelcontainer').css('display', 'none');
        } else {
        jQuery('#ctd-custom-taxonomy-terms-loading').css('display', 'inline');
        jQuery('#modelcontainer').css('display', 'none');
        var data = {
              'action':'get_brand_models',
              'custombrand':custombrand,
              'dropdown-nonce': jQuery('#dropdown-nonce').val()
              };
        jQuery.post(ajaxurl, data, function(response){
        jQuery('#custommodeloptions').html(response);
        jQuery('#ctd-custom-taxonomy-terms-loading').css('display', 'none');
        jQuery('#modelcontainer').css('display', 'inline');
               });
               }
               });
               });
</script>
<?php
echo "Marca:";
echo "<select id='custombrandoptions' name='custombrands[]'>";
echo "<option value='0'>None</option>";
foreach ($terms as $term ) {
            if ( $term->parent == 0) {
                if ( in_array($term->term_id, $object_terms) ) {
                    $parent_id = $term->term_id;
                    echo "<option value='{$term->term_id}' selected='selected'>{$term->name}</option>";
                  } else {
                    echo "<option value='{$term->term_id}'>{$term->name}</option>";
                }
            }
        }
        echo "</select>";
        echo "<div id='ctd-custom-taxonomy-terms-loading' style='display:none;'>Carregando...</div>";
        echo "<div id='modelcontainer'";
        if ( !isset( $parent_id)) echo " style='display: none;'";
        echo ">";
        echo "Modelo:";
        echo "<select id='custommodeloptions' name='custombrands[]'>";
        if ( isset( $parent_id)) {
            $models = get_terms( $brand_taxonomy, 'hide_empty=0&child_of='.$parent_id);
            foreach ( $models as $model ) {
                 if ( in_array($model->term_id, $object_terms) ) {
                    echo "<option value='{$model->term_id}' selected='selected'>{$model->name}</option>";
                } else {
                    echo "<option value='{$model->term_id}'>{$model->name}</option>";
                }
            }
        }
        echo "</select>";
        echo "</div>";
    }
    add_action('save_post','save_my_custom_taxonomy');
    function save_my_custom_taxonomy( $post_id ) {
        global $brand_taxonomy, $taxonomy_name;
        if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE )
            return;

        if ( !wp_verify_nonce($_POST['dropdown-nonce'], 'custom-dropdown'))
            return;

        $brands = array_map('intval', $_POST['custombrands']);
        wp_set_object_terms($post_id, $brands, $brand_taxonomy);
    }  
    add_action('wp_ajax_get_brand_models', 'get_brand_models');
    function get_brand_models() {
        global $brand_taxonomy, $taxonomy_name;
        check_ajax_referer('custom-dropdown', 'dropdown-nonce');
        if (isset($_POST['custombrand'])) {
            $models = get_terms( $brand_taxonomy, 'hide_empty=0&child_of='. $_POST['custombrand']);
            echo "<option value='0'>Select one</option>";
            foreach ($models as $model) {
                echo "<option value='{$model->term_id}'>{$model->name}</option>";
            }
        }
        die();
    }