问根据Wordpress页面中的第一个下拉列表填充第二个下拉列表

EN

function wp_dropdown_pages( $args = '' ) {
$defaults = array(
    'depth' => 0, 'child_of' => 0,
    'selected' => 0, 'echo' => 1,
    'name' => 'page_id', 'id' => '',
    'show_option_none' => '', 'show_option_no_change' => '',
    'option_none_value' => ''
);

$r = wp_parse_args( $args, $defaults );

$pages = get_pages( $r );
$output = '';
// Back-compat with old system where both id and name were based on $name    argument
if ( empty( $r['id'] ) ) {
    $r['id'] = $r['name'];
}

if ( ! empty( $pages ) ) {
    $output = "<select name='" . esc_attr( $r['name'] ) . "' id='" .  esc_attr( $r['id'] ) . "'>\n";
    if ( $r['show_option_no_change'] ) {
        $output .= "\t<option value=\"-1\">" . $r['show_option_no_change'] .  "</option>\n";
    }
    if ( $r['show_option_none'] ) {
        $output .= "\t<option value=\"" . esc_attr( $r['option_none_value']  ) . '">' . $r['show_option_none'] . "</option>\n";
    }
    $output .= walk_page_dropdown_tree( $pages, $r['depth'], $r );
    $output .= "</select>\n";
}

/**
 * Filter the HTML output of a list of pages as a drop down.
 *
 * @since 2.1.0
 *
 * @param string $output HTML output for drop down list of pages.
 */
$html = apply_filters( 'wp_dropdown_pages', $output );

if ( $r['echo'] ) {
    echo $html;
}
return $html;
}