janfeng on "About add custom fields to bbpress topic"

I want add custom fields to bbpress topic :

add_action ( 'bbp_theme_before_topic_form_content', 'bbp_extra_fields');
function bbp_extra_fields() {
   $value = get_post_meta( bbp_get_topic_id(), 'bbp_extra_field1', true);
   echo '<label for="bbp_extra_field1">Extra Field 1</label><br>';
   echo "<input type='text' name='bbp_extra_field1' value='".$value."'>";
}

add_action ( 'bbp_new_topic', 'bbp_save_extra_fields', 10, 1 );
add_action ( 'bbp_edit_topic', 'bbp_save_extra_fields', 10, 1 );

function bbp_save_extra_fields($topic_id=0) {
  if (isset($_POST) && $_POST['bbp_extra_field1']!='')
    update_post_meta( $topic_id, 'bbp_extra_field1', $_POST['bbp_extra_field1'] );
}

How to use this fields ?

If want to always display behind topics title, How ?!

For example :

Loop-topics
Post title
The browser title
……..