@Override
  public ActionCallback selectNextContent() {
    int contentCount = getContentCount();
    LOG.assertTrue(contentCount > 1);
    Content selectedContent = getSelectedContent();
    int index = selectedContent == null ? -1 : getIndexOfContent(selectedContent);
    index = (index + 1) % contentCount;
    final Content content = getContent(index);
    if (content == null) {
      return null;
    }
    return setSelectedContentCB(content, true);
  }
@Override
  public ActionCallback selectNextContent()