#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
  if (scrollView == _tableView) {
    DDLogVerbose(@"%f", scrollView.contentOffset.y);
    if (_tableView.contentOffset.y >= _backgroundScrollView.height / 3.0 * 1.0) {
      [UIView animateWithDuration:0.5 animations:^{
        _tableView.frame = CGRectMake(0, self.originY + 40, kScreenWidth, kScreenHeight - 64);
        _backgroundScrollView.frame = CGRectMake(0, self.originY - _backgroundScrollView.height + 40,
                                                 kScreenWidth, _backgroundScrollView.height);
      }];
    } else if (_tableView.contentOffset.y <= -44 && _backgroundScrollView.originY < self.originY) {
      [UIView animateWithDuration:0.5 animations:^{
        _backgroundScrollView.frame = CGRectMake(0, self.originY,
                                                 kScreenWidth,
                                                 _backgroundScrollView.height);
                _tableView.frame = CGRectMake(0, _backgroundScrollView.bottomY,
                                              kScreenWidth,
                                              kScreenHeight - 64 - _backgroundScrollView.height);
      }];
    }
  }
}

效果如下，超过一定范围会自动显示与隐藏