上滑隐藏导航栏下拉显示导航栏效果

下拉的效果

上拉的效果 就是这么简单就OK啦！ - (void)scrollViewDidScroll:(UIScrollView *)scrollView {         CGFloat thresholdDistance = 100;         CGFloat percent = scrollView.contentOffset.y/thresholdDistance;         percent = MAX(0, MIN(1, percent));         [self.specialDetailsHeaderView doctorNavigationHiddenBackBtn:percent];         [self.navigationView setAlpha:percent];      }