iOS11下，凡是隱藏了導(dǎo)航欄的界面，具有ScrollView的子類的界面，都會(huì)在滑動(dòng)或者pop后發(fā)生下沉。解決方法：

if (@available(iOS 11.0, *)) {
        self.scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    } else {
        self.automaticallyAdjustsScrollViewInsets = NO;
    }