ios tableview顶部留白

iOS11上废除了automaticallyAdjustsScrollViewInsets

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

iOS11上对滚动视图加入了self-sizeing，默认如果不去实现viewForHeaderInSection就不会调用heightForHeaderInSection
如果不实现上述方法，需要关闭自动估计高度
或者

        self.mainView.estimatedRowHeight = 0;
        self.mainView.estimatedSectionHeaderHeight = 0;
        self.mainView.estimatedSectionFooterHeight = 0;

@https://blog.csdn.net/leonliu070602/article/details/78581278