设置contentInset时MJRefresh下拉刷新异常

需求:
为了实现tableView和collectionView顶部插入一个tip label，可随着滚动而滑出界面

做法:
(如果collectionView有headerView该多好，但只有tableView才有...)

- (void)addHeaderForCollectionView:(UICollectionView *)collectionView {
    CGFloat headerH = 44;
    collectionView.contentInset = UIEdgeInsetsMake(headerH, 0, 0, 0);
    
    UIView *headerView;
    [collectionView addSubview:({
        UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, -headerH, SCREEN_WIDTH, headerH)];
        view.backgroundColor = [UIColor clearColor];
        headerView = view;
        view;
    })];
    
    UILabel *tipLabel;
    [headerView addSubview:({
        UILabel *label = [[UILabel alloc] init];
        label.font = kFont(10);
        label.textColor = kColor(@"#999999");
        label.numberOfLines = 0;
        label.textAlignment = NSTextAlignmentCenter;
        label.text = @"优质内容将会被小编精选在首页—推荐中曝光哦～\n快去发布优质内容上首页啦";
        tipLabel = label;
        label;
    })];
    [tipLabel mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.centerY.mas_equalTo(0);
    }];
}

bug:
设置了tableView和collectionView的contentInset.top值，发现collectionView下拉刷新时，MJ刷新控件 与 tipLabel展示位置重叠了

solution:
flowLayout.sectionInset.top 或者 flowLayout.headerInset, 均可以.
（CHTCollectionViewWaterfallLayout）

flowLayout.sectionInset = kFeedSecitonInset;// UIEdgeInsetsMake(4, 4, 4, 4);

flowLayout.headerInset = UIEdgeInsetsMake(self.headValue.floatValue, 0, 0, 0);