Tip: iOS11 collectionView 刷新item上浮问题

if (@available(iOS 11.0, *)) {
        self.collectionView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
        self.collectionView.contentInset = UIEdgeInsetsMake(0,0,0,0);
        self.collectionView.scrollIndicatorInsets = self.collectionView.contentInset;
    }

1、collectionView外部通过获取UICollectionViewFlowLayout，设置其itemSize

self.headerView.collectionView.height = kImgViewH;
 self.headerView.flowLayout.itemSize = CGSizeMake(screenWith,kImgViewH);

2、collectionView通过内部layoutSubviews方法

- (void)layoutSubviews {
    [super layoutSubviews];
    self.layout.itemSize = self.yl_size;
    self.collectionView.frame = self.bounds;
}