解决方法:
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath
{
if (@available(iOS 11.0, *)) {
if ([elementKind isEqualToString:UICollectionElementKindSectionHeader]) {
view.layer.zPosition = 0;
}
}
}
