Ios UICollectionView页眉和页脚的行为非常奇怪

我正在UIViewController中使用基类UICollectionViewFlowLayout实现基类UICollectionView。我的控制器是集合视图委托和数据源。只有项目视图和补充视图是自定义类，没有NIB。据我所知，一切都是标准实现。我尽可能地把它保留下来

HeaderView是UICollectionReusableView的一个子类

这是我的收藏视图创建

-(void) viewDidLoad {

    [super viewDidLoad];

    UICollectionViewFlowLayout *flow = [[UICollectionViewFlowLayout alloc] init];
    flow.headerReferenceSize = CGSizeMake(0, 50);
    flow.footerReferenceSize = CGSizeMake(0, 50);
    flow.itemSize = CGSizeMake(100, 150);
    flow.sectionInset = UIEdgeInsetsMake(20, 20, 20, 20);
    [flow setScrollDirection:UICollectionViewScrollDirectionVertical];

    cellID = @"CollectionCellIdentifier";
    headerID = @"header";
    footerID = @"footer";


    collection = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 70, self.view.frame.size.width, self.view.frame.size.height-70) collectionViewLayout:flow];

    [collection registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:cellID];
    [collection registerClass:[HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerID];
    [collection registerClass:[HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerID];
    [collection setDelegate:self];
    [collection setDataSource:self];

    [self.view addSubview:collection];

}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{

    HeaderView *header;

    NSString *suppID = headerID;

    if ([kind isEqualToString:UICollectionElementKindSectionFooter]) {
         suppID = footerID;
    }

    header = (HeaderView *)[collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:suppID forIndexPath:indexPath];

    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        if (indexPath.section == kInSection) {
            header.label.text = @"In Groups";
        }
        else {
            header.label.text = @"Other Groups";
        }
    }
    else {
        header.label.text = @"";
    }


    return header;

}

下面是我的补充视图创建

-(void) viewDidLoad {

    [super viewDidLoad];

    UICollectionViewFlowLayout *flow = [[UICollectionViewFlowLayout alloc] init];
    flow.headerReferenceSize = CGSizeMake(0, 50);
    flow.footerReferenceSize = CGSizeMake(0, 50);
    flow.itemSize = CGSizeMake(100, 150);
    flow.sectionInset = UIEdgeInsetsMake(20, 20, 20, 20);
    [flow setScrollDirection:UICollectionViewScrollDirectionVertical];

    cellID = @"CollectionCellIdentifier";
    headerID = @"header";
    footerID = @"footer";


    collection = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 70, self.view.frame.size.width, self.view.frame.size.height-70) collectionViewLayout:flow];

    [collection registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:cellID];
    [collection registerClass:[HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerID];
    [collection registerClass:[HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerID];
    [collection setDelegate:self];
    [collection setDataSource:self];

    [self.view addSubview:collection];

}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{

    HeaderView *header;

    NSString *suppID = headerID;

    if ([kind isEqualToString:UICollectionElementKindSectionFooter]) {
         suppID = footerID;
    }

    header = (HeaderView *)[collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:suppID forIndexPath:indexPath];

    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        if (indexPath.section == kInSection) {
            header.label.text = @"In Groups";
        }
        else {
            header.label.text = @"Other Groups";
        }
    }
    else {
        header.label.text = @"";
    }


    return header;

}

当我运行此操作时，项目看起来很好。第一节的标题（kInSection）显示良好。第一节底部没有页脚。第二节（kOutSection）顶部没有标题。这些页脚和页眉在第二节下面。第二节标题显示的文本正确无误

最奇怪的是，当我将集合视图向上滚动足够远时，我可以看到第二部分下方的页眉和页脚。。。当我滚动经过它们应该渲染的位置时，它们会从屏幕中间消失。这真的很奇怪

否则，此集合视图工作正常。我可以与项目交互，我可以插入和删除项目，等等

UICollectionView是否不可靠？我真的做错什么了吗？以前有人经历过类似的事情吗？在我通常可靠的iOS开发研究中，我没有发现任何东西

如果有人需要任何其他信息，请告诉我。但实际上，这是我在研究中收集到的基本实现