ios - UICollectionView 添加了多个装饰 View

Question

我正在创建一个基本的 Collection View 布局，它是 UICollectionViewFlowLayout 的子类。但是，我注意到似乎有几个装饰 View 堆叠在一起。

每当用户在上一节中选择一个项目时，我都会使用以下代码添加一个新节。似乎每当我执行这段代码时，装饰 View 的一个额外副本就会添加到每个已经存在的部分。

[collectionView performBatchUpdates:^{
    currentModelArrayIndex++;
    [collectionView insertSections:[NSIndexSet indexSetWithIndex:currentModelArrayIndex]];
    [collectionView reloadSections:[NSIndexSet indexSetWithIndex:currentModelArrayIndex-1]];
} completion:^(BOOL finished) {
    [collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:currentModelArrayIndex] atScrollPosition:UICollectionViewScrollPositionTop animated:YES];
}];

我通过为我的装饰 View 提供 0.2f 的 alpha 并看到它们堆叠起来证实了这一点。

我还执行了 Collection View 层次结构的转储，并看到了 10 个 AFDecorationView 实例，而我应该只看到 4 个:

   | <AFDecorationView: 0x719ee50; baseClass = UICollectionReusableView; frame = (0 65; 768 208.125); alpha = 0; hidden = YES; layer = <CALayer: 0x719eec0>>
   | <AFDecorationView: 0x71ad980; baseClass = UICollectionReusableView; frame = (0 333.125; 768 203.281); alpha = 0; hidden = YES; layer = <CALayer: 0x71adb60>>
   | <AFDecorationView: 0x71afc90; baseClass = UICollectionReusableView; frame = (0 65; 768 208.125); layer = <CALayer: 0x71afd60>>
   | <AFDecorationView: 0xd79ac30; baseClass = UICollectionReusableView; frame = (0 596.406; 768 203.281); alpha = 0; hidden = YES; layer = <CALayer: 0xd79ad00>>
   | <AFDecorationView: 0xd79cf20; baseClass = UICollectionReusableView; frame = (0 333.125; 768 203.281); layer = <CALayer: 0xd79cff0>>
   | <AFDecorationView: 0xd79dac0; baseClass = UICollectionReusableView; frame = (0 65; 768 208.125); layer = <CALayer: 0xd79a980>>
   | <AFDecorationView: 0xd794fd0; baseClass = UICollectionReusableView; frame = (0 859.688; 768 225.938); layer = <CALayer: 0xd7950a0>>
   | <AFDecorationView: 0xd7a1300; baseClass = UICollectionReusableView; frame = (0 596.406; 768 203.281); layer = <CALayer: 0xd7a13d0>></CALayer:>
   | <AFDecorationView: 0xd7a35d0; baseClass = UICollectionReusableView; frame = (0 65; 768 208.125); layer = <CALayer: 0xd794470>>
   | <AFDecorationView: 0xd7a43e0; baseClass = UICollectionReusableView; frame = (0 333.125; 768 203.281); layer = <CALayer: 0xd7a44b0>>

我试过查看 another custom layout example ，但他们似乎也实例化了很多装饰 View 的实例。这可能是 UICollecionView 中的错误吗？还是我们只能在 layoutAttributesForElementsInRect: 每个部分添加一次装饰 View 布局属性？

自定义布局的装饰相关部分如下所示。

@implementation AFCollectionViewFlowLayout

-(id)init
{
    if (!(self = [super init])) return nil;

    [self registerClass:[AFDecorationView class] forDecorationViewOfKind:AFCollectionViewFlowLayoutBackgroundDecoration];

    return self;
}

#pragma mark - Private Helper Methods

-(void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)attributes
{
    //implemented
}

#pragma mark - Overridden Methods

#pragma mark Cell Layout

-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *attributesArray = [super layoutAttributesForElementsInRect:rect];

    NSMutableArray *newAttributesArray = [NSMutableArray array];

    for (UICollectionViewLayoutAttributes *attributes in attributesArray)
    {
        [self applyLayoutAttributes:attributes];

        if (attributes.indexPath.item == 0)
        {
            UICollectionViewLayoutAttributes *newAttributes = [self layoutAttributesForDecorationViewOfKind:AFCollectionViewFlowLayoutBackgroundDecoration atIndexPath:attributes.indexPath];

            [newAttributesArray addObject:newAttributes];
        }
    }

    attributesArray = [attributesArray arrayByAddingObjectsFromArray:newAttributesArray];

    return attributesArray;
}

#pragma mark Decoration View Layout

-(UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString *)decorationViewKind atIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes *layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:decorationViewKind withIndexPath:indexPath];

    if ([decorationViewKind isEqualToString:AFCollectionViewFlowLayoutBackgroundDecoration])
    {
        UICollectionViewLayoutAttributes *tallestCellAttributes;
        NSInteger numberOfCellsInSection = [self.collectionView numberOfItemsInSection:indexPath.section];

        for (NSInteger i = 0; i < numberOfCellsInSection; i++)
        {
            NSIndexPath *cellIndexPath = [NSIndexPath indexPathForItem:i inSection:indexPath.section];

            UICollectionViewLayoutAttributes *cellAttribtes = [self layoutAttributesForItemAtIndexPath:cellIndexPath];

            if (CGRectGetHeight(cellAttribtes.frame) > CGRectGetHeight(tallestCellAttributes.frame))
            {
                tallestCellAttributes = cellAttribtes;
            }
        }

        CGFloat decorationViewHeight = CGRectGetHeight(tallestCellAttributes.frame) + self.headerReferenceSize.height;

        layoutAttributes.size = CGSizeMake([self collectionViewContentSize].width, decorationViewHeight);
        layoutAttributes.center = CGPointMake([self collectionViewContentSize].width / 2.0f, tallestCellAttributes.center.y);
        layoutAttributes.zIndex = -1;
    }

    return layoutAttributes;
}

@end

我每个部分只需要一个装饰 View ，所以我将装饰 View 添加到第一部分。

Answer 1

这似乎是 UICollectionView 中的错误。我已经提交了 bug report与 Apple。