UICollectionView performBatchUpdates:为所有部分设置动画 [英] UICollectionView performBatchUpdates: animates all sections

问题描述

我正在编写自定义 UICollectionViewFlowLayout 并且我注意到所有部分都会调用 initialLayoutAttributesForAppearingItemAtIndexPath: 和 initialLayoutAttributesForAppearingDecorationElementOfKind:atIndexPath:当我在集合视图上调用 performBatchUpdates:completion: 时.结果是 所有 部分都应用了动画，而不是 只是 新添加的部分.

I'm writing a custom UICollectionViewFlowLayout and I've noticed that initialLayoutAttributesForAppearingItemAtIndexPath: and initialLayoutAttributesForAppearingDecorationElementOfKind:atIndexPath: will be called for all sections when I invoke performBatchUpdates:completion: on the collection view. The result is that all sections have the animation applied to them instead of just the newly added section.

[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];
}];

到目前为止，我尝试的是删除对 performBatchUpdates:completion: 的调用以代替简单的更新，但无论如何，已经存在的部分(所有部分)都是动画的.我想出了一个检查解决方案，以确保我正在更改 only 最后一部分的布局属性，但感觉很hacky.

What I've tried so far is removing the call to performBatchUpdates:completion: in lieu of simple updates, but the already existing sections (all of them) are animated in anyway. I've come up with a solution of checking to make sure that I'm changing the layout attributes of only the last section, but it feels hacky.

if (decorationIndexPath.section == [(id<UICollectionViewDataSource>)self.collectionView.delegate numberOfSectionsInCollectionView:self.collectionView] - 1)
{
   layoutAttributes.alpha = 0.0f;
   layoutAttributes.transform3D = CATransform3DMakeTranslation(-CGRectGetWidth(layoutAttributes.frame), 0, 0);
}

这是只为某些部分设置动画的正确方法吗?

Is this the proper way to go about animating only some sections?

推荐答案

好的，我有答案了；它并没有比前一个漂亮很多，但它使布局不会接触数据源，所以它更干净.

OK, I've got an answer; it's not a lot prettier than the previous one, but it keeps the layout from touching the datasource, so it's cleaner.

基本上，我们需要重写 prepareForCollectionViewUpdates: 和 finalizeCollectionViewUpdates 以跟踪我们正在插入的部分.我有一个可变集，其中包含我们要插入的部分的 NSNumber 实例.

Basically, we need to override prepareForCollectionViewUpdates: and finalizeCollectionViewUpdates to keep track of the sections that we're inserting. I have a mutable set that contains NSNumber instances of the sections that we're inserting.

-(void)prepareForCollectionViewUpdates:(NSArray *)updateItems
{
    [super prepareForCollectionViewUpdates:updateItems];

    [updateItems enumerateObjectsUsingBlock:^(UICollectionViewUpdateItem *updateItem, NSUInteger idx, BOOL *stop) {
        if (updateItem.updateAction == UICollectionUpdateActionInsert)
        {
            [insertedSectionSet addObject:@(updateItem.indexPathAfterUpdate.section)];
        }
    }];
}

-(void)finalizeCollectionViewUpdates
{
    [super finalizeCollectionViewUpdates];

    [insertedSectionSet removeAllObjects];
}

接下来，在设置项目和装饰视图的初始布局属性时，我会检查索引路径的部分是否包含在该集合中.

Next, I check to see if the index path's section is included in that set when setting the initial layout attributes for items and decoration views.

-(UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingDecorationElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)decorationIndexPath
{
    UICollectionViewLayoutAttributes *layoutAttributes;

    if ([elementKind isEqualToString:AFCollectionViewFlowLayoutBackgroundDecoration])
    {
        if ([insertedSectionSet containsObject:@(decorationIndexPath.section)])
        {
            layoutAttributes = [self layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:decorationIndexPath];
            layoutAttributes.alpha = 0.0f;
            layoutAttributes.transform3D = CATransform3DMakeTranslation(-CGRectGetWidth(layoutAttributes.frame), 0, 0);
        }
    }

    return layoutAttributes;
}

-(UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
    UICollectionViewLayoutAttributes *layoutAttributes;

    if ([insertedSectionSet containsObject:@(itemIndexPath.section)])
    {
        layoutAttributes = [self layoutAttributesForItemAtIndexPath:itemIndexPath];
        layoutAttributes.transform3D = CATransform3DMakeTranslation([self collectionViewContentSize].width, 0, 0);
    }

    return layoutAttributes;
}

否则我会从这些方法返回 nil，因为 nil 是默认值.

I'm returning nil from these methods otherwise because nil is the default value.

这还具有更好的旋转动画的额外好处.

This has the added benefit of having nicer rotation animations, as well.

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