将[UICollectionView performBatchUpdates:]与具有UIDynamics的UICollectionViewFlowLayout一起使用

Question

好的基本概述.我有一个UICollectionView我需要支持通过该performBatchUpdates:方法添加和删​​除项目.如果我使用标准UICollectionViewFlowLayout,它工作正常.

但是,当我尝试使用UICollectionViewFlowLayout由a驱动的时UIDynamicAnimator,我一打电话就会崩溃performBatchChanges.

在我的自定义UICollectionViewFlowLayout类中,prepareForCollectionViewUpdates:永远不会调用该方法.UICollectionViewFlowLayout我使用的自定义基于此示例.

崩溃后的控制台输出是......

*** Assertion failure in -[UICollectionViewData layoutAttributesForItemAtIndexPath:], /SourceCache/UIKit/UIKit-2903.23/UICollectionViewData.m:581
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0xc000000000028096> {length = 2, path = 2 - 5}'
*** First throw call stack:
libc++abi.dylib: terminating with uncaught exception of type NSException

有任何想法吗？

Answer 1

尝试

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewLayoutAttributes *layoutAttributes = [self.dynamicAnimator layoutAttributesForCellAtIndexPath:indexPath];
    if(!layoutAttributes) {
        layoutAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
    }
    return layoutAttributes;
}

执行时performBatchUpdates,如果不能看到将由update创建的单元格,则[self.dynamicAnimator layoutAttributesForCellAtIndexPath: 返回nil.所以现在就回来super(或许UICollectionViewFlowLayout)layoutAttributes.当细胞即将展示时,UIDynamicAnimator将为您完成工作.