我在collectionView中遇到scrollToItem(at:at:animated:)方法时遇到问题。滚动到最后一项时，似乎collectionView滚动出视图。当我在那之后尝试向上滚动时，则collectionView位于底部。
NSInteger section = [self numberOfSectionsInCollectionView:collectionView] - 1;
NSInteger item = [self collectionView:collectionView numberOfItemsInSection:section] - 1;
NSIndexPath *lastIndexPath = [NSIndexPath indexPathForItem:item inSection:section];
[collectionView scrollToItemAtIndexPath:lastIndexPath atScrollPosition:UICollectionViewScrollPositionBottom animated:YES];