Top aligned UICollectionViewCells

CollectionViewFlowLayoutSubclass.m

@implementation CollectionViewFlowLayoutSubclass

- (void)awakeFromNib {
	[super awakeFromNib];
}
	
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
	NSArray *attributesToReturn = [super layoutAttributesForElementsInRect:rect];

	for (UICollectionViewLayoutAttributes *attributes in attributesToReturn) {
		if (!attributes.representedElementKind) {
			attributes.frame = [self layoutAttributesForItemAtIndexPath:attributes.indexPath].frame;
		}
	}

	return attributesToReturn;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
	UICollectionViewLayoutAttributes *currentItemAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
	UIEdgeInsets sectionInset = [(UICollectionViewFlowLayout *)self.collectionView.collectionViewLayout sectionInset];

	if (indexPath.item == 0) {
		CGRect frame = currentItemAttributes.frame;
		frame.origin.y = sectionInset.top;
		currentItemAttributes.frame = frame;

		return currentItemAttributes;
	}

	CGRect previousFrame = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:indexPath.item - 1 inSection:indexPath.section]].frame;
	CGRect currentFrame = currentItemAttributes.frame;
	CGRect strecthedCurrentFrame = CGRectMake(currentFrame.origin.x, 0, currentFrame.size.width, self.collectionView.frame.size.height);

	if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) {
		CGRect frame = currentItemAttributes.frame;
		frame.origin.y = frame.origin.y = sectionInset.top;
		currentItemAttributes.frame = frame;

		return currentItemAttributes;
	}

	CGRect frame = currentItemAttributes.frame;
	frame.origin.y = previousFrame.origin.y + previousFrame.size.height + kVerticalSpacing;
	currentItemAttributes.frame = frame;

	return currentItemAttributes;
}

@end