How can I change the scroll direction in UICollectionView?

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];

Note too that it seems to be fine to call this in prepareForLayout in your flow layout…

@interface LayoutHorizontalThings : UICollectionViewFlowLayout
@end

@implementation LayoutHorizontalBooks
-(void)prepareLayout
    {
    [super prepareLayout];

    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;

    self.minimumInteritemSpacing = 0;
    self.minimumLineSpacing = 0;
    self.itemSize = CGSizeMake(110,130);
    self.sectionInset = UIEdgeInsetsMake(0, 0, 0, 0);
    }