UICollectionViewDelegate methods are not taken into account

[yfujiki]

for example, layout.sectionInset = ... or layout.minimumInteritemSpacing = ... works, but implementing delegate methods like

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section

or

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section

don't work.