UICollection View causes "UICollectionViewFlowLayoutBreakForInvalidSizes" on smaller devices

By confirming UICollectionViewDelegate from your class. The delegate method sizeForItemAtIndexPath will call from UICollectionViewDelegateFlowLayout and this will call in your class now you can return the size of UICollectionViewCell.

This works for me

method:

collectionView.delegate = self

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
     return CGSizeMake(collectionView.frame.size.width, collectionView.frame.size.height)
}