Disabling Focus in UICollectionView

MasteringFocusExample4.swift

func collectionView(collectionView: UICollectionView, shouldUpdateFocusInContext context: UICollectionViewFocusUpdateContext) -> Bool {
  guard let indexPaths = collectionView.indexPathsForSelectedItems() else { return true }
  return indexPaths.isEmpty
}

func collectionView(collectionView: UICollectionView, shouldSelectItemAtIndexPath indexPath: NSIndexPath) -> Bool {
  if let indexPath = collectionView.indexPathsForSelectedItems()?.first {
    collectionView.deselectItemAtIndexPath(indexPath, animated: true)
    return false
  }
  else {
    return true
  }
}