PreviewingContextMethod.swift

func previewingContext(_ previewingContext: UIViewControllerPreviewing, viewControllerForLocation location: CGPoint) -> UIViewController? {
  guard let indexPath = collectionView.indexPathForItem(at: location),
    let cell = collectionView.cellForItem(at: indexPath) else { return nil }
    
  guard let detailViewController = storyboard?.instantiateViewControllerWithIdentifier("ColorViewController") as? ColorViewController else { return nil }
    
  detailViewController.preferredContentSize = CGSize(width: 300, height: 300)
  detailViewController.color = colors[indexPath.row]
    
  previewingContext.sourceRect = cell.frame
    
  return detailViewController
}