medium-peekandpoppost-1.swift

@available(iOS 9.0, *)
extension TwitterFeedViewController: UIViewControllerPreviewingDelegate {
       public func previewingContext(previewingContext: UIViewControllerPreviewing, viewControllerForLocation location: CGPoint) -> UIViewController? {
           guard let indexPath = collectionView.indexPathForItemAtPoint(location),
           cell = collectionView.cellForItemAtIndexPath(indexPath),
           let tweet = viewModel.tweetAtIndexPath(indexPath) else { return nil }
           //now we are ready to create our corresponding controller for the tweet
           let tweetViewController = self.navigationCoordinationController.tweetControllerForTweet(tweet)
           //I will expand on this in a bit but this lets us present controllers using peek and pop actions
           tweetViewController.initiatingPreviewActionController = self
           //lets the system dictate the size
           tweetViewController.preferredContentSize = CGSize.zero
           //Shows the tweet controller right over our cell. Changing this will change where the controller is peeked from.
           tweetViewController.sourceRect = cell.frame
           return tweetViewController
    }
    
    public func previewingContext(previewingContext: UIViewControllerPreviewing, commitViewController viewControllerToCommit: UIViewController) {
        showViewController(viewControllerToCommit, sender: nil)
    }
}