transition.swift

class TransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
    
    var openingFrame: CGRect?
    
    func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let presentationAnimator = PresentationAnimator()
        presentationAnimator.openingFrame = openingFrame!
        return presentationAnimator
    }
    
    func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let dismissAnimator = DismissalAnimator()
        dismissAnimator.openingFrame = openingFrame!
        return dismissAnimator
    }
}

class PresentationAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    
    var openingFrame: CGRect?
    
    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.5
    }
    
    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let toViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let containerView = transitionContext.containerView()
        
        let animationDuration = self.transitionDuration(transitionContext)
        
        let fromViewFrame = fromViewController.view.frame
        
        UIGraphicsBeginImageContext(fromViewFrame.size)
        fromViewController.view.drawViewHierarchyInRect(fromViewFrame, afterScreenUpdates: true)
        let _ = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        let snapshotView = toViewController.view.resizableSnapshotViewFromRect(toViewController.view.frame, afterScreenUpdates: true, withCapInsets: UIEdgeInsetsZero)
        snapshotView.frame = openingFrame!
        containerView?.addSubview(snapshotView)
        
        toViewController.view.alpha = 0.0
        containerView?.addSubview(toViewController.view)
        
        UIView.animateWithDuration(animationDuration, delay: 0.0, usingSpringWithDamping: 0.8, initialSpringVelocity: 20.0, options: [], animations: {
            snapshotView.frame = fromViewController.view.frame
            }) { (finished) in
                snapshotView.removeFromSuperview()
                toViewController.view.alpha = 1.0
                transitionContext.completeTransition(finished)
        }
    }
}


// CALLED IN:

override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
        collectionView.deselectItemAtIndexPath(indexPath, animated: true)
        
        let cell = collectionView.cellForItemAtIndexPath(indexPath) as! TierCollectionViewCell
        
        let attributes = collectionView.layoutAttributesForItemAtIndexPath(indexPath)
        let attributesFrame = attributes?.frame
        let frameToOpenFrom = collectionView.convertRect(attributesFrame!, toView: collectionView.superview)
        transitionDelegate.openingFrame = frameToOpenFrom
        
        let detailViewController = storyboard?.instantiateViewControllerWithIdentifier("tierListDetailViewController") as! TierListDetailViewController
        detailViewController.transitioningDelegate = transitionDelegate
        detailViewController.modalPresentationStyle = .Custom
        presentViewController(detailViewController, animated: true, completion: nil)
    }



class DismissalAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    
    var openingFrame: CGRect?
    
    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.5
    }
    
    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let toViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let containerView = transitionContext.containerView()
        
        let animationDuration = self.transitionDuration(transitionContext)
        
        let snapshotView = fromViewController.view.resizableSnapshotViewFromRect(fromViewController.view.bounds, afterScreenUpdates: true, withCapInsets: UIEdgeInsetsZero)
        containerView?.addSubview(snapshotView)
        
        fromViewController.view.alpha = 0.0
        
        UIView.animateWithDuration(animationDuration, animations: { 
            snapshotView.frame = self.openingFrame!
            snapshotView.alpha = 0.0
            }) { (finished) in
                snapshotView.removeFromSuperview()
                fromViewController.view.removeFromSuperview()
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled())
        }
    }
}