SlideOutTransitioning.swift

import UIKit

class SlideOutTransitioning: NSObject, UIViewControllerTransitioningDelegate, UIViewControllerAnimatedTransitioning {

    private var presenting: Bool = false
    private let duration = 0.3

    func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        self.presenting = true
        return self
    }

    func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        self.presenting = false
        return self
    }

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning) -> NSTimeInterval {
        return duration
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        if presenting {
            present(transitionContext)
        } else {
            dismiss(transitionContext)
        }
    }

    private func animate(animations: ()->(), completion: (Bool)->()) {
        UIView.animateWithDuration(duration,
            delay: 0.0,
            usingSpringWithDamping: 0.8,
            initialSpringVelocity: 0.0,
            options: UIViewAnimationOptions.BeginFromCurrentState,
            animations: animations,
            completion: completion)
    }

    private func present(transitionContext: UIViewControllerContextTransitioning) {
        let to = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)!
        let from = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let preferredWidth = to.preferredContentSize.width
        let maxWidth = from.view.frame.width
        let width = preferredWidth == 0 ? maxWidth : min(preferredWidth, maxWidth)
        let (endFrame, _) = from.view.frame.rectsByDividing(width, fromEdge: .MaxXEdge)
        to.view.frame = endFrame
        to.view.transform = CGAffineTransformMakeTranslation(width, 0)
        from.view.userInteractionEnabled = false
        transitionContext.containerView().addSubview(to.view)
        animate({
            from.view.tintAdjustmentMode = .Dimmed
            to.view.transform = CGAffineTransformIdentity
        }, completion: { completed in
            transitionContext.completeTransition(completed)
        })
    }

    private func dismiss(transitionContext: UIViewControllerContextTransitioning) {
        let to = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)!
        let from = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
        let width = from.view.frame.width
        transitionContext.containerView().addSubview(from.view)
        to.view.userInteractionEnabled = true
        animate({
            to.view.tintAdjustmentMode = .Automatic
            from.view.transform = CGAffineTransformMakeTranslation(width, 0)
        }, completion: { completed in
            transitionContext.completeTransition(completed)
        })
    }

}