PercentageTransitionAnimator.swift

final class InteractiveSwipe: UIPercentDrivenInteractiveTransition {

    var panGesture: UIPanGestureRecognizer?
    weak var viewController: UIViewController?

    private var shouldComplete = true

    func attachToViewController(viewController: UIViewController) {
        self.viewController = viewController
        panGesture = UIPanGestureRecognizer(target:self, action: "onPan:")
        self.viewController?.view.addGestureRecognizer(panGesture!)
    }

    func onPan(pan: UIPanGestureRecognizer) {
        let translation = pan.translationInView(pan.view?.superview)

        switch pan.state {

        case .Began: break
            self.viewController?.dismissViewControllerAnimated(true, completion: nil)

        case .Changed:
            let dragAmount: CGFloat = 50
            let threshHold: CGFloat = 0.5
            var percentage: CGFloat = translation.x / dragAmount
            percentage = CGFloat(fmaxf(Float(percentage), 0.0))
            percentage = CGFloat(fminf(Float(percentage), 1.0))

            self.updateInteractiveTransition(percentage)
            shouldComplete = percentage >= threshHold
            print(shouldComplete)
            print(percentage)
        case .Ended:
            self.finishInteractiveTransition()

        case .Cancelled:
            self.cancelInteractiveTransition()

        default:
            return
        }
    }

    @nonobjc
    func completionSpeed() -> CGFloat {
        return 1 - self.percentComplete
    }
}