presentationController.swift

// MARK: - UIViewControllerTransitioningDelegate
extension PaymentInformationRouter: UIViewControllerTransitioningDelegate {
    
    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        return HalfSizePresentationController(presentedViewController: presented, presenting: presenting)
    }
    
}


class HalfSizePresentationController: UIPresentationController {
    
    fileprivate var dimmingView: UIView!
    
    override init(presentedViewController: UIViewController, presenting presentingViewController: UIViewController?) {
        super.init(presentedViewController: presentedViewController, presenting: presentingViewController)
        
        setupDimmingView()
    }
    
    override var frameOfPresentedViewInContainerView: CGRect {
        let height: CGFloat = 391
        let y = containerView!.frame.height - height
        return CGRect(x: 0, y: y, width: containerView!.frame.width, height: height)
    }
    
    override func presentationTransitionWillBegin() {
        super.presentationTransitionWillBegin()
        
        containerView?.insertSubview(dimmingView, at: 0)
        
        NSLayoutConstraint.activate(
            NSLayoutConstraint.constraints(withVisualFormat: "V:|[dimmingView]|",
                                           options: [], metrics: nil, views: ["dimmingView": dimmingView]))
        NSLayoutConstraint.activate(
            NSLayoutConstraint.constraints(withVisualFormat: "H:|[dimmingView]|",
                                           options: [], metrics: nil, views: ["dimmingView": dimmingView]))
        
        guard let coordinator = presentedViewController.transitionCoordinator else {
            dimmingView.alpha = 1.0
            return
        }
        
        coordinator.animate(alongsideTransition: { _ in
            self.dimmingView.alpha = 1.0
        })
    }
    
    override func dismissalTransitionWillBegin() {
        super.dismissalTransitionWillBegin()
        
        guard let coordinator = presentedViewController.transitionCoordinator else {
            dimmingView.alpha = 0.0
            return
        }
        
        coordinator.animate(alongsideTransition: { _ in
            self.dimmingView.alpha = 0.0
        })
    }
    
}


// MARK: - Dim View
extension HalfSizePresentationController {
    
    func setupDimmingView() {
        dimmingView = UIView()
        dimmingView.translatesAutoresizingMaskIntoConstraints = false
        dimmingView.backgroundColor = UIColor.black.withAlphaComponent(0.5)
        dimmingView.alpha = 0.0
    }
    
}