how-to-use.swift

class MyViewController: UIViewController {

	func showMenuFromBottom() {
		let menuViewController = MyMenuViewController()
		let cardViewController = InteractiveModalCardViewController()
		cardViewController.install(
			menuViewController, panGestureRecognizer: menuViewController.dismissGestureRecognizer)
		present(cardViewController, animated: true, completion: nil)
	}

}

InteractiveModalCardViewController.swift

//
//  InteractiveModalCardViewController.swift
//  Eastwatch
//
//  Created by Shane Qi on 1/14/19.
//  Copyright © 2019 Shane Qi. All rights reserved.
//

import UIKit

final class InteractiveModalCardViewController: UIViewController {

	private let visualEffectView: UIVisualEffectView = {
		let view = UIVisualEffectView(effect: UIBlurEffect(style: .dark))
		view.alpha = 0
		view.translatesAutoresizingMaskIntoConstraints = false
		return view
	} ()
	private let cardContainer: UIView = {
		let view = UIView()
		view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
		view.layer.cornerRadius = 16
		view.clipsToBounds = true
		view.translatesAutoresizingMaskIntoConstraints = false
		return view
	} ()
	private let backgroundTappingRecognizer = UITapGestureRecognizer()

	private var hiddingCardConstraint: NSLayoutConstraint?
	private var showingCardConstraint: NSLayoutConstraint?
	private var animator: UIViewPropertyAnimator?
	private var isDismissingInteractively: Bool?
	private var transitionContext: UIViewControllerContextTransitioning?
	private var dismissGestureTotalDistance: CGFloat?

	override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
		super.init(nibName: nil, bundle: nil)
		transitioningDelegate = self
		modalPresentationStyle = .overFullScreen
	}

	required init?(coder aDecoder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}

	override func viewDidLoad() {
		super.viewDidLoad()
		view.addGestureRecognizer(backgroundTappingRecognizer)
		backgroundTappingRecognizer.addTarget(self, action: #selector(didTapBackground(_:)))
		view.addSubview(visualEffectView)
		NSLayoutConstraint.activate([
			visualEffectView.leftAnchor.constraint(equalTo: view.leftAnchor),
			visualEffectView.rightAnchor.constraint(equalTo: view.rightAnchor),
			visualEffectView.topAnchor.constraint(equalTo: view.topAnchor),
			visualEffectView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
			])
		view.addSubview(cardContainer)
		showingCardConstraint = cardContainer.bottomAnchor.constraint(equalTo: view.bottomAnchor)
		hiddingCardConstraint = cardContainer.topAnchor.constraint(equalTo: view.bottomAnchor)
		NSLayoutConstraint.activate([
			cardContainer.leftAnchor.constraint(equalTo: view.leftAnchor),
			cardContainer.rightAnchor.constraint(equalTo: view.rightAnchor),
			hiddingCardConstraint
			].compactMap({ $0 }))
	}

	func install(_ viewController: UIViewController, panGestureRecognizer: UIPanGestureRecognizer) {
		addChild(viewController)
		cardContainer.addSubview(viewController.view)
		viewController.view.translatesAutoresizingMaskIntoConstraints = false
		NSLayoutConstraint.activate([
			viewController.view.leftAnchor.constraint(equalTo: cardContainer.leftAnchor),
			viewController.view.rightAnchor.constraint(equalTo: cardContainer.rightAnchor),
			viewController.view.topAnchor.constraint(equalTo: cardContainer.topAnchor),
			viewController.view.bottomAnchor.constraint(equalTo: cardContainer.bottomAnchor)
			])
		viewController.didMove(toParent: self)
		panGestureRecognizer.addTarget(self, action: #selector(didChange(dismissGestureRecognizer:)))
	}

	@objc private func didTapBackground(_ gestureRecognizer: UITapGestureRecognizer) {
		let location = gestureRecognizer.location(in: cardContainer.superview)
		guard !cardContainer.frame.contains(location) else {
			return
		}
		isDismissingInteractively = false
		dismiss(animated: true, completion: nil)
	}

	@objc private func didChange(dismissGestureRecognizer recognizer: UIPanGestureRecognizer) {
		switch recognizer.state {
		case .began:
			dismissGestureTotalDistance = cardContainer.frame.height
			isDismissingInteractively = true
			dismiss(animated: true, completion: nil)
			recognizer.setTranslation(.zero, in: view)
		case .changed:
			guard let animator = animator, let context = transitionContext,
				let totalDistance = dismissGestureTotalDistance else { break }
			let deltaY = recognizer.translation(in: view).y
			var deltaFractionCompletion = deltaY / totalDistance
			if deltaFractionCompletion > 1 {
				deltaFractionCompletion = 1
			} else if deltaFractionCompletion < 0 {
				deltaFractionCompletion = 0
			}
			animator.fractionComplete = deltaFractionCompletion
			context.updateInteractiveTransition(deltaFractionCompletion)
		case .cancelled, .ended:
			guard let animator = animator else { break }
			if animator.fractionComplete < 0.5, recognizer.velocity(in: view).y < 500 {
				transitionContext?.cancelInteractiveTransition()
				animator.isReversed = true
			} else {
				transitionContext?.finishInteractiveTransition()
			}
			animator.continueAnimation(
				withTimingParameters: UISpringTimingParameters(dampingRatio: 1), durationFactor: 0.5)
		default: break
		}
	}

}

extension InteractiveModalCardViewController: UIViewControllerTransitioningDelegate {

	func animationController(
		forPresented presented: UIViewController,
		presenting: UIViewController,
		source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
		return self
	}

	func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
		return self
	}

	func interactionControllerForDismissal(
		using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
		if isDismissingInteractively == true {
			return self
		} else {
			return nil
		}
	}

}

extension InteractiveModalCardViewController: UIViewControllerAnimatedTransitioning {

	var transitionDuration: TimeInterval {
		return 0.25
	}

	func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
		return transitionDuration
	}

	func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
		if let toView = transitionContext.view(forKey: .to), toView === view {
			view.layoutIfNeeded()
			transitionContext.containerView.addSubview(toView)
			UIView.animate(withDuration: transitionDuration, animations: {
				self.visualEffectView.alpha = 1
				self.hiddingCardConstraint?.isActive = false
				self.showingCardConstraint?.isActive = true
				self.view.layoutIfNeeded()
			}, completion: { _ in
				transitionContext.completeTransition(true)
			})
		} else {
			UIView.animate(withDuration: transitionDuration, animations: {
				self.visualEffectView.alpha = 0
				self.cardContainer.alpha = 0
				self.showingCardConstraint?.isActive = false
				self.hiddingCardConstraint?.isActive = true
				self.view.layoutIfNeeded()
			}, completion: { _ in
				self.isDismissingInteractively = nil
				transitionContext.completeTransition(true)
			})
		}
	}

}

extension InteractiveModalCardViewController: UIViewControllerInteractiveTransitioning {

	func startInteractiveTransition(_ transitionContext: UIViewControllerContextTransitioning) {
		self.transitionContext = transitionContext
		animator = UIViewPropertyAnimator(duration: transitionDuration, curve: .linear) {
			self.visualEffectView.alpha = 0
			self.cardContainer.alpha = 0
			self.showingCardConstraint?.isActive = false
			self.hiddingCardConstraint?.isActive = true
			self.view.layoutIfNeeded()
		}
		animator?.addCompletion { position in
			self.isDismissingInteractively = nil
			switch position {
			case .end:
				transitionContext.completeTransition(true)
			default:
				self.cardContainer.alpha = 1
				self.visualEffectView.alpha = 1
				self.hiddingCardConstraint?.isActive = false
				self.showingCardConstraint?.isActive = true
				transitionContext.completeTransition(false)
			}
		}
		animator?.pauseAnimation()
	}

}