당겨서 닫을 수있는 모달 구현 (UINavigationController의 경우)

UIKit에서는 ViewController → ViewController 전환을 사용자 정의할 수 있습니다.
위 이미지처럼 버튼을 누르면 아래에서 나와서 당기면 닫을 수 있는 모달을 구현해 봅니다.

당초 이쪽의 튜토리얼을 참고로 진행하고 있었습니다만, 어떤 문제가 발생했습니다.
UINavigationController에 Pan Gesture Recognizer를 연결할 수 없다는 것입니다.
그래서 UINavigationController의 아이의 ViewController로 Pan Gesture를 핸들링해, UINavigationController에 전파하는 방법으로 목적을 달성할 수 있었으므로 코드 조각을 남겨 두고 싶습니다.

파일 구성

ViewController

ModalNavigationController

ModalViewController

DismissAnimator

Interactor

코드

ViewController.swift

import UIKit

class ViewController: UIViewController, UIViewControllerTransitioningDelegate {
    let interactor = Interactor()

    @IBAction func handleButton(_ sender: UIButton) {
        let sb = UIStoryboard(name: "ModalViewController", bundle: nil)
        let nc = sb.instantiateInitialViewController() as! ModalNavigationController
        nc.interactor = interactor
        nc.transitioningDelegate = self
        present(nc, animated: true, completion: nil)
    }

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

    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactor.hasStarted ? interactor : nil
    }
}

ModalNavigationController.swift

import UIKit

class ModalNavigationController: UINavigationController {
    var interactor: Interactor!

    func handleGesture(_ sender: UIPanGestureRecognizer) {
        let percentThreshold: CGFloat = 0.3

        let translation = sender.translation(in: view)
        let verticalMovement = translation.y / view.bounds.height
        let downwardMovement = fmaxf(Float(verticalMovement), 0.0)
        let downwardMovementPercent = fminf(downwardMovement, 1.0)
        let progress = CGFloat(downwardMovementPercent)

        switch sender.state {
        case .began:
            interactor.hasStarted = true
            dismiss(animated: true, completion: nil)
        case .changed:
            interactor.shouldFinish = progress > percentThreshold
            interactor.update(progress)
        case .cancelled:
            interactor.hasStarted = false
            interactor.cancel()
        case .ended:
            interactor.hasStarted = false
            interactor.shouldFinish
                ? interactor.finish()
                : interactor.cancel()
        default:
            break
        }
    }
}

ModalViewController.swift

import UIKit

class ModalViewController: UIViewController {
    @IBAction func handleDismissButton(_ sender: UIBarButtonItem) {
        dismiss(animated: true, completion: nil)
    }

    @IBAction func handleGesture(_ sender: UIPanGestureRecognizer) {
        weak var nc = navigationController as? ModalNavigationController
        nc?.handleGesture(sender)
    }
}

DismissAnimator.swift

import UIKit

class DismissAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 1.0
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard
            let fromVC = transitionContext.viewController(forKey: .from),
            let toVC = transitionContext.viewController(forKey: .to)
        else { return }

        let containerView = transitionContext.containerView

        containerView.insertSubview(toVC.view, belowSubview: fromVC.view)

        let screenBounds = UIScreen.main.bounds
        let bottomLeftCorner = CGPoint(x: 0, y: screenBounds.height)
        let finalFrame = CGRect(origin: bottomLeftCorner, size: screenBounds.size)

        UIView.animate(
            withDuration: transitionDuration(using: transitionContext),
            animations: {
                fromVC.view.frame = finalFrame
            },
            completion: { _ in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            }
        )
    }
}

Interactor.swift

import UIKit

class Interactor: UIPercentDrivenInteractiveTransition {
    var hasStarted = false
    var shouldFinish = false
}

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