Custom UIViewController transition. Supports pop and modal transition.

ModalPresentationAnimator.swift

import UIKit

extension ModalPresentationAnimator {
    enum Mode {
        case present
        case dismiss
    }
    enum AnimationStyle {
        case modal
        case pop
    }
    enum SizeMode {
        case automatic
        case manual(size: CGSize)
    }
}

class ModalPresentationAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    
    var duration: TimeInterval = 0.5
    var mode: Mode = .present
    var animationStyle: AnimationStyle = .modal
    var darkness: CGFloat = 0.5
    var sizeMode: SizeMode = .automatic
    
    private lazy var backgroundView: UIView = {
        let view = UIView(frame: .zero)
        view.backgroundColor = UIColor.black.withAlphaComponent(darkness)
        return view
    }()
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return duration
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let containerView = transitionContext.containerView
        let fromView = transitionContext.view(forKey: .from)
        let toView = transitionContext.view(forKey: .to)
        
        switch mode {
        case .present:
            guard let toView = toView else { return }
            containerView.addSubview(backgroundView)
            backgroundView.frame = containerView.bounds
            backgroundView.alpha = 0
            containerView.addSubview(toView)
            let size: CGSize
            switch sizeMode {
            case .automatic:
                size = toView.systemLayoutSizeFitting(CGSize(width: containerView.frame.width - 50, height: UIView.layoutFittingCompressedSize.height), withHorizontalFittingPriority: UILayoutPriority.required, verticalFittingPriority: UILayoutPriority.defaultLow)
            case .manual(size: let mSize):
                size = mSize
            }
            toView.frame.size = size
            
            switch animationStyle {
            case .modal:
                toView.center = CGPoint(x: containerView.center.x, y: containerView.frame.height + toView.frame.height/2)
            case .pop:
                toView.center = containerView.center
                toView.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)
                toView.alpha = 0
            }
            toView.layer.cornerRadius = 16
            
            UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: UIView.AnimationOptions.curveEaseInOut, animations: {
                toView.center = containerView.center
                if self.animationStyle == .pop {
                    toView.transform = .identity
                    toView.alpha = 1
                }
                self.backgroundView.alpha = 1
            }) { (success) in
                transitionContext.completeTransition(success)
            }
            
        case .dismiss:
            guard let fromView = fromView else { return }
            UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
                switch self.animationStyle {
                case .modal:
                    fromView.center = CGPoint(x: containerView.center.x, y: containerView.frame.height + fromView.frame.height/2)
                case .pop:
                    fromView.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)
                    fromView.alpha = 0
                }
                self.backgroundView.alpha = 0
            }) { (success) in
                self.backgroundView.removeFromSuperview()
                transitionContext.completeTransition(success)
            }
        }
    }
    
}