Custom Fade In/Out Segue

custom_segue.swift

import UIKit

// All you do is assign this class to a segue in your storyboard and you're done

class BottomCardSegue: UIStoryboardSegue {
    
    private var selfRetainer: BottomCardSegue? = nil
    
    override func perform() {
        destination.transitioningDelegate = self
        selfRetainer = self
        destination.modalPresentationStyle = .overCurrentContext
        source.present(destination, animated: true, completion: nil)
    }
}

extension BottomCardSegue: UIViewControllerTransitioningDelegate {
    public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return TransitioningAnimatorIn()
    }
    
    public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        selfRetainer = nil
        return TransitioningAnimatorOut()
    }
}

class TransitioningAnimatorIn: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard
            let toViewController = transitionContext.viewController(forKey: .to)
            else {
                return
        }
        transitionContext.containerView.addSubview(toViewController.view)
        toViewController.view.alpha = 0
        
        let duration = self.transitionDuration(using: transitionContext)
        UIView.animate(withDuration: duration, animations: {
            toViewController.view.alpha = 1
        }, completion: { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        })
    }
}

class TransitioningAnimatorOut: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard
            let fromViewController = transitionContext.viewController(forKey: .from)
            else {
                return
        }
        
        let duration = self.transitionDuration(using: transitionContext)
        UIView.animate(withDuration: duration, animations: {
            fromViewController.view.alpha = 0
        }, completion: { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        })
    }
}