CustomUnwindSegue.swift

import UIKit

class CustomUnwindSegue: UIStoryboardSegue {
    override func perform(){
        //遷移前のViewControllerのインスタンスを作成
        let firstVC = self.source
        //遷移後のViewControllerのインスタンスを作成
        let secondVC = self.destination
        
        let mock = createMockView(view: firstVC.view)
        secondVC.view.addSubview(mock)
        
        //画面の横の長さを取得
        let width = UIScreen.main.bounds.size.width
        //画面の縦の長さを取得
        let height = UIScreen.main.bounds.size.height
        
        mock.frame = CGRect(x:0,y:0,width:width,height:height)
        
        //先にdismissをする
        self.source.dismiss(animated: false, completion: {
            UIView.animate(withDuration: 0.5, animations: {
                mock.frame.origin.x = width
            }) { (isCompletion) in
                mock.removeFromSuperview()
            }
        })

    }
    
    func createMockView(view: UIView) -> UIImageView {
        UIGraphicsBeginImageContextWithOptions(view.frame.size, true, UIScreen.main.scale)
        
        view.drawHierarchy(in: view.bounds, afterScreenUpdates: true)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        
        UIGraphicsEndImageContext()
        return UIImageView(image: image)
    }
}