Swift category/extension for animating the switch/swap to a new root view controller at the UIWindow level

UIWindow+AnimatedRootViewController.swift

// Swift category/extension for animating between rootViewControllers at the UIWindow level

import UIKit

extension UIWindow {
    
    func setRootViewController(newRootViewController: UIViewController, animated: Bool) {
        
        // No animation required
        if !animated || self.rootViewController == nil {
            self.rootViewController = newRootViewController
            return
        }
        
        // Snapshot current window and add it as a subview of the new root VC
        let snapshotView = self.snapshotViewAfterScreenUpdates(true)
        newRootViewController.view.addSubview(snapshotView)
        
        // Switch to new root VC
        self.rootViewController = newRootViewController
        
        // Fade out out the snapshot
        UIView.animateWithDuration(0.3, animations: { 
            snapshotView.layer.opacity = 0.0
            snapshotView.layer.transform = CATransform3DMakeScale(1.5, 1.5, 1.5)
            }) { (_) in
                snapshotView.removeFromSuperview()
        }
    }
    
}