Small function to get the App Delegate of any iOS app

AppDelegate.swift

//
//  AppDelegate.swift
//
//  Created by Rigoberto Sáenz Imbacuán (https://www.linkedin.com/in/rsaenzi/)
//  Copyright © 2019. All rights reserved.
//

extension AppDelegate {
    
    static func getDelegate() -> AppDelegate {
        return UIApplication.shared.delegate as! AppDelegate
    }
}

func setScreenAsRoot() {

    guard let window = AppDelegate.getDelegate().window else {
        return
    }

    // Loads the navigation controller in which Welcome screen is embed in
    guard let screen: UINavigationController = WelcomeVC.loadFirstViewController() as? UINavigationController else {
        return
    }

    // Makes that nav controller the root
    window.rootViewController = screen
    UIView.transition(with: window, duration: 0.5, options: .transitionCrossDissolve, animations: nil, completion: nil)
}