UIViewController extension with functions for showing OnBoarding and setting as 'done' using UserDefaults

UIViewController+Extension.swift

//
//  UIViewController+Extension.swift
//
//  Created by Christian Ascone on 16/06/17.
//

import Foundation
import KVNProgress
import Onboard // https://github.com/mamaral/Onboard

extension UIViewController {

    /// Check if the onboard has been already done
    func isOnboardDone() -> Bool{
        return UserDefaults.standard.bool(forKey: Constants.ONBOARDING_DONE)
    }

    /// Present the onboarding tutorial
    func presentOnboardTutorial() {
        var onboardingVC = OnboardingViewController()
        let firstPage = OnboardingContentViewController(title: nil, body: nil, image: UIImage(named: "pag1"), buttonText: nil) { () -> Void in
            // do something here when users press the button, like ask for location services permissions, register for push notifications, connect to social media, or finish the onboarding process
        }
        let secondPage = OnboardingContentViewController(title: nil, body: nil, image: UIImage(named: "pag2"), buttonText: nil) { () -> Void in
            // do something here when users press the button, like ask for location services permissions, register for push notifications, connect to social media, or finish the onboarding process
        }
        let thirdPage = OnboardingContentViewController(title: nil, body: nil, image: UIImage(named: "pag3"), buttonText: nil) { () -> Void in
            // do something here when users press the button, like ask for location services permissions, register for push notifications, connect to social media, or finish the onboarding process
        }
        let fourthPage = OnboardingContentViewController(title: nil, body: nil, image: UIImage(named: "pag4"), buttonText: nil) { () -> Void in
            // do something here when users press the button, like ask for location services permissions, register for push notifications, connect to social media, or finish the onboarding process
        }
        let fifthPage = OnboardingContentViewController(title: nil, body: nil, image: UIImage(named: "pag5"), buttonText: "Let's go") { () -> Void in
            UserDefaults.standard.set(true, forKey: Constants.ONBOARDING_DONE)
            UserDefaults.standard.synchronize()
            onboardingVC.dismiss(animated: true, completion: nil)
        }

        let contentControllers = [firstPage, secondPage, thirdPage, fourthPage, fifthPage]
        for page in contentControllers {
            page.topPadding = 100
            let aspectRatio = (page.iconImageView.image?.size.width)! / (page.iconImageView.image?.size.height)!
            page.iconWidth = page.view.layer.bounds.width
            page.iconHeight = page.iconWidth / aspectRatio
        }

        // Image
        onboardingVC = OnboardingViewController(backgroundImage: UIImage(named: "onboard_background"), contents: contentControllers)

        self.present(onboardingVC, animated: true, completion: nil)
    }
}