ViewController.swift

import UIKit

class ViewController: UIViewController, UIPageViewControllerDataSource {
    
    // MARK: - Variables
    private var pageViewController: UIPageViewController?
    
    // Initialize it right away here
    private let contentImages = ["nature_pic_1",
                                 "nature_pic_2",
                                 "nature_pic_3",
                                 "nature_pic_4"]
}