Adding the page view controller

To display the city's information, we are going to use a page view controller. This way, we can navigate through its information as if we were reading a book. To do it, we are going to add a new file called CityOptionsViewController.swift to the ViewControllers group.

Open this file and create a class that inherits from UIPageViewController and also stores CityInfo. This class should also be its own data source, as it needs to know which view controller comes next when the user decides to turn a page. As we don't yet have any of the view controllers that are going to hang from this page view controller, we are going to implement the mandatory methods that will return nil. Let's start implementing the CityOptionsViewController class with a minimum code by typing the following code:

import UIKit

class CityOptionsViewController : UIPageViewController, UIPageViewControllerDataSource {
    var cityInfo:CityInfo!
    override func viewDidLoad() {
        super.viewDidLoad...