Hello ! I was studying swift by Apple's book "Develop in swift Data Collections" and in some projects book provided server application to which in IOS app were made url requests to send and receive data. How can I create such server using swift and xcode without any frameworks or external libraries ?

When PageController trying to present it's content I'm encountering following message in console: "[Assert] Window should be nonnil here unless a subclass is mistakenly sending this to a child when no window can be found". App is not crashing it's just not showing content it's supposed to show in PageController. Code seems fine to me: class RulesPageViewController: UIPageViewController { var rulesDelegate: RulesPageVeiwControllerDelegate? var pageHeadings = ["1st page","2nd","3rd"] var currentIndex = 0 override func viewDidLoad() { super.viewDidLoad() self.dataSource = self self.delegate = self if let startingViewController = contentViewController(at: 0) { self.setViewControllers([startingViewController], direction: .forward, animated: false, completion: nil) } } func contentViewController(at index: Int)-> PageContentViewController? { if(index < 0 || index >= pageHeadings.count) { return nil } if let pageContentViewController = UIStoryboard(name: "GameRules", bundle: nil).instantiateViewController(withIdentifier: "PageContentViewController") as? PageContentViewController{ pageContentViewController.index = index return pageContentViewController } return nil } } extension RulesPageViewController: UIPageViewControllerDelegate { func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) { if completed { if let contentViewController = pageViewController.viewControllers?.first as? PageContentViewController { currentIndex = contentViewController.index rulesDelegate?.didUpdatePageIndex(currentIndex: currentIndex) } } } } extension RulesPageViewController: UIPageViewControllerDataSource { func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? { var index = (viewController as! PageContentViewController).index index -= 1 return contentViewController(at: index) } func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? { var index = (viewController as! PageContentViewController).index index += 1 return contentViewController(at: index) } }