swift 4 UIPageViewControler

Question

У меня есть три ViewController a, b, c. Я хочу инициализировать первый viewController как (b), затем проведите пальцем влево к viewController (a) и проведите пальцем вправо для viewController (c)

как сделать это с помощью UIPageViewController

Answer 1

У вас должно быть 3 ViewController с идентификаторами Page1,Page2 & Page3 в Main.storyboard.

import UIKit

class PageViewController: UIPageViewController
{
    fileprivate lazy var pages: [UIViewController] = {
        return [
            self.getViewController(withIdentifier: "Page1"),
            self.getViewController(withIdentifier: "Page2"),
            self.getViewController(withIdentifier: "Page3")
        ]
    }()

    fileprivate func getViewController(withIdentifier identifier: String) -> UIViewController
    {
        return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: identifier)
    }

    override func viewDidLoad()
    {
        super.viewDidLoad()
        self.dataSource = self
        self.delegate   = self

        if let firstVC = pages.first
        {
            setViewControllers([firstVC], direction: .forward, animated: true, completion: nil)
        }
    }
}

extension PageViewController: UIPageViewControllerDataSource
{
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

        guard let viewControllerIndex = pages.index(of: viewController) else { return nil }

        let previousIndex = viewControllerIndex - 1

        guard previousIndex >= 0          else { return pages.last }

        guard pages.count > previousIndex else { return nil        }

        return pages[previousIndex]
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController?
    {
        guard let viewControllerIndex = pages.index(of: viewController) else { return nil }

        let nextIndex = viewControllerIndex + 1

        guard nextIndex < pages.count else { return pages.first }

        guard pages.count > nextIndex else { return nil         }

        return pages[nextIndex]
    }
}

extension PageViewController: UIPageViewControllerDelegate { }