如何使用按钮移动页面视图控制器

Question

我需要使用其他类中的按钮将UIPageViewController移一页。我正在使用Swift 4

    extension OnboardMainViewController: 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 nil }
        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 nil }
        guard pages.count > nextIndex else { return nil }
        return pages[nextIndex]
    }

}

extension OnboardMainViewController: UIPageViewControllerDelegate { }