ios - 创建无限滚动天数的 UIPageViewController

Question

我的应用程序中有一个由 UIPageViewController 控制的日志。页面的 View Controller 工作正常，但 UIPageViewController 有一些不稳定的行为。首先，委托(delegate)方法(页面 View Controller 是它自己的委托(delegate)):

private func journalPage(for date: Date) -> JournalViewController? {
    // Create a new view controller and pass suitable data.
    guard let journalPage = storyboard?.instantiateViewController(withIdentifier: JournalViewController.storyboardID) as? JournalViewController else {
        return nil
    }

    journalPage.date = date
    return journalPage
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
    guard let yesterday = calendar.date(byAdding: .day, value: -1, to: self.date) else {
        return nil
    }

    self.date = calendar.startOfDay(for: yesterday)        
    return journalPage(for: self.date)
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

    guard let tomorrow = calendar.date(byAdding: .day, value: 1, to: self.date) else {
        return nil
    }

    self.date = calendar.startOfDay(for: tomorrow)
    return journalPage(for: self.date)
}

我更新了 UIPageViewController 的 date，然后返回一个配置的日志页面。问题是经常有重复的页面(同一日期的页面)，或者页面/日期被跳过。我找到了 this问题，但看不出我如何实现类似的东西。

我以前使用过 UIPageViewController 并且一直使用索引来解决这个问题，但在这种情况下索引没有意义，因为您可以滚动到时间的开始/结束(字面意思)。

如何确保在正确的时间制作新页面以避免重复/遗漏日期？

Answer 1

我在没有使用索引的情况下解决了这个问题(页面上的 date 属性就足够了)。这会在任一方向上无限滚动，而不会创建重复项或跳过页面。

extension JournalPageViewController: UIPageViewControllerDataSource {
    /// Creates and returns a JournalViewController if it can be found in the storyboard,
    /// and sets it's date to `date`
    private func journalPage(for date: Date) -> JournalViewController? {
        // Create a new view controller and pass suitable data.
        guard let journalPage = storyboard?.instantiateViewController(withIdentifier: JournalViewController.storyboardID) as? JournalViewController else {
            return nil
        }

        journalPage.date = date
        return journalPage
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        debugPrint("Before: ", separator: "", terminator: "")
        let today = (viewController as! JournalViewController).date
        guard var yesterday = calendar.date(byAdding: .day, value: -1, to: today) else {
            return nil
        }
        yesterday = calendar.startOfDay(for: yesterday)

        return journalPage(for: yesterday)
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        debugPrint("After: ", separator: "", terminator: "")
        let today = (viewController as! JournalViewController).date
        guard var tomorrow = calendar.date(byAdding: .day, value: 1, to: today) else {
            return nil
        }
        tomorrow = calendar.startOfDay(for: tomorrow)

        return journalPage(for: tomorrow)
    }
}

extension JournalPageViewController: UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        self.date = (self.viewControllers?.first as! JournalViewController).date
    }
}