ios - 为什么 PageViewController 中的代码出现两次？

Question

我正在 createViewController() 方法中创建 pageViewController。我已经定义了 UIPageViewController 的一个属性，它是 self.pageController。由于重复的代码块，当这些页面打开时，当我们离开滚动页面时，它也会显示在 View 后面。

func createPageController()
    {
        var deviceFrame:CGSize = UIScreen.mainScreen().bounds.size
        self.pageController = UIPageViewController(transitionStyle: UIPageViewControllerTransitionStyle.Scroll,
            navigationOrientation: UIPageViewControllerNavigationOrientation.Horizontal,
            options: [UIPageViewControllerOptionInterPageSpacingKey : 0])

            self.pageController!.view.frame = CGRectMake(0,108, deviceFrame.width, deviceFrame.height-110)
            self.dailyChallengeViewController = UIStoryboard(name: "Main_iPhone", bundle: nil).instantiateViewControllerWithIdentifier("DailyChallengeViewController") as? DailyChallengeViewController
            self.winnersViewController = UIStoryboard(name: "Main_iPhone", bundle: nil).instantiateViewControllerWithIdentifier("WinnersViewController") as? WinnersViewController

// All the below code will repeat 1 more time
 self.winnersViewController!.view.frame = self.pageController!.view.frame
        self.dailyChallengeViewController!.view.frame = self.pageController!.view.frame

        self.dailyChallengeViewController!.index = 0
        self.winnersViewController!.index = 1

        self.viewControllers = [self.dailyChallengeViewController!,self.winnersViewController!]
        self.pageController!.setViewControllers([self.dailyChallengeViewController!],
            direction:UIPageViewControllerNavigationDirection.Forward,
            animated:false,
            completion:nil)
        self.addChildViewController(self.pageController!)

        self.view.addSubview(self.pageController!.view)

        self.pageController!.dataSource = self
        self.pageController!.delegate = self

 self.pageController!.didMoveToParentViewController(self)
}

func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController?{
}

func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController?{
}

Answer 1

据我所知，很多人都有这个问题。

这是因为 viewControllerBeforeViewController 和 viewControllerAfterViewController。

建议使用 willTransitionToViewControllers 与上述其他两种方法一起获取 PVC 的当前索引。

换句话说，如果您希望在索引 x 处发生特定的事情，请在 willTransitionToViewControllers 委托(delegate)方法中编写一个 if 语句。

希望对你有帮助!

PageViewController delegate functions called twice