使用 UIPageViewController 在多个视图控制器之间滑动 [英] Swipe between multiple view controllers using UIPageViewController

问题描述

我的 UIPageViewController 根本不工作.我想要做的是在 UIPageViewController 中切换 2 个视图控制器.我已经在这里遵循指南但失败了.

解决方案

尝试访问视图控制器的 restorationIdentifier 时发生崩溃.您使用了 ! 来解开它，但它是 nil ；作为第一个解决方案，在故事板中设置 restorationIdentifier.

<块引用>

一般来说，仅使用 ! 来解开一个值，如果你确定它不是 nil(通过在前面添加一个 if 语句).

My UIPageViewController not working at all. What I'm trying to do is switch 2 view controllers inside UIPageViewController. I already followed guideline here but fail. Using UIPageViewController with swift and multiple view controllers. First view controller appeared successful but when I tried swipe to second view controller it throw this error message. I already set all identifiers correctly.

fatal error: unexpectedly found nil while unwrapping an Optional value

It's cause from here

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

        let identifier = viewController.restorationIdentifier
        let index = self.identifiers.indexOfObject(identifier!) // error message here

        //if the index is 0, return nil since we dont want a view controller before the first one
        if index == 0 {

            return nil
        }

        //decrement the index to get the viewController before the current one
        self.index = self.index - 1
        return self.viewControllerAtIndex(self.index)

    }

Main.storyboard

Source code: https://github.com/datomnurdin/RevivalxSwiftPageViewController

解决方案

The crash occurs while trying to access the restorationIdentifier of your view controller. You used ! to unwrap it but it's nil ; as a first solution, set the restorationIdentifier in the storyboard.

In general, use ! to unwrap a value only if you're sure it's not nil (by adding a if statement just before).

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