Question

我的应用程序在ios8上运行良好。但是在将所有内容更新到ios9后，我遇到了nill值的问题。我无法弄清楚什么价值是零。这是代码：

func resetToChosenPage(index: Int!) {
    /* Getting the page View controller */
    pageViewController = self.storyboard?.instantiateViewControllerWithIdentifier("PageViewController") as! UIPageViewController
    self.pageViewController.dataSource = self

    pageContentViewController = self.viewControllerAtIndex(index)

    if pageContentViewController != nil {
    self.pageViewController.setViewControllers([pageContentViewController], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: nil)
    }
    /* We are substracting 30 because we have a start again button whose height is 30*/
    self.pageViewController.view.frame = CGRectMake(0, self.navigationController!.navigationBar.frame.height , self.view.frame.width, self.view.frame.height - 30)
    self.addChildViewController(pageViewController)
    self.view.addSubview(pageViewController.view)
    self.pageViewController.didMoveToParentViewController(self)

}

func viewControllerAtIndex(index : Int) -> UIViewController? {


    if((dataArray.count == 0) || (index >= dataArray.count)) {
        return nil
    }
    let pageContentViewController = self.storyboard?.instantiateViewControllerWithIdentifier("SingleArticleViewController") as! SingleArticleViewController

    self.delegate = pageContentViewController
    pageContentViewController.delegate = self
  //  pageContentViewController.delegateWebView = self

    pageContentViewController.singleArticleIndex = index
    pageContentViewController.categoryID = categoryID
    pageContentViewController.dateOfPub = dataArray[index].pubDate
    pageContentViewController.category = dataArray[index].category
    pageContentViewController.newsTitle = dataArray[index].pageTitle
    pageContentViewController.videoLink = dataArray[index].videoLink
    return pageContentViewController
}

一行self.pageViewController.SetViewControllers（[pageContentViewController] ...我有错误＆＃34;致命错误：在解包一个可选值＆＃34;时意外地发现了nil。事实上这个代码在ios8上运行良好。我检查并找不到nil值。此外，我检查了故事板的所有标识符，但它们是正确的。伙计们，如果此代码适用于ios8，会出现什么问题？

Answer 1

我建议尝试更改包含if调用的setViewControllers:子句，以便它显式检查pageContentViewController和pageViewController：

if let pageVC = self.pageViewController, let contentVC = self.pageContentViewController {
    pageVC.setViewControllers([contentVC], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: nil)
}

作为一般情况，我会尽量避免在resetToChosenPage:方法中使用Implicitly Unwrapped Optionals（就像Int !.因为它们会导致这些意外发现的错误。

此外，由于您的resetToChosenPage:方法不检查pageViewController是否已经实例化，因此多次调用它将导致许多PageViewController实例被实例化并堆叠在彼此之上。这可能不是你想要的。

PageViewController不适用于Swift 2.0

1 个答案: