ios - 尽管在 IB 中链接，但标签仍为 nil

Question

swift 3/Xcode 8.1

以下代码...

class PageContentVC: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate{

    var array = [String]()
    var currentIndex = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        array = ["1","2","3","4"]

        self.dataSource = self
        self.delegate = self
        self.setViewControllers([helperFunction(index: currentIndex)], direction: .forward, animated: true, completion: nil)

    }

    func helperFunction(index: Int) -> UIViewController{


        let newVC = storyboard?.instantiateViewController(withIdentifier: "PageContent") as! PageContent

        print("currentIndex is: \(currentIndex)")
        print("value at currentIndex is: \(array[currentIndex])")

        newVC.PageContentLabel.text = array[currentIndex]

        return newVC
    }

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

        if (currentIndex ==  0) || (currentIndex == NSNotFound) {
            return nil
        }
        currentIndex -= 1
        return helperFunction(index: currentIndex)
    }

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

        if (currentIndex == array.count - 1) || (currentIndex == NSNotFound) {
            return nil
        }
        currentIndex += 1
        return helperFunction(index: currentIndex) 
    } 
}

...在以下行中使用“Unexpectedly found nil while unwrapping an optional value”错误使应用程序崩溃:
newVC.PageContentLabel.text = array[currentIndex]
“PageContentLabel”肯定是通过界面生成器链接的，当我注释掉有问题的行时，应用程序运行良好。

我在这里想念什么？

Answer 1

标签是 nil因为您已经实例化了 View Controller ，但是 Storyboard中定义的 View 层次结构(如在 IB 中配置的那样)在出现相应 View 之前不会构建。您应该在 View Controller 中添加一个字符串属性并拥有 helperFunction填充它，而不是 IBOutlet .然后，viewDidLoad的 PageContent应该使用该字符串属性并使用它来设置 text的UILabel .最重要的是，在 viewDidLoad 之前不要尝试使用网点。已被调用。