UILabel - 在展开Optional值时意外发现nil

Question

使用此代码动态创建页面，这将创建一个PageViewController

import UIKit

class PageViewController: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {

var pvc:UIPageViewController?
var testArray: [String] = []

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    pvc = UIPageViewController(
            transitionStyle: .Scroll,
            navigationOrientation: .Horizontal,
            options: nil )

    // Make this object the datasource and delegate for the PageViewController
    self.pvc?.delegate = self
    self.pvc?.dataSource = self

    // Populate an array of test content for the pages
    testArray = ["Page 1", "Page 2", "Page 3"]

    // Create an array of child pages
    var swipePage:SwipePageController = SwipePageController()
    println("Page view Controller: \(testArray[0])")
    swipePage.name = testArray[0]
    var pageArray: NSArray = [swipePage]

    self.pvc?.setViewControllers(pageArray, direction: .Forward, animated: true, completion: nil)

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
    let index:Int! = (viewController as SwipePageController).index!

    if (index >= self.testArray.count){
        return nil
    }

    index + 1

    return viewControllerAtIndex(index)

}

func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
    let index:Int! = (viewController as SwipePageController).index!

    if index == NSNotFound {
        return nil
    }

    index - 1

    return viewControllerAtIndex(index)

}

func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
    return self.testArray.count
}

func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {
    let page = self.pvc?.viewControllers[0] as SwipePageController
    let name = page.name
    return find(self.testArray, name!)!
}

func viewControllerAtIndex(index: Int) -> SwipePageController?
{
    if self.testArray.count == 0 || index >= self.testArray.count
    {
        return nil
    }

    // Create a new view controller and pass suitable data.
    let swipeView = SwipePageController()
    swipeView.name = self.testArray[index]
    swipeView.index = index

    return swipeView
}

println（）大约是代码的1/3，显示了我期望看到的值。我动态创建的ViewController的代码在这里：

import UIKit

class SwipePageController: UIViewController {

// var to hold the var to display to the interface
var name:String?
var index:Int?
@IBOutlet weak var testLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    println(name!)
    if let passedName = name? {
        self.testLabel.text = passedName
    }
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


/*
// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
}
*/

}

println（name！）也显示正确的值。但是，我无法使用值填充标签。我收到以下错误：

＆＃34;致命错误：在展开可选值时意外发现nil＆＃34;

我的智慧结束了...我无法弄清楚什么是不起作用的。另外，请参阅发生错误的Xcode界面的屏幕截图：

有人可以帮忙吗？

Answer 1

我认为问题在于您实例化SwipePageController。

而不是：

var swipePage:SwipePageController = SwipePageController()

试试这个：

var swipePage: SwipePageController = UIStoryboard(name: "YourStoryboardName", bundle: nil).instantiateViewControllerWithIdentifier("YourViewControllerId")

将“YourStoryboardName”替换为故事板文件的实际名称，将“YourViewControllerId”替换为滑动页面控制器的Storyboard Id。如果您还没有为其提供Storyboard ID，请确保在Identity检查器中设置它。