Can'；I don’我不明白为什么我会；“类ViewController没有初始值设定项”；Swift iOS应用程序代码中存在错误

我试图在我的iOS应用程序中制作一个教程屏幕，用户在屏幕上滑动几张图片，了解一下上述应用程序。一切看起来都很好，除了在构建项目时，在第一行代码中出现以下错误：

类ViewController没有初始值设定项

我做错了什么

下面是我的ViewController.swift代码

import UIKit

//line below is where I get the error

class ViewController: UIViewController, UIPageViewControllerDataSource {

//end

var pageViewController: UIPageViewController
var pageTitles: NSArray!
var pageImages: NSArray!

override func viewDidLoad() {
    super.viewDidLoad()

    self.pageTitles = NSArray(objects: "", "", "")
    self.pageImages = NSArray(objects: "page1", "page2", "page3")

    self.pageViewController = self.storyboard?.instantiateViewControllerWithIdentifier("PageViewController") as!
    UIPageViewController

    self.pageViewController.dataSource = self

    var startVC = self.viewControllerAtIndex(0) as ContentViewController
    var viewControllers = NSArray(object: startVC)

    self.pageViewController.setViewControllers(viewControllers as [AnyObject], direction: .Forward, animated: true, completion: nil)

    self.addChildViewController(self.pageViewController)
    self.view.addSubview(self.pageViewController.view)
    self.pageViewController.didMoveToParentViewController(self)

}

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

@IBAction func restartAction(sender: AnyObject) {
}

func viewControllerAtIndex(index: Int) -> ContentViewController
{

    if ((self.pageTitles.count == 0) || (index >= self.pageTitles.count))
    {
        return ContentViewController()
    }

    var vc: ContentViewController = self.storyboard?.instantiateViewControllerWithIdentifier("ContentViewController") as! ContentViewController

    vc.imageFile = self.pageImages[index] as! String
    vc.titleText = self.pageTitles[index] as! String

    vc.pageIndex = index

    return vc

}

// Mark: - Page View Controller Data Source

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

    var vc = viewController as! ContentViewController
    var index = vc.pageIndex as Int

    if (index == 0 || index == NSNotFound)
    {
        return nil
    }

    index--
    return self.viewControllerAtIndex(index)

}

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

    var vc = viewController as! ContentViewController
    var index = vc.pageIndex as Int

    if (index == NSNotFound)
    {
        return nil
    }

    index++

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

    return self.viewControllerAtIndex(index)
}

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

func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {
    return 0
}

}

---

因为这一行：

var pageViewController: UIPageViewController

您的意思是

pageViewController

不能为null，但您没有将其设置为值的初始值设定项。查看您的代码，我怀疑您想将其更改为：

var pageViewController: UIPageViewController!

---

在Swift类中，每个非可选声明变量必须在给定的init方法之一中初始化

在你的例子中，就是这个变量

 var pageViewController: UIPageViewController

与其他两个变量一样，将其声明为隐式unwrapped optional，因为该变量保证在使用之前进行设置

 var pageViewController: UIPageViewController!

---

不客气。别忘了：如果你把答案标记为正确的，它也会帮助其他人。我本来打算这样做的，但是StackOverflow让我等几分钟：）另请看