无法弄清楚为什么我在 Swift iOS 应用程序代码中收到"Class ViewController has no initializers"错误

Question

我试图在我的iOS应用程序中制作一个教程屏幕，用户可以在其中浏览几张图片来了解上述应用程序。一切看起来都很好，除了当我构建项目时，我在代码的第一行就出现了以下错误：

类视图控制器没有初始化程序

我做错了什么？

我的ViewController.swift代码低于

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
}
}

Answer 1

这是因为这行：

var pageViewController: UIPageViewController

您说pageViewController不能为null，但您没有将其设置为值的初始值设定项。看看你的代码，我怀疑你想把它改成这样：

var pageViewController: UIPageViewController!

我在这里详细介绍了这个问题。

Answer 2

在Swift类中，每个非可选的声明变量都必须在给定的init方法之一中初始化。

在你的情况下，是这个变量

 var pageViewController: UIPageViewController

将其声明为隐式展开的可选变量(与其他两个变量一样(，因为保证在使用变量之前对其进行设置。

 var pageViewController: UIPageViewController!