Swift:类型'ViewController‘不符合协议'UIPageViewControllerDataSource’

Question

我用的是Xcode6GM。我正在尝试实现这个page view controller tutorial，但是使用Swift而不是Objective-C，但是它并没有像预期的那样工作。

我已经设法解决了大多数问题，除了在实现UIPageViewControllerDataSource协议时的协议一致性问题。

老实说，我不完全理解?和!在Swift中的用法，如果是这导致了我的问题。删除！从变量中实现协议的方法会导致其他错误。

有人能帮个忙吗？

class ViewController: UIViewController, UIPageViewControllerDataSource {

var pageViewController : UIPageViewController?
var pageTitles = ["Over 200 Tips and Tricks", "Discover Hidden Features", "Bookmark Favorite Tip", "FreeRegular Update"]
var pageImages = ["page1.png", "page2.png", "page3.png", "page4.png"]
var currentIndex = 0

@IBAction func startWalkthrough(sender: UIButton) {
    var startingViewController : PageContentViewController = self.viewControllerAtIndex(0)!
    var viewControllers : NSArray = [startingViewController]
    self.pageViewController!.setViewControllers(viewControllers, direction: .Forward, animated: false, completion: nil)
}

override func viewDidLoad() {
    super.viewDidLoad()

    //Create page view controller
    self.pageViewController = UIPageViewController(transitionStyle: .Scroll, navigationOrientation: .Horizontal, options: nil)
    self.pageViewController!.dataSource = self

    let startingViewController : PageContentViewController = self.viewControllerAtIndex(0)!
    let viewControllers: NSArray = [startingViewController]
    self.pageViewController!.setViewControllers(viewControllers, direction: .Forward, animated: false, completion: nil)

    // Change the size of page view controller
    self.pageViewController!.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 30);

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

}

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

        var index = (viewController as PageContentViewController).pageIndex

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

        index!--

        println("Decreasing Index: \(index)")

        return self.viewControllerAtIndex(index!)
}

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

        var index = (viewController as PageContentViewController).pageIndex

        if index == NSNotFound {
            return nil
        }

        index!++

        println("Increasing Index: \(index)")

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

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

    if self.pageTitles.count == 0 || index >= self.pageTitles.count {
        return nil;
    }

    // Create a new view controller and pass suitable data.
    let pageContentViewController = self.storyboard!.instantiateViewControllerWithIdentifier("PageContentViewController") as PageContentViewController
    pageContentViewController.imageFile = self.pageImages[index]
    pageContentViewController.titleText = self.pageTitles[index]
    pageContentViewController.pageIndex = index

    return pageContentViewController;
}

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

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

Answer 1

这是因为UIPageViewControllerDataSource协议已经更新了方法签名-您正在使用：

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

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

但现在它们是：

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

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

当您对不符合规范的协议有疑问时，协议名称上的Command+Click将带您进入协议声明，您可以在其中查看是否正确地实现了它的接口