Swift dynamic cast failed UIPageViewController

问题

I am trying to cast my window.rootViewController as a UIPageViewController but anytime I access the class property which I defined it blows up with swift dynamic cast failed. My storyboard has a UIPageViewController is the initial scene.

PageViewController is just a subclass of UIPageViewController

class AppDelegate: UIResponder, UIApplicationDelegate, UIPageViewControllerDataSource {

    var window: UIWindow!

    var pageViewController: PageViewController {
        return window.rootViewController as PageViewController
    }

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool {

        pageViewController.dataSource = self

        return true
    }

 }

回答1:

The main issue actually was because I was subclassing UIPageViewController I had to add the custom class to the ViewController inside my storyboard. At first I figured that since PageViewController is a UIPageViewController, and I am just casting the rootViewController to a PageViewController, it should've of worked. By adding the custom class it fixed my problem.

I also tested by not subclassing, it worked with out specifying a custom class.

来源：https://stackoverflow.com/questions/24327267/swift-dynamic-cast-failed-uipageviewcontroller