检测哪个屏幕用户退出了应用

Question

I haven't been able to find anything on this so far, so if you could either guide or point me in the direction of where I can figure this out I would greatly appreciate it.

I was wondering if we can detect from what view controller a user either quit, or exited the app (through the home button or maybe even a phone call came in etc...). I am working on a game where users ask one another multiple questions at a time and I want to make sure that if a user views the first question, answers incorrectly and quits the app before answering the second question, he/ she cannot access the first question again on app reboot. I would like it to be so that the user gets 0 points in the case the app is quit while on this view controller.

Answer 1

It should be simple to track this yourself by sending a notification during each viewDidAppear of each of your view controllers. Have something, say, in your AppDelegate (a singleton would be better), listen and update some persistent state regarding last view controller viewed.

Answer 2

Add this extension:

extension UIApplication {
    class func topViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let nav = base as? UINavigationController {
            return topViewController(base: nav.visibleViewController)
        }
        if let tab = base as? UITabBarController {
            if let selected = tab.selectedViewController {
                return topViewController(base: selected)
            }
        }
        if let presented = base?.presentedViewController {
            return topViewController(base: presented)
        }
        return base
    }
}

And then from you AppDelegates applicationDidEnterBackground call it:

func applicationDidEnterBackground(_ application: UIApplication) {
    if let viewController = UIApplication.topViewController() {
        print(viewController)
    }
}

Will print out:

<TestApp.MenuController: 0x7ff2bb501940>