Question

在我的快捷应用程序中，我需要知道应用程序从哪个屏幕进入后台。我试图以这种方式使用NotificationCenter：

class MainViewController: UIViewController{
   override func viewDidLoad() {
        super.viewDidLoad()
        let notificationCenter = NotificationCenter.default
        notificationCenter.addObserver(self, selector: #selector(appMovedToBackgroundMain), name: UIApplication.didEnterBackgroundNotification, object: nil)
    }

    @objc func appMovedToBackgroundMain() {
        print("main - App moved to Background!")
    }
}

class InitViewController: UIViewController{
       override func viewDidLoad() {
            super.viewDidLoad()
            let notificationCenter = NotificationCenter.default
            notificationCenter.addObserver(self, selector: #selector(appMovedToBackgroundInit), name: UIApplication.didEnterBackgroundNotification, object: nil)
        }

        @objc func appMovedToBackgroundInit() {
            print("init - App moved to Background!")
        }
    }

当我在Home按下MainViewController按钮时，我进入了Xcode的控制台，这些行如下：

init - App moved to Background!
main - App moved to Background!

，我希望那里只有一行-main - App moved to Background!。我怎样才能做到这一点？

Answer 1

您可以使用以下功能：

 func applicationWillEnterForeground(_ application: UIApplication) {
    // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}

您可以在此处检查哪个控制器位于导航控制器的控制器顶部。

print(self.navigationController.topViewController)

Answer 2

在AppDelegate的方法：applicationDidEnterBackground或applicationWillEnterForeground，你可以得到最顶端的UIViewController。据在这个问题上很好地解释：Get top most UIViewController

Answer 3

当应用程序进入后台状态时，将调用以下方法。

func applicationWillEnterForeground(_ application: UIApplication) {
    // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}

swift-如何检测从哪个ViewController应用程序进入后台？

3 个答案: