NSNotification：尝试在视图不在 window 层次结构中的 ViewController 上呈现 UIAlertController

Question

我试图在我的 ViewController 中通过 NSNotification 调用的函数中显示 UIAlertController。但是我收到错误：

Attempt to present <UIAlertController: 0x7fe013d05d40> on <submarine.ViewController: 0x7fe011f20370> whose view is not in the window hierarchy!

NSNotification 是从我的 UI 中的其他内容的完成块（我猜是回调）发布的。因为它是一个回调，所以无法显示。因此我想我会尝试 NSNotificationCentre 来解决这个问题而不使用 rootViewController 来显示警报。

我的代码是：

override func viewDidAppear(animated: Bool) {
    // Handle onboarding
    if needsOnboarding() {
        handleOnboarding() // This create the completion block that posts the NSNotification
    }

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "showTermsAlert:", name:"showTermsAlert", object: nil)
}

func showTermsAlert(notification: NSNotification) {
    let termsAlert:UIAlertController = UIAlertController(title: "Terms And Conditions", message: "Please view the terms below before accepting them.", preferredStyle: UIAlertControllerStyle.Alert)

    termsAlert.addAction(UIAlertAction(title: "View Terms", style: .Default, handler: { (action: UIAlertAction!) in
        UIApplication.sharedApplication().openURL(NSURL(string: "my_terms_url")!)
    }))

    termsAlert.addAction(UIAlertAction(title: "I Agree to the Terms", style: .Default, handler: { (action: UIAlertAction!) in
        self.onboardingFinished()
    }))

    self.presentViewController(termsAlert, animated: true, completion: nil)
}

有没有人知道为什么会这样？我不明白为什么它不在 window 层次结构中 - 它是从 self viewController 中呈现的，并且是在 VC 中的顶级函数中创建的。

谢谢！

编辑：handleOnboarding():

中的原始代码

使用的库：Onboard

func handleOnboarding() {

        let secondPage = OnboardingContentViewController(title: "What's going on?", body: "Submarine routes your data through our network, around any filters and restrictions, giving you unrestricted and unmonitored internet access.", image: UIImage(named: "back"), buttonText: "Next") { () -> Void in
            // do something here when users press the button, like ask for location services permissions, register for push notifications, connect to social media, or finish the onboarding process
        }
        secondPage.movesToNextViewController = true

        let thirdPage = OnboardingContentViewController(title: "Terms of Use", body: "You must agree to our Terms of Use to use Submarine.\nIf you don't, please close Submarine.", image: UIImage(named: "back"), buttonText: "View Terms") { () -> Void in

            let termsAlert:UIAlertController = UIAlertController(title: "Terms And Conditions", message: "Please view the terms below before accepting them.", preferredStyle: UIAlertControllerStyle.Alert)

            termsAlert.addAction(UIAlertAction(title: "View Terms", style: .Default, handler: { (action: UIAlertAction!) in
                UIApplication.sharedApplication().openURL(NSURL(string: "my_policy_url")!)
            }))

            termsAlert.addAction(UIAlertAction(title: "I Agree to the Terms", style: .Default, handler: { (action: UIAlertAction!) in
                self.onboardingFinished()
            }))

            self.presentViewController(termsAlert, animated: true, completion: nil)

//            NSNotificationCenter.defaultCenter().postNotificationName("showTermsAlert", object: nil)
        }

        // Image
        let onboardingVC = OnboardingViewController(backgroundImage: UIImage(named: "back"), contents: [secondPage, thirdPage])

        self.navigationController?.presentViewController(onboardingVC, animated: false, completion: nil)

    }

Answer 1

当呈现视图控制器不再是控制器层次结构的一部分，并且它的视图不再位于任何 window 的视图层次结构中时，就会发生这种情况。最有可能的是，控制器被关闭或弹出，但它听到了通知并尝试显示警报控制器。

您应该更仔细地管理您的控制器状态。当控制器从您的控制器层次结构中被解雇或弹出时，可能会删除观察者。

Answer 2

我想对您的代码进行一些更改。在 viewDidAppear: 中添加对 super 的调用，并停止使用 NSNotification 进行演示。您不知道使用此模式将调用哪个线程 showTermsAlert。您可以通过直接调用 showTermsAlert 使您的意图更加明确，这也将保证您在主线程上。

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    // Handle onboarding
    if needsOnboarding() {
        self.showTermsAlert()
    }
}

func showTermsAlert() {
    let termsAlert:UIAlertController = UIAlertController(title: "Terms And Conditions", message: "Please view the terms below before accepting them.", preferredStyle: UIAlertControllerStyle.Alert)

    termsAlert.addAction(UIAlertAction(title: "View Terms", style: .Default, handler: { (action: UIAlertAction!) in
    UIApplication.sharedApplication().openURL(NSURL(string: "my_terms_url")!)
}))

    termsAlert.addAction(UIAlertAction(title: "I Agree to the Terms", style: .Default, handler: { (action: UIAlertAction!) in
    self.onboardingFinished()
}))

    self.presentViewController(termsAlert, animated: true, completion: nil)
}

NSNotification：尝试在视图不在 window 层次结构中的 ViewController 上呈现 UIAlertController

NSNotification: Attempt to present UIAlertController on ViewController whose view is not in the window hierarchy

uiviewcontroller

nsnotification

ios

swift

uialertcontroller