ios - NSNotification:尝试在其 View 不在窗口层次结构中的 ViewController 上显示 UIAlertController

Question

我正在尝试在通过 NSNotification 调用的函数中的 ViewController 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 UI 中的其他内容的完成 block (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)
}

有人知道为什么会这样吗？我不明白为什么它不在窗口层次结构中 - 它是从 self 显示的viewController 并在 VC 中的顶级函数中创建。

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 View Controller 不再是 Controller 层次结构的一部分，并且它的 View 不再位于任何窗口的 View 层次结构中时，就会发生这种情况。最有可能的是， Controller 被关闭或弹出，但它听到了通知并尝试显示警报 Controller 。

您应该更仔细地管理您的 Controller 状态。当 Controller 从您的 Controller 层次结构中被解雇或弹出时，可能会删除观察者。