警告:尝试在视图不在窗口层次结构中的<x.x:x>上显示

Question

我是Swift的新手，但我正在创建一个应用程序，需要在一定时间后输入Touch-ID或PIN。我正在检查来自AppDelegate.swift的计时器，看看它是否已经过期，如果它已经过期，我将调用我的"BaseTableViewController“，它包含我的函数authenticateUser。我再一次从我的AppDelegate.swift文件中调用它，方法是创建一个BaseTableViewController var baseTableVC = BaseTableViewController()的实例，并在计时器过期时调用self.baseTableVC.authenticateUser()。

无论如何，我得到了:警告：Attempt to present <UIAlertController: 0x7fed5ae1dcf0> on <admin.BaseViewController: 0x7fed5ad279d0> whose view is not in the window hierarchy!

提前感谢您的帮助！

    func showPasswordAlert(){
    let alertController = UIAlertController(title: "Touch ID Password", message: "Please enter your password", preferredStyle: .Alert)
    let defaultAction = UIAlertAction(title: "OK", style: .Cancel) {(action) -> Void in
        if let textField = alertController.textFields?.first as UITextField?{
            if textField.text == "hello" {
                print("Authentication successfull!")
            }
            else{
                self.showPasswordAlert()
            }
        }

    }
    alertController.addAction(defaultAction)
    alertController.addTextFieldWithConfigurationHandler{(textField) -> Void in
        textField.placeholder = "Password"
        textField.secureTextEntry = true

    }
    presentViewController(alertController, animated: true, completion: nil)

}

func authenticateUser(){
    let context = LAContext()
    var error: NSError?
    let reasonString = "Authentication is required for Admin!"
    context.localizedFallbackTitle = "Enter your PIN Code"

    if context.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error: &error){
        context.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: reasonString, reply: {(success, policyError) ->Void in
            if success{
                print("Authentication successful!")
            }
            else{
                switch policyError!.code{
                case LAError.SystemCancel.rawValue:
                    print("Authentication was cancelled by the system!")
                case LAError.UserCancel.rawValue:
                    NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in
                        self.showPasswordAlert()

                    })
                    print("Authentication was cancelled by the user!")
                case LAError.UserFallback.rawValue:
                    print("User selected to enter password.")
                    NSOperationQueue.mainQueue().addOperationWithBlock({() -> Void in
                        self.showPasswordAlert()
                    })
                default:
                    print("Authentication failed!")
                    NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in
                        self.showPasswordAlert()
                    })
                }
            }
        })
    }
    else{
        print(error?.localizedDescription)
        NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in
            self.showPasswordAlert()
        })
    }

var baseTableVC = BaseTableViewController()

func applicationWillEnterForeground(application: UIApplication) {
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
    let logInStatus = NSUserDefaults.standardUserDefaults()
    let currentTime = NSDate().timeIntervalSince1970
    let roundCurrentTime = (round(currentTime))
    // Pin expire limit
    let pinExpLimit: Double = 30
    // Set the exact time of expire for pin
    let pinExpDate = (currentTime + pinExpLimit)
    let newPinExpDate = (round(pinExpDate))
    if (logInStatus.doubleForKey("expPinTime") <= roundCurrentTime) {
        self.baseTableVC.authenticateUser()
        print("AppDelegate Pin Exp Time")
        print(logInStatus.doubleForKey("expPinTime"))
        //print(newPinExpDate)
        print("AppDelegate Current Time")
        print(roundCurrentTime)
        logInStatus.setDouble(newPinExpDate, forKey: "expPinTime")
        NSUserDefaults.standardUserDefaults().synchronize()

    }
}

Answer 1

我怀疑您只是创建了BaseTableViewController的一个实例，但是在呈现UIAlertController的实例之前，您没有将它的视图添加到视图层次结构中。

如果self.baseTableVC是应用程序的根视图控制器，那么像这样的调用

baseTableVC.presentViewController(instanceOfUIAlertController, animated: true, completion: yourCompletionBlock)

应该从AppDelegate内部工作。如果self.baseTableVC不是根视图控制器，请确保在应用的根VC上调用前面的命令

window.rootViewController.presentViewController(instanceOfUIAlertController, animated: true, completion: yourCompletionBlock)

或者确保在视图层次结构中嵌入self.baseTableVC的视图，然后调用

baseTableVC.presentViewController(instanceOfUIAlertController, animated: true, completion: yourCompletionBlock)

顺便说一句，如果你的提醒必须在应用程序中的任何地方显示，那么你的方法是可以的。相反，如果您的警报必须仅从特定屏幕显示，我将从应用程序委托中删除计时器逻辑，并将其移动到呈现视图控制器中。这将使您的应用程序委托远离不必要的代码，并将控制逻辑限制在正确的位置:呈现视图控制器

Answer 2

你不能仅仅通过调用默认的构造函数来创建视图控制器的实例，使用故事板。如果我错了，请纠正我