AlertController 不在 window 层次结构中

Question

我刚刚使用 ViewController class 创建了一个单视图应用程序项目。我想从位于我自己的 class 中的函数显示一个 UIAlertController。

这是我的 class 警报。

class AlertController: UIViewController {
     func showAlert() { 
         var alert = UIAlertController(title: "abc", message: "def", preferredStyle: .Alert)
         self.presentViewController(alert, animated: true, completion: nil)
     }
}

这是执行警报的 ViewController。

class ViewController: UIViewController {
   override func viewDidLoad() {
       super.viewDidLoad()  
   }

   @IBAction func showAlertButton(sender: AnyObject) {
       var alert = AlertController()
       alert.showAlert()
   }
}

这是我得到的，而不是漂亮的警报。

警告：尝试在 Sprint1.AlertController 上呈现 UIAlertController：0x797d2d20：0x797cc500，其视图不在 window 层次结构中！

我该怎么办？

Answer 1

让我们看看您的视图层次结构。你有一个ViewController。然后你正在创建一个 AlertController，你没有将它添加到你的层次结构中，而是在它上面调用一个实例方法，它试图使用 AlertController 作为呈现控制器来显示另一个控制器（UIAlertController).

+ ViewController
    + AlertController (not in hierarchy)
        + UIAlertController (cannot be presented from AlertController)

简化您的代码

class ViewController: UIViewController {
   override func viewDidLoad() {
       super.viewDidLoad()  
   }

   @IBAction func showAlertButton(sender: AnyObject) {
       var alert = UIAlertController(title: "abc", message: "def", preferredStyle: .Alert)
       self.presentViewController(alert, animated: true, completion: nil)
   }
}

这会起作用。

如果您需要 AlertController 的东西，您必须先将它添加到层次结构中，例如使用 addChildViewController 或使用另一个 presentViewController 调用。

如果您希望 class 只是创建警报的助手，它应该如下所示：

class AlertHelper {
    func showAlert(fromController controller: UIViewController) { 
        var alert = UIAlertController(title: "abc", message: "def", preferredStyle: .Alert)
        controller.presentViewController(alert, animated: true, completion: nil)
    }
}

称为

 var alert = AlertHelper()
 alert.showAlert(fromController: self)

Answer 2

如果你想创建一个单独的 class 来显示这样的警报，subclass NSObject 而不是 UIViewController。

并将启动它的 ViewControllers 引用传递给 showAlert 函数，以便您可以在那里显示警报视图。

Answer 3

写下面3行，我们要做的就是这个

Swift 3.0

private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
     UIApplication.shared.keyWindow?.rootViewController?.present(alert, animated: flag, completion: completion)
  }

Swift 2.0

  private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
     UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alert, animated: flag, completion: completion)
  }

Answer 4

如果您从模态控制器实例化您的 UIAlertController，您需要在 viewDidAppear 中执行，而不是在 viewDidLoad 中执行，否则您会收到错误消息。

这是我的代码 (Swift 4):

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    let alertController = UIAlertController(title: "Foo", message: "Bar", preferredStyle: .alert)

    alertController.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
    present(alertController, animated: true, completion: nil)
}

Answer 5

这是 Swift3 中 Utility.swift class（不是 UIViewController）中 UIAlertController 的代码，谢谢 Mitsuaki！

private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
    UIApplication.shared.keyWindow?.rootViewController?.present(alert, animated: flag, completion: completion)
}
func warningAlert(title: String, message: String ){
    let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler:  { (action) -> Void in
    }))        
 //   self.present(alert, animated: true, completion: nil)
    presentViewController(alert: alert, animated: true, completion: nil)
}

Answer 6

您可以使用以下函数从任何地方调用警报，只需在 AnyClass 中包含这些方法

class func topMostController() -> UIViewController {
        var topController: UIViewController? = UIApplication.shared.keyWindow?.rootViewController
        while ((topController?.presentedViewController) != nil) {
            topController = topController?.presentedViewController
        }
        return topController!
    }

    class func alert(message:String){
        let alert=UIAlertController(title: "AppName", message: message, preferredStyle: .alert);
        let cancelAction: UIAlertAction = UIAlertAction(title: "OK", style: .cancel) { action -> Void in

        }
        alert.addAction(cancelAction)
        AnyClass.topMostController().present(alert, animated: true, completion: nil);
    }

然后调用

AnyClass.alert(message:"Your Message")

Answer 7

它帮助我在 viewDidLoad 方法和触发 alert 方法之间稍作延迟：

   [self performSelector:@selector(checkPhotoPermission) withObject:nil afterDelay:0.1f];

Answer 8

这对我有用：

- (UIViewController *)topViewController{
  return [self topViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

- (UIViewController *)topViewController:(UIViewController *)rootViewController
{
  if (rootViewController.presentedViewController == nil) {
    return rootViewController;
  }

  if ([rootViewController.presentedViewController isMemberOfClass:[UINavigationController class]]) {
    UINavigationController *navigationController = (UINavigationController *)rootViewController.presentedViewController;
    UIViewController *lastViewController = [[navigationController viewControllers] lastObject];
    return [self topViewController:lastViewController];
  }

  UIViewController *presentedViewController = (UIViewController *)rootViewController.presentedViewController;
  return [self topViewController:presentedViewController];
}

实施：

UIViewController * topViewController = [self topViewController];

与警报一起使用：

[topViewController presentViewController:yourAlert animated:YES completion:nil];

您可以从应用中的任何 class 发送提醒（使用 UIKit：#import <UIKit/UIKit.h>）

Source here.

Answer 9

// I always find it helpful when you want to alert from anywhere it's codebase 
// if you find the error above mentioned in the question' title.

let controller = UIAlertController(title: "", message: "Alert!", preferredStyle: UIAlertController.Style.alert)
    
let action = UIAlertAction(title: "Cancel"   , style: UIAlertAction.Style.cancel, handler: nil)
controller.addAction(action)

// Find Root View Controller
var rootVC = UIApplication.shared.windows.first?.rootViewController

if var topController = rootVC {
    while let presentedViewController = topController.presentedViewController {
        topController = presentedViewController
    }
    rootVC = topController
}
rootVC?.present(controller, animated: true, completion: nil)

AlertController 不在 window 层次结构中

AlertController is not in the window hierarchy

storyboard

uialertview

ios

swift

uialertcontroller