从另一个类调用警报视图，但是不在一个层次结构中

Question

我试图从视图控制器中的一个类调用函数：

var rate = RateMyApp.sharedInstance 
rate.showRatingAlert()

在RateMyApp类中，我称为警报视图：

 var window: AnyObject = UIApplication.sharedApplication().keyWindow!;
        var vc = window.rootViewController;
      vc?!.presentViewController(alert, animated: true, completion: nil)

但是，没有显示警报，并且有一种警告：

 Warning: Attempt to present <UIAlertController: 0x15fe3dcf0> on <drawtext.ViewController: 0x16002a800> whose view is not in the window hierarchy!

有时会发生这种情况，如果一个人隐藏了该应用程序，然后再次打开它几次，则有时会显示警报。

什么会导致这种奇怪的行为？

Answer 1

似乎要解决：

     var window = UIApplication.sharedApplication().keyWindow!
           // var vc = window.rootViewController!!.presentingViewController

        var vc = window.rootViewController;
        while (vc!.presentedViewController != nil)
        {
            vc = vc!.presentedViewController;
        }

      vc?.presentViewController(alert, animated: true, completion: nil)

看起来像车丹的解决方案

Answer 2

使用UIAlertController时，应从视图层次结构中最顶层的ViewController呈现它。

所以我建议：

var rate = RateMyApp.sharedInstance 
rate.showRatingAlert(self)

在RateMyApp类中：

func showRatingAlert(sender:UIViewController){
//..... your UIAlertController here
 sender.presentViewController(alert, animated: true, completion: nil)
}

更一般的说，func presentViewController(:_)只能从最顶部的View Controller调用。

您可以像这样创建扩展名：

extension UIViewController {
  @warn_unused_result
  static func topViewController(base: UIViewController? = UIApplication.sharedApplication().windows.first?.rootViewController) -> UIViewController? {

    if let nav = base as? UINavigationController {
        return topViewController(nav.visibleViewController)
    }

    if let tab = base as? UITabBarController {
        let moreNavigationController = tab.moreNavigationController

        if let top = moreNavigationController.topViewController where top.view.window != nil {
            return topViewController(top)
        } else if let selected = tab.selectedViewController {
            return topViewController(selected)
        }
    }

    if let presented = base?.presentedViewController {
        return topViewController(presented)
    }

    if let splitVC = base as? UISplitViewController {
        if let lastVC = splitVC.viewControllers.last {
            return topViewController(lastVC)
        }
        else {
            return splitVC
        }
    }

    if let lastChildVC = base?.childViewControllers.last {
        return topViewController(lastChildVC)
    }

    return base
   }
}

您可以按以下方式调用警报：

func showRatingAlert() {
   if let vc = UIViewController.topViewController() {
      vc.presentViewController(alert, animated: true, completion: nil)
   }
}

Answer 3

窗户向上时做

dispatch_async(dispatch_get_main_queue(), {
    var window: AnyObject = UIApplication.sharedApplication().keyWindow!;
    var vc = window.rootViewController;
    vc?!.presentViewController(alert, animated: true, completion: nil)
})

Answer 4

按照我的想法，您只需要

1. 获取最高的ViewController [当前显示]

2. 呈现您的警报。

获取最高视图控制器

[这是obj C代码。 请尽快转换]

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

-(UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController {
    if ([rootViewController isKindOfClass:[UITabBarController class]]) {
        UITabBarController* tabBarController = (UITabBarController*)rootViewController;
        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController* navigationController = (UINavigationController*)rootViewController;
        return [self topViewControllerWithRootViewController:navigationController.visibleViewController];
    } else if (rootViewController.presentedViewController) {
        UIViewController* presentedViewController = rootViewController.presentedViewController;
        return [self topViewControllerWithRootViewController:presentedViewController];
    } else {
        return rootViewController;
    }
}

然后

UIViewController * topController = [self topViewController];

现在在topController上显示您的警报。

抱歉，我无法为您提供Swift代码。 但是希望这足以暗示。