其中一些答案只对我起了部分作用，将它们组合在AppDelegate中的以下类方法中是我的解决方案。它在iPad上工作，在UITabBarController视图中，在UINavigationController中，在呈现情态时。在iOS 10和13上进行测试。

+ (UIViewController *)rootViewController {
    UIViewController *rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
    if([rootViewController isKindOfClass:[UINavigationController class]])
        rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
    if([rootViewController isKindOfClass:[UITabBarController class]])
        rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
    if (rootViewController.presentedViewController != nil)
        rootViewController = rootViewController.presentedViewController;
    return rootViewController;
}

用法:

[[AppDelegate rootViewController] presentViewController ...

斯威夫特

let alertController = UIAlertController(title: "title", message: "message", preferredStyle: .alert)
//...
var rootViewController = UIApplication.shared.keyWindow?.rootViewController
if let navigationController = rootViewController as? UINavigationController {
    rootViewController = navigationController.viewControllers.first
}
if let tabBarController = rootViewController as? UITabBarController {
    rootViewController = tabBarController.selectedViewController
}
//...
rootViewController?.present(alertController, animated: true, completion: nil)

objective - c

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];
//...
id rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
if([rootViewController isKindOfClass:[UINavigationController class]])
{
    rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
}
if([rootViewController isKindOfClass:[UITabBarController class]])
{
    rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
}
//...
[rootViewController presentViewController:alertController animated:YES completion:nil];

创建扩展像在Aviel Gross回答。这里有Objective-C扩展。

这里有头文件*.h

//  UIAlertController+Showable.h

#import <UIKit/UIKit.h>

@interface UIAlertController (Showable)

- (void)show;

- (void)presentAnimated:(BOOL)animated
             completion:(void (^)(void))completion;

- (void)presentFromController:(UIViewController *)viewController
                     animated:(BOOL)animated
                   completion:(void (^)(void))completion;

@end

和实现:*.m

//  UIAlertController+Showable.m

#import "UIAlertController+Showable.h"

@implementation UIAlertController (Showable)

- (void)show
{
    [self presentAnimated:YES completion:nil];
}

- (void)presentAnimated:(BOOL)animated
             completion:(void (^)(void))completion
{
    UIViewController *rootVC = [UIApplication sharedApplication].keyWindow.rootViewController;
    if (rootVC != nil) {
        [self presentFromController:rootVC animated:animated completion:completion];
    }
}

- (void)presentFromController:(UIViewController *)viewController
                     animated:(BOOL)animated
                   completion:(void (^)(void))completion
{

    if ([viewController isKindOfClass:[UINavigationController class]]) {
        UIViewController *visibleVC = ((UINavigationController *)viewController).visibleViewController;
        [self presentFromController:visibleVC animated:animated completion:completion];
    } else if ([viewController isKindOfClass:[UITabBarController class]]) {
        UIViewController *selectedVC = ((UITabBarController *)viewController).selectedViewController;
        [self presentFromController:selectedVC animated:animated completion:completion];
    } else {
        [viewController presentViewController:self animated:animated completion:completion];
    }
}

@end

你在你的实现文件中使用这个扩展，就像这样:

#import "UIAlertController+Showable.h"

UIAlertController* alert = [UIAlertController
    alertControllerWithTitle:@"Title here"
                     message:@"Detail message here"
              preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction* defaultAction = [UIAlertAction
    actionWithTitle:@"OK"
              style:UIAlertActionStyleDefault
            handler:^(UIAlertAction * action) {}];
[alert addAction:defaultAction];

// Add more actions if needed

[alert show];

Kevin Sliech提供了一个很好的解决方案。

我现在在我的主UIViewController子类中使用下面的代码。

我做的一个小改动是检查最好的表示控制器是不是一个普通的UIViewController。如果不是，那就一定是某个VC表示一个普通VC。因此，我们返回正在呈现的VC。

- (UIViewController *)bestPresentationController
{
    UIViewController *bestPresentationController = [UIApplication sharedApplication].keyWindow.rootViewController;

    if (![bestPresentationController isMemberOfClass:[UIViewController class]])
    {
        bestPresentationController = bestPresentationController.presentedViewController;
    }    

    return bestPresentationController;
}

在我的测试中似乎一切正常。

谢谢你，凯文!

交叉张贴我的答案，因为这两个线程没有被标记为欺骗…

现在UIViewController是responder chain的一部分，你可以这样做:

if let vc = self.nextResponder()?.targetForAction(#selector(UIViewController.presentViewController(_:animated:completion:)), withSender: self) as? UIViewController {

    let alert = UIAlertController(title: "A snappy title", message: "Something bad happened", preferredStyle: .Alert)
    alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))

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

我尝试了上面提到的所有方法，但都没有成功。我在Swift 3.0中使用的方法:

extension UIAlertController {
    func show() {
        present(animated: true, completion: nil)
    }

    func present(animated: Bool, completion: (() -> Void)?) {
        if var topController = UIApplication.shared.keyWindow?.rootViewController {
            while let presentedViewController = topController.presentedViewController {
                topController = presentedViewController
            }
            topController.present(self, animated: animated, completion: completion)
        }
    }
}