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)
        }
    }
}

你可以将当前视图或控制器作为参数发送:

+ (void)myUtilityMethod:(id)controller {
    // do stuff
    // something bad happened, display an alert.
}

斯威夫特5

在显示消息后隐藏窗口是很重要的。

func showErrorMessage(_ message: String) {
    let alertWindow = UIWindow(frame: UIScreen.main.bounds)
    alertWindow.rootViewController = UIViewController()

    let alertController = UIAlertController(title: "Error", message: message, preferredStyle: UIAlertController.Style.alert)
    alertController.addAction(UIAlertAction(title: "Close", style: UIAlertAction.Style.cancel, handler: { _ in
        alertWindow.isHidden = true
    }))
    
    alertWindow.windowLevel = UIWindow.Level.alert + 1;
    alertWindow.makeKeyAndVisible()
    alertWindow.rootViewController?.present(alertController, animated: true, completion: nil)
}

几个月前我发过一个类似的问题，我想我终于解决了这个问题。如果你只是想看代码，请点击我文章底部的链接。

解决方案是使用一个额外的UIWindow。

当你想要显示你的UIAlertController:

使你的窗口成为键和可见窗口(window. makekeyandvisible ()) 只需使用一个普通的UIViewController实例作为新窗口的rootViewController。(窗口。rootViewController = UIViewController()) 在你窗口的rootViewController上显示你的UIAlertController

有几点需要注意:

你的UIWindow必须是强引用的。如果它没有被强引用，它将永远不会出现(因为它已经被释放了)。我建议使用属性，但我也成功地使用了关联对象。 为了确保窗口显示在其他所有内容之上(包括系统UIAlertControllers)，我设置了windowLevel。(窗口。windowLevel = UIWindowLevelAlert + 1)

最后，我有一个完整的实现，如果你只是想看看。

https://github.com/dbettermann/DBAlertController

如果有人感兴趣，我创建了一个Swift 3版本的@agilityvision答案。代码:

import Foundation
import UIKit

extension UIAlertController {

    var window: UIWindow? {
        get {
            return objc_getAssociatedObject(self, "window") as? UIWindow
        }
        set {
            objc_setAssociatedObject(self, "window", newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

    open override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        self.window?.isHidden = true
        self.window = nil
    }

    func show(animated: Bool = true) {
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = UIViewController(nibName: nil, bundle: nil)

        let delegate = UIApplication.shared.delegate
        if delegate?.window != nil {
            window.tintColor = delegate!.window!!.tintColor
        }

        window.windowLevel = UIApplication.shared.windows.last!.windowLevel + 1

        window.makeKeyAndVisible()
        window.rootViewController!.present(self, animated: animated, completion: nil)

        self.window = window
    }
}

除了给出的很好的答案(agilityvision, adib, malhal)。为了达到像以前的UIAlertViews那样的排队行为(避免警报窗口重叠)，使用这个块来观察窗口级别的可用性:

@interface UIWindow (WLWindowLevel)

+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block;

@end

@implementation UIWindow (WLWindowLevel)

+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block {
    UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;
    if (keyWindow.windowLevel == level) {
        // window level is occupied, listen for windows to hide
        id observer;
        observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIWindowDidBecomeHiddenNotification object:keyWindow queue:nil usingBlock:^(NSNotification *note) {
            [[NSNotificationCenter defaultCenter] removeObserver:observer];
            [self notifyWindowLevelIsAvailable:level withBlock:block]; // recursive retry
        }];

    } else {
        block(); // window level is available
    }
}

@end

完整的例子:

[UIWindow notifyWindowLevelIsAvailable:UIWindowLevelAlert withBlock:^{
    UIWindow *alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    alertWindow.windowLevel = UIWindowLevelAlert;
    alertWindow.rootViewController = [UIViewController new];
    [alertWindow makeKeyAndVisible];

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Alert" message:nil preferredStyle:UIAlertControllerStyleAlert];
    [alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        alertWindow.hidden = YES;
    }]];

    [alertWindow.rootViewController presentViewController:alertController animated:YES completion:nil];
}];

这将允许您避免警报窗口重叠。同样的方法可以用于为任意数量的窗口层分离和放入队列视图控制器。