场景:用户点击视图控制器上的按钮。视图控制器是导航堆栈中最顶层的(很明显)。tap调用在另一个类上调用的实用程序类方法。这里发生了不好的事情我想在控件返回到视图控制器之前在那里显示一个警告。

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

这是可能的UIAlertView(但可能不太合适)。

在这种情况下,你如何在myUtilityMethod中呈现UIAlertController ?


当前回答

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)
        }
    }
}

其他回答

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
    }
}

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)
}
extension UIApplication {
    /// The top most view controller
    static var topMostViewController: UIViewController? {
        return UIApplication.shared.keyWindow?.rootViewController?.visibleViewController
    }
}

extension UIViewController {
    /// The visible view controller from a given view controller
    var visibleViewController: UIViewController? {
        if let navigationController = self as? UINavigationController {
            return navigationController.topViewController?.visibleViewController
        } else if let tabBarController = self as? UITabBarController {
            return tabBarController.selectedViewController?.visibleViewController
        } else if let presentedViewController = presentedViewController {
            return presentedViewController.visibleViewController
        } else {
            return self
        }
    }
}

有了这个,你可以很容易地呈现你的警告,就像这样

UIApplication.topMostViewController?.present(viewController, animated: true, completion: nil)

需要注意的一件事是,如果有一个UIAlertController当前正在显示,UIApplication。topMostViewController将返回一个UIAlertController。在UIAlertController的顶部呈现有奇怪的行为,应该避免。因此,你应该手动检查!topMostViewController is UIAlertController),或者如果self是UIAlertController,添加一个else if case返回nil

extension UIViewController {
    /// The visible view controller from a given view controller
    var visibleViewController: UIViewController? {
        if let navigationController = self as? UINavigationController {
            return navigationController.topViewController?.visibleViewController
        } else if let tabBarController = self as? UITabBarController {
            return tabBarController.selectedViewController?.visibleViewController
        } else if let presentedViewController = presentedViewController {
            return presentedViewController.visibleViewController
        } else if self is UIAlertController {
            return nil
        } else {
            return self
        }
    }
}

我知道这是针对iOS的,因为搜索引擎中几乎所有的链接都能找到iOS的帖子,我想我应该把这个提供给macOS的开发者。

macOS上的Swift 5.5

根据Darkngs的回答,我在另一个类中添加了这个方法:

let alert = NSAlert()
let viewController = NSApplication.shared.keyWindow?.contentViewController
alert.messageText = "An Alert Message."
alert.addButton(withTitle: "Ok")
alert.beginSheetModal(for: (viewController?.view.window)!) {
    (returnCode: NSApplication.ModalResponse) -> Void in
}

更新到与iOS 13场景,打破了新的UIWindow方法。斯威夫特5.1。

fileprivate var alertWindows = [UIAlertController:UIWindow]()

extension UIAlertController {

    func presentInNewWindow(animated: Bool, completion: (() -> Void)?) {
        let foregroundActiveScene = UIApplication.shared.connectedScenes.filter { $0.activationState == .foregroundActive }.first
        guard let foregroundWindowScene = foregroundActiveScene as? UIWindowScene else { return }

        let window = UIWindow(windowScene: foregroundWindowScene)
        alertWindows[self] = window

        window.rootViewController = UIViewController()
        window.windowLevel = .alert + 1
        window.makeKeyAndVisible()
        window.rootViewController!.present( self, animated: animated, completion: completion)
    }

    open override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        alertWindows[self] = nil
    }

}