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

@agilityvision的回答非常好。我有在swift项目中使用的感觉,所以我想我将分享我使用swift 3.0的答案

fileprivate class MyUIAlertController: UIAlertController {

  typealias Handler = () -> Void

  struct AssociatedKeys {
    static var alertWindowKey = "alertWindowKey"
  }

  dynamic var _alertWindow: UIWindow?

  var alertWindow: UIWindow? {
    return objc_getAssociatedObject(self, &AssociatedKeys.alertWindowKey) as? UIWindow
  }


  func setAlert(inWindow window: UIWindow) {
    objc_setAssociatedObject(self, &AssociatedKeys.alertWindowKey, _alertWindow, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
  }

  func show(completion: Handler? = nil) {
    show(animated: true, completion: completion)
  }

  func show(animated: Bool, completion: Handler? =  nil) {
    _alertWindow = UIWindow(frame: UIScreen.main.bounds)
    _alertWindow?.rootViewController = UIViewController()

    if let delegate: UIApplicationDelegate = UIApplication.shared.delegate, let window = delegate.window {
      _alertWindow?.tintColor = window?.tintColor

    }

    let topWindow = UIApplication.shared.windows.last
    _alertWindow?.windowLevel = topWindow?.windowLevel ?? 0 + 1
    _alertWindow?.makeKeyAndVisible()
    _alertWindow?.rootViewController?.present(self, animated: animated, completion: completion)
  }

  fileprivate override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    _alertWindow?.isHidden = true
    _alertWindow = nil
  }
}

其他回答

创建helper类AlertWindow并使用as

let alertWindow = AlertWindow();
let alert = UIAlertController(title: "Hello", message: "message", preferredStyle: .alert);
let cancel = UIAlertAction(title: "Ok", style: .cancel){(action) in

    //....  action code here

    // reference to alertWindow retain it. Every action must have this at end

    alertWindow.isHidden = true;

   //  here AlertWindow.deinit{  }

}
alert.addAction(cancel);
alertWindow.present(alert, animated: true, completion: nil)


class AlertWindow:UIWindow{

    convenience init(){
        self.init(frame:UIScreen.main.bounds);
    }

    override init(frame: CGRect) {
        super.init(frame: frame);
        if let color = UIApplication.shared.delegate?.window??.tintColor {
            tintColor = color;
        }
        rootViewController = UIViewController()
        windowLevel = UIWindowLevelAlert + 1;
        makeKeyAndVisible()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    deinit{
        //  semaphor.signal();
    }

    func present(_ ctrl:UIViewController, animated:Bool, completion: (()->Void)?){
        rootViewController!.present(ctrl, animated: animated, completion: completion);
    }
}

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
    }
}
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
        }
    }
}

Swift 4+ / iOS 13:

基于https://stackoverflow.com/a/47797463/7493938,它使用了iOS 13已弃用的。keywindow方法。

extension UIAlertController {
  func show(animated: Bool = true, completion: (() -> Void)? = nil) {
    if let visibleViewController = UIApplication.shared.windows.filter({$0.isKeyWindow}).first?.visibleViewController {
      visibleViewController.present(self, animated: animated, completion: completion)
    }
  }
}

(我无法编辑原始答案,因为编辑队列已满。

iOS13场景支持(当使用UIWindowScene时)

import UIKit

private var windows: [String:UIWindow] = [:]

extension UIWindowScene {
    static var focused: UIWindowScene? {
        return UIApplication.shared.connectedScenes
            .first { $0.activationState == .foregroundActive && $0 is UIWindowScene } as? UIWindowScene
    }
}

class StyledAlertController: UIAlertController {

    var wid: String?

    func present(animated: Bool, completion: (() -> Void)?) {

        //let window = UIWindow(frame: UIScreen.main.bounds)
        guard let window = UIWindowScene.focused.map(UIWindow.init(windowScene:)) else {
            return
        }
        window.rootViewController = UIViewController()
        window.windowLevel = .alert + 1
        window.makeKeyAndVisible()
        window.rootViewController!.present(self, animated: animated, completion: completion)

        wid = UUID().uuidString
        windows[wid!] = window
    }

    open override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        if let wid = wid {
            windows[wid] = nil
        }

    }

}