对于SWIFT4，我认为扩展UIViewController并创建一个可重用的确认控件是最优雅的方式。

你可以像下面这样扩展UIViewController:

extension UIViewController {

func AskConfirmation (title:String, message:String, completion:@escaping (_ result:Bool) -> Void) {
    let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
    self.present(alert, animated: true, completion: nil)

    alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: { action in
        completion(true)
    }))

    alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: { action in
        completion(false)
    }))
  }
}

那么你可以随时使用它:

 AskConfirmation(title: "YOUR MESSAGE TITLE", message: "YOUR MESSAGE") { (result) in
        if result { //User has clicked on Ok

        } else { //User has clicked on Cancel

        }
    }

在IOS 9上，你可以这样做

let alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Click", style: UIAlertActionStyle.default, handler: nil))
self.present(alert, animated: true, completion: nil)

通过Swift 2的协议扩展，你可以创建一个为视图控制器提供默认实现的协议:

ShowsAlert.swift

import UIKit

protocol ShowsAlert {}

extension ShowsAlert where Self: UIViewController {
    func showAlert(title: String = "Error", message: String) {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .Alert)
        alertController.addAction(UIAlertAction(title: "Ok", style: .Default, handler: nil))
        presentViewController(alertController, animated: true, completion: nil)
    }
}

ViewController.swift

class ViewController: UIViewController, ShowsAlert {
    override func viewDidLoad() {
        super.viewDidLoad()
        showAlert(message: "Hey there, I am an error message!")
    }
}

斯威夫特有一个有趣的例子:

private func presentRandomJoke() {
  if let randomJoke: String = jokesController.randomJoke() {
    let alertController: UIAlertController = UIAlertController(title:nil, message:randomJoke, preferredStyle: UIAlertControllerStyle.Alert)
    alertController.addAction(UIAlertAction(title:"Done", style:UIAlertActionStyle.Default, handler:nil))
    presentViewController(alertController, animated:true, completion:nil)
  }
}

SWIFT 4:简单地为UIViewController创建一个扩展，如下所示:

extension  UIViewController {        
    func showSuccessAlert(withTitle title: String, andMessage message:String) {
        let alert = UIAlertController(title: title, message: message,
                                  preferredStyle: UIAlertController.Style.alert)
        alert.addAction(UIAlertAction(title: "OK".localized, style:
        UIAlertAction.Style.default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}

现在在你的ViewController中，直接调用上面的函数，就好像它们是由UIViewController提供的一样。

    yourViewController.showSuccessAlert(withTitle: 
      "YourTitle", andMessage: "YourCustomTitle")

适用于13.0以上版本 使用SceneDelegate

适用于所有类型的课程

static func showWindowAlert(alertMessage: String, inVC:UIViewController) {
        DispatchQueue.main.async(execute: {
            guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
                let sceneDelegate = windowScene.delegate as? SceneDelegate
              else {
                return
              }
            sceneDelegate.window?.rootViewController = inVC
            sceneDelegate.window?.windowLevel = UIWindow.Level.alert + 1
        
            let alert2 = UIAlertController(title: App_Name, message: alertMessage, preferredStyle: .alert)
            let defaultAction2 = UIAlertAction(title: "OK", style: .default, handler: { action in
            })
            alert2.addAction(defaultAction2)
        
            sceneDelegate.window?.makeKeyAndVisible()
        
            sceneDelegate.window?.rootViewController?.present(alert2, animated: true, completion: nil)
        })
    }