// UIAlertView is deprecated. Use UIAlertController 
  // title = title of the alert view.
  // message = Alert message you want to show.
  // By tap on "OK" , Alert view will dismiss.

 UIAlertView(title: "Alert", message: "Enter Message here.", delegate: nil, cancelButtonTitle: "OK").show()

iOS 13 Xcode 11+ Swift 5。X

UIAlertController现在可以提供警报以及动作表

警报

// First instantiate the UIAlertController

let alert = UIAlertController(title: "Title",
                              message: "Message ?",
                              preferredStyle: .alert)


 // Add action buttons to it and attach handler functions if you want to 

 alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
 alert.addAction(UIAlertAction(title: "Just Do It!", style: .destructive, handler: nil))
 alert.addAction(UIAlertAction(title: "Maybe", style: .default, handler: nil))

// Show the alert by presenting it

self.present(alert, animated: true)

请注意，当点击警报视图时，所有操作按钮的基本属性都是关闭警报视图。style参数只是用来决定文本的颜色(以及按钮应该出现的默认顺序，这些ofc可以改变)

示例处理程序函数可以是

func handler(_ action: UIAlertAction) { 

   if action.title == 'Title' {
       // do stuff
   }

}

作为旁注，我想说的是，与其创建3个不同的处理程序，你可以只创建1个处理程序，并以上面所示的方式跟踪到引发它的元素 我们也可以检查警报。我们可以有多个。default样式的动作，我不建议这样做

动作表

解释是类似的，因为这里的主要区别是提醒会打断用户，而在iPhone中，操作表从底部滑动，在iPad中以弹出窗口的形式出现

操作表的目的是指导用户根据当前状态决定操作。所以你必须像对待十字路口一样对待动作表单!通常没有消息，标题呈现为标题大小的文本

let action = UIAlertController(title: "What do you want to do with the message",
                               message: nil,
                               preferredStyle: .actionSheet)

action.addAction(UIAlertAction(title: "Cancel", style: .cancel)) 

for act in ["Save", "Post", "Discard"] {  
          action.addAction(UIAlertAction(title: act, style: .default, handler: nil))
}

self.present(action, animated: true)

上面的代码将在iPhone上工作，但在iPad上运行时会崩溃，因为UIPopoverPresentationController将负责警报，它不会在那个时候引用任何东西。因此，为了避免这种情况，您必须提供以下代码块，这是强制性的

if let pop = action.popoverPresentationController {

     let v = sender as! UIView 
     pop.sourceView = v 
     pop.sourceRect = v.bounds
 }

同样，如果iPad点击弹窗之外的任何地方，它将被解散，.cancel操作按钮的完成处理程序将被调用。

也就是说，如果你有任何疑问，请在下方评论

不要在构造函数中提供otherbuttontitle。

let alertView = UIAlertView(title: "Oops!", message: "Something
happened...", delegate: nil, cancelButtonTitle: "OK")

alertView.show()

但我同意Oscar的观点，这个类在iOS 8中被弃用了，所以如果你只做iOS 8的应用程序，UIAlertView不会没有任何用途。否则上面的代码将工作。

使用此代码显示alertview

  let alertController = UIAlertController(title: "Hello  Coders", message: "your alert message", preferredStyle: .Alert)
        let defaultAction = UIAlertAction(title: "Close Alert", style: .Default, handler: nil)
        alertController.addAction(defaultAction)

        presentViewController(alertController, animated: true, completion: nil)

Swift显示警报使用UIAlertController

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)
  }
}

在Swift 4.2和Xcode 10中

方法一:

简单的提醒

let alert = UIAlertController(title: "Your title", message: "Your message", preferredStyle: .alert)
    
     let ok = UIAlertAction(title: "OK", style: .default, handler: { action in
     })
     alert.addAction(ok)
     let cancel = UIAlertAction(title: "Cancel", style: .default, handler: { action in
     })
     alert.addAction(cancel)
     DispatchQueue.main.async(execute: {
        self.present(alert, animated: true)
})

方法二:

使用共享类的警报

如果你想要共享类风格(写一次，随处使用)

import UIKit
class SharedClass: NSObject {//This is shared class
static let sharedInstance = SharedClass()

    //Show alert
    func alert(view: UIViewController, title: String, message: String) {
        let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let defaultAction = UIAlertAction(title: "OK", style: .default, handler: { action in
        })
        alert.addAction(defaultAction)
        DispatchQueue.main.async(execute: {
            view.present(alert, animated: true)
        })
    }

    private override init() {
    }
}

现在每个软件都调用这样的警报

SharedClass.sharedInstance.alert(view: self, title: "Your title here", message: "Your message here")

方法三:

显示所有窗口的警告顶部

如果您想在所有视图的顶部显示警报，请使用以下代码

func alertWindow(title: String, message: String) {
    DispatchQueue.main.async(execute: {
        let alertWindow = UIWindow(frame: UIScreen.main.bounds)
        alertWindow.rootViewController = UIViewController()
        alertWindow.windowLevel = UIWindowLevelAlert + 1
    
        let alert2 = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let defaultAction2 = UIAlertAction(title: "OK", style: .default, handler: { action in
        })
        alert2.addAction(defaultAction2)
    
        alertWindow.makeKeyAndVisible()
    
        alertWindow.rootViewController?.present(alert2, animated: true, completion: nil)
    })
}

函数调用

SharedClass.sharedInstance.alertWindow(title:"This your title", message:"This is your message")

方法四:

带扩展的警报

extension  UIViewController {

    func showAlert(withTitle title: String, withMessage message:String) {
        let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let ok = UIAlertAction(title: "OK", style: .default, handler: { action in
        })
        let cancel = UIAlertAction(title: "Cancel", style: .default, handler: { action in
        })
        alert.addAction(ok)
        alert.addAction(cancel)
        DispatchQueue.main.async(execute: {
            self.present(alert, animated: true)
        })
    }
}

现在像这样调用

//Call showAlert function in your class
@IBAction func onClickAlert(_ sender: UIButton) {
    showAlert(withTitle:"Your Title Here", withMessage: "YourCustomMessageHere")
}

方法五:

带有文本字段的警报

如果你想添加文本框提醒。

//Global variables
var name:String?
var login:String?

//Call this function like this:  alertWithTF() 
//Add textfields to alert 
func alertWithTF() {
    
    let alert = UIAlertController(title: "Login", message: "Enter username&password", preferredStyle: .alert)
    // Login button
    let loginAction = UIAlertAction(title: "Login", style: .default, handler: { (action) -> Void in
        // Get TextFields text
        let usernameTxt = alert.textFields![0]
        let passwordTxt = alert.textFields![1]
        //Asign textfileds text to our global varibles
        self.name = usernameTxt.text
        self.login = passwordTxt.text
        
        print("USERNAME: \(self.name!)\nPASSWORD: \(self.login!)")
    })
    
    // Cancel button
    let cancel = UIAlertAction(title: "Cancel", style: .destructive, handler: { (action) -> Void in })
    
    //1 textField for username
    alert.addTextField { (textField: UITextField) in
        textField.placeholder = "Enter username"
        //If required mention keyboard type, delegates, text sixe and font etc...
        //EX:
        textField.keyboardType = .default
    }
    
    //2nd textField for password
    alert.addTextField { (textField: UITextField) in
        textField.placeholder = "Enter password"
        textField.isSecureTextEntry = true
    }
    
    // Add actions
    alert.addAction(loginAction)
    alert.addAction(cancel)
    self.present(alert, animated: true, completion: nil)
    
}

方法6:

带扩展的共享类中的警报

//This is your shared class
import UIKit

 class SharedClass: NSObject {

 static let sharedInstance = SharedClass()

 //Here write your code....

 private override init() {
 }
}

//Alert function in shared class
extension UIViewController {
    func showAlert(title: String, msg: String) {
        DispatchQueue.main.async {
            let alert = UIAlertController(title: title, message: msg, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        }
    }
}

现在像这样直接调用

self.showAlert(title: "Your title here...", msg: "Your message here...")

方法7:

警报与共享类与扩展在单独的类警报。

创建一个新的Swift类，并导入UIKit。复制并粘贴下面的代码。

//This is your Swift new class file
import UIKit
import Foundation

extension UIAlertController {
    class func alert(title:String, msg:String, target: UIViewController) {
        let alert = UIAlertController(title: title, message: msg, preferredStyle: UIAlertControllerStyle.alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.default) {
        (result: UIAlertAction) -> Void in
        })
        target.present(alert, animated: true, completion: nil)
    }
}

现在在你所有的类中调用alert函数(单行)。

UIAlertController.alert(title:"Title", msg:"Message", target: self)

怎么样....