Swift 5和Xcode 10.2:

NotificationCenter.default.addObserver(
            self,
            selector: #selector(batteryLevelDidChangeNotification),
            name: UIDevice.batteryLevelDidChangeNotification,
            object: nil)

NSNotificationCenter在iOS 11的Swift 4.0中添加了观察者语法

  NotificationCenter.default.addObserver(self, selector: #selector(keyboardShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)

这是为keyboardWillShow通知名称类型。其他类型可以从可用选项中选择

选择器的类型是@objc func，它处理键盘的显示方式(这是你的用户函数)

在Swift 5中

我们说如果想从ViewControllerB接收数据到 ViewControllerA

ViewControllerA (Receiver)

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()

        //MARK: - - - - - Code for Passing Data through Notification Observer - - - - -
        // add observer in controller(s) where you want to receive data
        NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
    }

    //MARK: - - - - - Method for receiving Data through Post Notificaiton - - - - -
    @objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification : ", notification.object ?? "")
    }
}

视图控制器 B （发射器）

import UIKit

class ViewControllerB: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        //MARK: - - - - - Set data for Passing Data Post Notification - - - - -
        let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
    }

}

它与Objective-C API相同，但使用了Swift的语法。

Swift 4.2和Swift 5:

NotificationCenter.default.addObserver(
    self,
    selector: #selector(self.batteryLevelChanged),
    name: UIDevice.batteryLevelDidChangeNotification,
    object: nil)

如果你的观察者没有从Objective-C对象继承，你必须用@objc作为你的方法的前缀来使用它作为选择器。

@objc private func batteryLevelChanged(notification: NSNotification){     
    //do stuff using the userInfo property of the notification object
}

参见NSNotificationCenter类参考，与Objective-C api交互

我能够做以下之一成功地使用选择器-没有注释任何@objc:

NSNotificationCenter.defaultCenter().addObserver(self,
    selector:"batteryLevelChanged:" as Selector,
    name:"UIDeviceBatteryLevelDidChangeNotification",
    object:nil)    

OR

let notificationSelector: Selector = "batteryLevelChanged:"

NSNotificationCenter.defaultCenter().addObserver(self,
    selector: notificationSelector,
    name:"UIDeviceBatteryLevelDidChangeNotification",
    object:nil)    

我的xcrun版本显示Swift 1.2，这适用于Xcode 6.4和Xcode 7 beta 2(我认为会使用Swift 2.0):

$xcrun swift --version

Apple Swift version 1.2 (swiftlang-602.0.53.1 clang-602.0.53)

Xcode 8中的Swift 3.0

Swift 3.0已经用结构“包装器类型”取代了许多“字符串类型”的api, NotificationCenter也是如此。通知现在由struct notification标识。名称而不是字符串。参见迁移到Swift 3指南。

以前的用法:

// Define identifier
let notificationIdentifier: String = "NotificationIdentifier"

// Register to receive notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name: notificationIdentifier, object: nil)

// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationIdentifier, object: nil)

Swift 3.0的新用法:

// Define identifier
let notificationName = Notification.Name("NotificationIdentifier")

// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification), name: notificationName, object: nil)

// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)

所有系统通知类型现在都定义为notification . name上的静态常量;例如。uidevicebatteryleveldidchange， . uiapplicationdidfinishlaunching， . uitextfieldtextdidchange等。

您可以扩展通知。使用您自己的自定义通知命名，以便与系统通知保持一致:

// Definition:
extension Notification.Name {
    static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}

// Usage:
NotificationCenter.default.post(name: .yourCustomNotificationName, object: nil)