如何在 Swift 中将观察者添加到默认通知中心？我正在尝试移植这行代码，该代码行在电池电量变化时发送通知。

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryLevelChanged:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];

斯威夫特 4.0 和 Xcode 9.0+：

发送（邮寄）通知：

NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil)

OR

NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil, userInfo: ["Renish":"Dadhaniya"])

接收（获取）通知：

NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)

收到通知的函数方法处理程序：

@objc func methodOfReceivedNotification(notification: Notification) {}

斯威夫特 3.0 和 Xcode 8.0+：

发送（邮寄）通知：

NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil)

接收（获取）通知：

NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)

接收通知的方法处理程序：

func methodOfReceivedNotification(notification: Notification) {
  // Take Action on Notification
}

删除通知：

deinit {
  NotificationCenter.default.removeObserver(self, name: Notification.Name("NotificationIdentifier"), object: nil)
}

斯威夫特 2.3 和 Xcode 7：

发送（邮寄）通知

NSNotificationCenter.defaultCenter().postNotificationName("NotificationIdentifier", object: nil)

接收（获取）通知

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name:"NotificationIdentifier", object: nil)

接收通知的方法处理程序

func methodOfReceivedNotification(notification: NSNotification){
  // Take Action on Notification
}

对于历史 Xcode 版本...

发送（邮寄）通知

NSNotificationCenter.defaultCenter().postNotificationName("NotificationIdentifier", object: nil)

接收（获取）通知

NSNotificationCenter.defaultCenter().addObserver(self, selector: "methodOfReceivedNotification:", name:"NotificationIdentifier", object: nil)

删除通知

NSNotificationCenter.defaultCenter().removeObserver(self, name: "NotificationIdentifier", object: nil)
NSNotificationCenter.defaultCenter().removeObserver(self) // Remove from all notifications being observed

接收通知的方法处理程序

func methodOfReceivedNotification(notification: NSNotification) {
  // Take Action on Notification
}

使用@objc注释类或目标方法

@objc private func methodOfReceivedNotification(notification: NSNotification) {
  // Take Action on Notification
}

// Or

dynamic private func methodOfReceivedNotification(notification: NSNotification) {
  // Take Action on Notification
}