Swift 5通知观察员

override func viewDidLoad() {
    super.viewDidLoad() 
    NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelChanged), name: UIDevice.batteryLevelDidChangeNotification, object: nil)
}

@objc func batteryLevelChanged(notification : NSNotification){
    //do here code
}

override func viewWillDisappear(_ animated: Bool) {
    NotificationCenter.default.removeObserver(self, name: UIDevice.batteryLevelDidChangeNotification, object: nil)

}

我们也应该删除通知。

Ex.

deinit 
{
  NotificationCenter.default.removeObserver(self, name:NSNotification.Name(rawValue: "notify"), object: nil)

}

在swift 2.2 - XCode 7.3中，我们为NSNotificationCenter使用#选择器

 NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(rotate), name: UIDeviceOrientationDidChangeNotification, object: nil)

在swift 3, Xcode 8.2:-检查电池状态水平

//Add observer
NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: NSNotification.Name.UIDeviceBatteryStateDidChange, object: nil)


 //Fired when battery level changes

 func batteryStateDidChange(notification: NSNotification){
        //perform manipulation here
    }

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)