iosswiftnsnotificationcenter

NSNotificationCenter addObserver in Swift

How do you add an observer in Swift to the default notification center? I'm trying to port this line of code that sends a notification when the battery level changes.

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

  • It's the same as the Objective-C API, but uses Swift's syntax.

    Swift 4.2 & Swift 5:

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

    If your observer does not inherit from an Objective-C object, you must prefix your method with @objc in order to use it as a selector.

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

    See NSNotificationCenter Class Reference, Interacting with Objective-C APIs