How can I use applicationDidBecomeActive in UIViewController?

Swift 3:

NotificationCenter.default.addObserver(
    self,
    selector: #selector(applicationDidBecomeActive(_:)),
    name: NSNotification.Name.UIApplicationDidBecomeActive,
    object: nil)



func applicationDidBecomeActive(_ notification: NSNotification) {
    // do something
}

Note: Don't forget to remove the observer

Here is an example of registering a notification handler in Swift (adapted from Apurv's answer above):

override func viewDidLoad() {
    super.viewDidLoad()

    NotificationCenter.default.addObserver(
        self,
        selector: #selector(applicationDidBecomeActive(notification:)),
        name: NSNotification.Name.UIApplicationDidBecomeActive,
        object: nil)
}

@objc func applicationDidBecomeActive(notification: NSNotification) {
    // do something
}

Update for Swift 4.2:

override func viewDidLoad() {
    super.viewDidLoad()

    NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
}

@objc func applicationDidBecomeActive(notification: NSNotification) {
    // Application is back in the foreground

    print("active")
}

At the time of reactivation, if you want to carry a particular thing for a view controller, you should register a notification in its viewDidLoad method.

UIApplicationDidBecomeActiveNotification will automatically notify your application and given controller, if they registered for it.

 [[NSNotificationCenter defaultCenter]addObserver:self
                                         selector:@selector(yourMethod)
                                             name:UIApplicationDidBecomeActiveNotification
                                           object:nil];