How to tell the active view controller when applicationDidBecomeActive is called?

Question

I feel I am missing a trick here...

I just want to call viewDidLoad or viewDidAppear on the current active view controller when applicationDidBecomeActive gets called, s

Answer 1

Ok so it's pretty catastrophic.

You guys have to pay attention to events registration/unregistration cause you can cause memory leaks.

To make everything work you need to set a flag which knows what's the registration status: either you signed to background events or not. Notice that you need to register to the events when the view controller is seen by the user (if he came from a different one) or if he came from the home screen to your view controller.

You also need to unregister when you leave the view controller to a different one.

In short:

Swift 4:

private var registeredToBackgroundEvents = false

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    registerToBackFromBackground()
}

/// register to back from backround event
private func registerToBackFromBackground() {
    if(!registeredToBackgroundEvents) {
        NotificationCenter.default.addObserver(self, 
        selector: #selector(viewDidBecomeActive), 
        name: UIApplication.didBecomeActiveNotification, object: nil)
        registeredToBackgroundEvents = true
    }
}

/// unregister from back from backround event
private func unregisterFromBackFromBackground() {
    if(registeredToBackgroundEvents) {
        NotificationCenter.default.removeObserver(self, 
        name: UIApplication.didBecomeActiveNotification, object: nil)
        registeredToBackgroundEvents = false
    }

}

@objc func viewDidBecomeActive(){
    logicManager.onBackFromStandby()
}


override func viewWillDisappear(_ animated: Bool) {
    unregisterFromBackFromBackground()
}