in Flutter, what is the difference between .addListener(nofityListeners) and .notifyListeners?

Question

I am not even sure xxManager.notifyListeners() is valid because what I saw so far is just plain notifyListeners() being used in class that extend ChangeNotifier for example :

 Timer(
      const Duration(milliseconds: 2000),
      () {
        _initialized = true;
        notifyListeners();
      },
    );

here i tried to understand the meaning of

class AppRouter extends RouterDelegate<AppLink>
    with
        ChangeNotifier,
        PopNavigatorRouterDelegateMixin {
  @override
  final GlobalKey<NavigatorState> navigatorKey;

  final AppStateManager appStateManager;
  final XXManager xxManager;
  final YYManager yyManager;

  AppRouter({
    required this.appStateManager,
    required this.xxManager,
    required this.yyManager,
  })
      : navigatorKey = GlobalKey<NavigatorState>() {
    appStateManager.addListener(notifyListeners);       <-------This part
.
.
.
}

that part of the code for what I understand is to add listener to see the change in appStateManager which if changes will trigger notifyListeners method. what i dont understand is when i change it into:

appStateManager.notifyListeners();

it didnt show any error but when I ran it apparently it does not listen nor notify (the appStateManager has a Timer function which change the state in this case isInitialized to true after 2s so if the listener catch it, it will "route to next widget" (hope i said it correctly)). with 1st case it will change screen after 2s but on 2nd case it does nothin. what is wrong?

Answer 1

It's pretty straight forward.
appStateManager.addListener() adds listeners.
appStateManager.notifyListeners() notifies those listeners.

But with this line:
appStateManager.addListener(notifyListeners);
You are adding listeners with the name notifyListeners. notifyListeners is a variable here. It's not the same as the method

Answer 2

addListener is register a closure to be called when the object changes.

notifyListeners is Calling all the registered listeners.

Note that:

• with addListener, if you want to add an instance, then it must be removed the same number of times it is added before it will stop being called.
• these methods must not be called after dispose has been called.