setState() vs notifyListeners(), which one is more efficient?

Question

I always aim to make my widgets Stateless instead Stateful for performance benefits. In some cases(updating the BottomNavigationBar index e.g.) notifyListeners() can provide identical functionality of the setState().

At first, I think notifyListener() is lower level, more fundemantal function comparing to setState(), so it should be more efficient. Because setState() method may triggers too many higher level framework methods, so it may spends more CPU power.

But it's hard to be sure without making a proper and detailed performance testing. So what is the answer?

Edit: Also, in some cases, notifyListeners() behaves exactly like setState(). For example, I have Text widget inside a StatelessWidget that holds a Random value and when I notify the an unrelated value inside the Class, the Text widget is also getting update. So, what is the difference?

Answer 1

Assuming that you're comparing ChangeNotifier.notifyListener with State.setState to rebuild the widget tree, then:

setState will always win.

The reason, notifyListener rebuilds your widget tree because it causes setState itself.

For notifyListener to work, there's usually a StatefulWidget somewhere in your tree that does the following:

class MyState extends State<T> {
  ChangeNotifier notifier;

  initState() {
    notifier.addListener(() => setState(() {}));
  }
}

In any case, this probably doesn't matter.