Feature Request: `useListener` hook

[gruvw]

Is your feature request related to a problem? Please describe.

When using Listenable with useEffect it can be a bit cumbersome to always repeat the same boilerplate off addListener and removeListener again and again:

• Having to call keys.length times addListener
• Duplication of key in keys and key.addListener(...) for each key
• Extra level of indentation when writing the listener inside the useEffect closure

Describe the solution you'd like

Add a useListener hook.

void useListener(void Function() listener, List<Listenable> listenables) {
  useEffect(() {
    final listenable = Listenable.merge(listenables);
    listenable.addListener(listener);

    return () => listenable.removeListener(listener);
  }, listenables);
}

Additional context

This would be very useful to bind values when some controller changes:

final nameError = useState<String?>(null);
final nameController = useTextEditingController();

useListener(() {
  final validation = nameValidation(offlineNameController.text);
  nameError.value = validation.nameError;
}, [nameController]);

and even when it depends on multiple controllers like:

final activeTab = useState(_initialTab);
final primaryTabController = useTabController(
  initialLength: Tabs.primaryTabLength,
  initialIndex: activeTab.value.primaryTabIndex,
);
final secondaryTabController = useTabController(
  initialLength: Tabs.secondaryTabLength,
  initialIndex: activeTab.value.secondaryTabIndex,
);

useListener(() {
  activeTab.value = Tabs.of(
    primaryTabController.index,
    secondaryTabController.index,
  );
}, [
  primaryTabController,
  secondaryTabController,
]);

[rrousselGit]

The naming would more more "useOnListenableChange", like "useOnStreamChange" And it would take a single listenable, not a list of listenable.

Otherwise LGTM. Feel free to make a PR if you want to :)

[gruvw]

Ok sure I will try and make a PR! Let me know if I mess up something doing so as it's only my second one :)

However why not a list of listenables ? It's more convenient isn't it ?

[rrousselGit]

Folks wanting to listen to multiple listenables can use the hook multiple times or use Listenable.merge

It's rare that they'll want to listen to multiple listenables at once.