Scopes

[JCKodel]

I was tinkering some example project to use this (future) package, but I think I hit a limitation in it:

My use case is this:

I use an offline database eventually synced with a remote PostgreSQL database through PowerSync. PowerSync requires one database per user, so the database could only be initialized after the login and be disposed on logout.

So, I put this on my main.dart:

void main() {
  runApp(
    ECSScope(
      features: {
        AuthFeature(authRepo: FakeAuthRepo()),
      },
      child: const MainApp(),
    ),
  );
}

The main app shows a page depending on the auth state:

final class MainApp extends ECSWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context, ECSContext ecs) {
    final authStateComponent = ecs.watch<AuthStateComponent>();

    return MaterialApp(
      home: switch (authStateComponent.value) {
        UnknownAuthState() => const Center(child: CircularProgressIndicator()),
        LoggedInAuthState() => const HomePage(),
        LoggedOutAuthState() => const LoginPage(),
        SigningInAuthState() => const LoginPage(),
        ValidationErrorAuthState() => const LoginPage(),
      },
    );
  }
}

Perfect for this test. It works flawlessly (I admit it took some time for my two neurons to understand why I could not pass the credentials in the LogInEvent - until I realize the credentials are actually hold by a component).

Now, I wanted to simulate that case where I need to start up a database based on the authenticated user id, so, I did the next logical step, added a new scope wrapping my HomePage (my line of thought was: that scope will initialize stuff with InitializeSystem and it will be disposed when the scope is unloaded (i.e.: when the SignOutEvent is triggered):

final class MainApp extends ECSWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context, ECSContext ecs) {
    final authStateComponent = ecs.watch<AuthStateComponent>();

    return MaterialApp(
      home: switch (authStateComponent.value) {
        UnknownAuthState() => const Center(child: CircularProgressIndicator()),
        LoggedInAuthState() => ECSScope(
          features: {CounterFeature()},
          child: const HomePage(),
        ),
        LoggedOutAuthState() => const LoginPage(),
        SigningInAuthState() => const LoginPage(),
        ValidationErrorAuthState() => const LoginPage(),
      },
    );
  }
}

(notice: in this example, there is only a new CounterFeature, but here a DatabaseFeature would be created with initialization and disposal).

But this is not what happened: this code made SignOutEvent unavailable (I think the new ECSScope is overriding the main.app one).

So, two questions:

1. Should not ECSScope merge the features from the previous scope to the new one (same as get_it does?)

2. When that seconds ECSScope is unmounted by Flutter (example: when I sign out), all systems would be disposed (teardown)?

3. The initialization seems to be sync (void initialize()). I'm having trouble imagining how this particular database requirement fits in all of this (considering the features using in HomePage needs an initialized and opened database).

[FlameOfUdun]

Thanks for the detailed writeup! You’ve done a great job explaining your use case and walking through the code. It helps a lot.
The issue you are referring to is valid and is fixed in develop branch but not merged with main yet.
You can check it out.
Let me know if you face any further issues.
Cheers!

[FlameOfUdun]

Update: Just merge develop into main. Nested scopes are available now. Also added a devtools extension for easier use of ECS inspector. Check it out and tell me what you think. Cheers!