Dependency Injection without external packages

[anthonyaquino83]

Hi @rodydavis, I know signals is a reactivity library but I was thinking...

• Bloc has RepositoryProvider and MultiRepositoryProvider to be used as a DI.
• Riverpod has the simple Provider to be used as DI.
  I don't like to use get_it with bloc or riverpod, and Remy and Felix don't recommmend it because the mentioned above.

Would it be a good practice achieve DI in signals with untracked? Like an AuthenticationRepository class signal?
Can you make some utility for this? I thought it could be a readonlySignalContainer but the doc says it "will return new ones every time".
Let's go, brother Rody. 😎

[rydmike]

It has what @rodydavis calls an "experimental" inherited widget in V5 SignalProvider, that is built-in.

See https://dartsignals.dev/guides/dependency-injection/#inheritedwidget and https://pub.dev/documentation/signals/latest/signals_flutter_extended/SignalProvider-class.html and also a ComputedProvider https://pub.dev/documentation/signals/latest/signals_flutter_extended/ComputedProvider-class.html.

It is a start at least, I think Rody might have some plans on how to evolve this further in a later release.

I recommend checking out lite_ref and context_ref alternatives, but yeah those are external packages too, both quite neat though.

[anthonyaquino83]

Thanks, @rydmike, I will make some experiments creating repositories with SignalProvider. Very interesting.
Edit.: a MultiSignalProvider would be interesting... It's very common we have multiple repositories. :)

[rodydavis]

For never subscribing and never mutating you could create a signal like this:

final ReadonlySignal<Database> db = (){
  final Database connection = ...;
  final instance = signal(connection, autoDispose: true);
  instance.onDispose(() => connection.close());
  return instance;
}();

Or simpler approach that just makes a value readonly and a singleton:

final ReadonlySignal<SharedPreferences> prefs = signal(...);

void main() async {
  // Explicitly cast to set value
  (prefs as Signal<SharedPreferences>).value = await SharedPreferences.getInstance();
  ...
}

For both of these, .value will cause a 1 time subscription, but what you want is .peek() which will just return the value without subscribing.

For MultiProvider you can actually use nested which is what they both use.