Documentation for connect()

[wstrange]

Not grokking how connect() works or why I would want to use it.

Some docs would be great!

[rodydavis]

Definitely want to add examples to the docs!

https://dartsignals.dev/async/connect/

The biggest reason to use it over StreamSignal is you work off of type T instead of AsyncState.

[wstrange]

In the example in the docs, how do you actually "advance" or consume the signal value when a new value is emitted from a stream? A more concrete example would really help. Something that consumes the connected signal.

[rodydavis]

You mean outside of using an effect?

[wstrange]

You mean outside of using an effect?

I'm honestly not sure I know the right question to ask.

If I have a Stream<Foo> I know I can create a stream signal from that. In my widget I'm going to get objects of AsyncState<Foo> - which is fine, I understand how to handle those (somewhat verbose, but it works).

Your previous comment implied I can 'connect' the stream to a non async signal, so my widget only deals with type Foo? And presumably only gets updated when the stream emits a new Foo into the "connected" signal?

A more complex example, ideally with a Flutter widget would really help.

[Jethro87]

+1, having a bit of trouble understanding connect.

[rodydavis]

It really depends on the data you are connecting to. I will present 2 examples for async data, user state and a database export event.

1. For user state the user is logged in or out but you don't want to handle when the stream or future is loading or has an error getting the signal. Only that there is a user or not. For this you would use connect.

final user$ = signal<User?>(null);
final Stream<User?> onAuthChanged = ...;
...
connect<User?>(user$) << onAuthChanged;

Also another common use case for connect is when working with RxDart.

2. You have a SQLite database and want to back it up on some interval. Here you would want to show when it is loading or have an error. In this case it would be a StreamSignal.

final Database db;
late final dbExport = Stream.periodic(Duration(minutes: 5), () => db.backup());
...
final export$ = dbExport.toSignal();

[Jethro87]

@rodydavis Thanks! The first example is my use case.

[Jethro87]

@rodydavis Sorry, one last question. In the following example, my appUser signal is always null. I suspect I'm doing something wrong in the effect and this line_appUserListener = connect(appUser) << appUserStream;, but I can't seem to figure it out. Any ideas? Appreciate it!

class AuthRepository {
  final auth = FirebaseAuth.instance;
  final _logger = locator<Logger>();

  AuthRepository() {
    _logger.i('$_serviceName: Initialized.');

    // Listen to the FirebaseAuth stream and update the current user
    _fbAuthListener = connect(currentUser) << auth.userChanges();

    // Set the uid of the current user
    currentUid = computed(() => currentUser.value?.uid, debugLabel: 'currentUid');

    // Listen to the uid of the current user and stream the app user.
    // Only update the appUser stream when the uid changes.
    effect(
      () {
        final uid = currentUid.value;

        _logger.i('$_serviceName: uid changed: $uid');

        if (uid != null && uid.isNotEmpty) {
          appUserStream = locator<FirestoreDatabase>().userStream(id: uid);
        } else {
          appUserStream = Stream.value(null);
        }
      },
    );

    // Listen to the stream and update the current app user
    _appUserListener = connect(appUser) << appUserStream;
  }

  // Current user signal
  final currentUser = signal<User?>(null, debugLabel: 'currentUser');

  // First value of auth state changes
  late final FutureSignal<User?> waitForInitialUser =
      computedAsync(() => auth.userChanges().first, debugLabel: 'waitForInitialUser');

  // Current user uid
  late final Computed<String?> currentUid;

  // Current app user signal
  final appUser = signal<AppUser?>(null, debugLabel: 'appUser');

  // Computed signal that only emits when the user is logged in / out
  late final Computed<bool> isLoggedIn = computed(() => currentUser() != null, debugLabel: 'isLoggedIn');

  // Listen to auth state changes and update the current user
  late Connect<User?, User?> _fbAuthListener;

  // Stream of the current user
  late Stream<AppUser?> appUserStream;

  // Listen to auth state changes and update the current app user
  late Connect<AppUser?, AppUser?> _appUserListener;

  // Dispose of the stream controller
  void dispose() {
    _fbAuthListener.dispose();
    _appUserListener.dispose();
    _logger.i('$_serviceName: Disposed.');
  }
}

[rodydavis]

You have to set up the connect and add the stream separately.

I was having issues trying to define them both in the late initializers but would work if I added the stream in an init method