ReactiveX/rxdart

Frank Pepermans

@frankpepermans

In the meantime, 2 wheres are not that bad

kimjisung78

@kimjisung78

Hello. I have made pagination using by rxdart. Which Subject choose?

Frank Pepermans

@frankpepermans

@kimjisung78 that's a pretty vague question, are you asking what the different Subjects do?

kimjisung78

@kimjisung78

I'm sorry to leave you with such a difficult question. I can’t understand the difference between PublishSubject and BehaviorSubject. And I don’t know “Which one is better if I want to make pagination?”

Frank Pepermans

@frankpepermans

@kimjisung78 they both allow multiple subscribers, but the difference is that when subscribing to a BehaviorSubject, then the last added event will be replayed immediately.

schmidtfx

@schmidtfx

Hello everyone, I'm fairly new to rxdart. I have heard about doOnDone. How would I trigger the done on an subject?

Frank Pepermans

@frankpepermans

@schmidtfx you need to call close()

Deva Palanisamy

@devapalanisamy

Hi, is there guide when to use operator and which operator to use for rxdart? Thanks

Like this one https://xgrommx.github.io/rx-book/content/which_operator_do_i_use/index.html

Frank Pepermans

@frankpepermans

RxDart has much in common with RxJs, or other Rx implementations, we don't have an equivalent in RxDart

Deva Palanisamy

@devapalanisamy

@frankpepermans thanks for creating powerful library

Matias Meno

@enyo

Hi! Just made the 22_to_23 switch

so far everything seemed to work fine, but there's one error that I get now:

.shareValue() doesn't exist anymore

Ah!

Since it's an extension I need to import rxdart for it to exist.

Got it :)

Great job! Thanks for also providing the codemod

One suggestion though: add the .seeded() factory constructor to the codemod

I had to replace all of this manually

Frank Pepermans

@frankpepermans

great :) we're on 0.24.1 meanwhile, but that shouldn't be too big a change

Rafael Corbellini

@rafaelcorbellini-egsys

Hello, I would like to know how do I execute a function when something is emitted (sink / add) in the controller, I know doOnData but it only works if someone is listening to the stream.

Jack Reilly

@jackdreilly

I have a common usage where I want a ValueStream which doesn't shut down when it no longer has listeners. You could imagine that you have a global ValueStream for a Firestore document, and you never want this stream to close due to changes in the number of subscribers, e.g. The workaround I have right now is to register a no-op listener upon creation of the ValueStream, which then "tricks" the stream into thinking it always has a listener. Is there a better pattern I could adopt for this?

Frank Pepermans

@frankpepermans

@rafaelcorbellini-egsys Streams by design only become active after an initial subscription, doOnX would then be a good choice like you mentioned.

Frank Pepermans

@frankpepermans

@jackdreilly since rxdart is built upon the Dart Streams, a ValueStream is like a broadcast Stream, see https://api.flutter.dev/flutter/dart-async/StreamController/StreamController.broadcast.html

So no, to prevent onCancel, a dummy listener could be a solution in your case

Jack Reilly

@jackdreilly

@frankpepermans thanks for the help and the broadcast documentation, very helpful in understanding the motivation behind the behavior

lively-bigyan

@lively-bigyan

Can I use rxsubject without disposing it?

Matias Meno

@enyo

When I have a ValueStream and I want to map the values, is there a convenient way to map to another ValueStream?
Right now I'm using this:

user.map((u) => u != null).shareValueSeeded(user.value != null)

lizzardman

@lizzardman

I just ended up writing custom extension for this

Matias Meno

@enyo

@lizzardman yeah just doing the same

I'm still being surprised by the behaviour of ValueStream :-/

Like, you do this:

newStream = old.map(mapping).shareValue(mapping);
old.add('foo');
newStream.value == 'foo'; // That's not the case

So, unless anyone is listening to the stream, it won't update .value properly

Matias Meno

@enyo

I know it's not really rxdarts fault, but it's still a common pitfall for me.

Frank Pepermans

@frankpepermans

We ideally want to fix this, map is native and returns a MapStream, which isn't a ValueStream. In beta 2 all rx ops do keep the type of the original stream

Matias Meno

@enyo

@frankpepermans oooh, that sounds great. Does that mean, that a map will work even without a listener?

Or is this problem going to persist

Frank Pepermans

@frankpepermans

Without a listener? No, basically everything triggers upon onListen internally

Matias Meno

@enyo

Hi. I've just started implementing the bloc library in my app, and used their example for a form. I've realised this issue: felangel/bloc#1888

Could somebody help me find a solution to do this properly?

So basically, there are events that represent an input field change (EmailChanged and PasswordChanged events)

To avoid rebuilding the form and doing unnecessary validations, these are debounced:

final debounced = events
        .where((event) => event is! FormSubmitted)
        .debounceTime(const Duration(milliseconds: 300));

They are then merged with the FormSubmitted event like this:

return events
        .where((event) => event is FormSubmitted)
        .mergeWith([debounced])

The problem with that is, that EmailChangedand PasswordChanged events could be triggered, being debounced, and then the FormSubmitted event could arrive, and be handled before the change events are being handled

Matias Meno

@enyo

Is there an elegant way to handle this issue with rxdart?

Frank Pepermans

@frankpepermans

For sure,

You could go with combineLatest or switchMap for starters, can the submit only happen when both fields are valid?

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