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

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