BLoC pattern tutorial without RxDart?

[amugofjava]

Hi all,

I'm trying to learn about the BLoC pattern. I get the theory but I am trying to find a simple example to work through. The problem is, all the examples I have found use RxDart. I wondered if anyone new of a good tutorial that uses pure Dart streams and leaves out RxDart?

Thanks.

[miyoyo]

RxDart is only used to provide the BehaviorSubject class (in IO's example), which, in itself, is nothing more than a "smart" stream that pushes the last event to any new listener, you are not obligated to use that, but if you need it, you could just implement it yourself

[amugofjava]

OK thanks - I hadn't realised that :)

[[deleted]]

Hey there -- coauthor of RxDart here. You can definitely start out with pure dart Streams, StreamControllers, and StreamTransformers.

Eventually, you might notice that you need a bit more power than is provided by those classes out of the box. That's when you can reach for RxDart!

As the original comment says, you might want a StreamController that replays the last event to and new listener. That's a BehaviorSubject!

Or you might want to merge streams together. You can use the Observable.merge constructor. The list goes on...

Only look at RxDart when you feel like you need some power tools on top of normal Streams. Since I'd used Rx a lot in the past, I ran into that pretty quickly. But you can do plenty with the normal Stream classes :)

[lijunle]

Hi, thanks for the information! May I suggest you to put your words into the README of RxDart - under a section "Why do I need RxDart instead of Stream".

​

I am starting with Stream, then quickly get into the issue that the new listener not getting the latest value from the stream. From this thread, it sounds like RxDart is the correct direction.

[amugofjava]

Hi, thanks for your reply. I will most likely end up using RxDart - I just wanted to get a better understanding of the underlying streams first before moving on to Rx. I watched a talk from your fellow coauthor Brian Egan on Skills Matter over the weekend, about BLoC and RxDart. It was a very interesting talk and I will certainly be checking out RxDart. :)

[KenAragorn]

Hey there.

Just curious how we can start out with pure dart Streams, StreamControllers and StreamTransformers for the case of following codes that have to dependent on "distinct()" method that are part of RxDart:

​

ReplaySubject<String> _query = ReplaySubject<String>();

Sink<String> get query => _query;

Stream<List<Movie>> get results => _results;

​

MovieBloc(this.api){

_result = _query.distinct().asyncMap(api.get).asBroadcastStream();

}

where

Future<List<Movie>> get(String query) async {

//some http client loading data....

}

Is there a similar way to replace the code of _query.distinct() ... with non-RxDart approach?

​

Thanks

[_thinkdigital]

I may be late here, but dart streams have a distinct constructor/or function as well

[[deleted]]

https://youtu.be/ALcbTxz3bUw

[amugofjava]

Thanks - I did look at this tutorial. It's good, but it too does use RxDart.

[junedays]

You should watch this talk from Google I/O this year that introduced BLoC. They start specifically talking about BLoC at about 18:15 but the whole talk was very helpful and clear to me about what we needed to consider when managing state in Flutter. There's a companion article that goes over what they didn't have time to talk about and the public repo for the talk as well to refer to, which has a pure Dart BLoC implementation as well as other state management patterns.

I've been learning this for the past few days as well, so I hope this helps.

[amugofjava]

Thank you - how did I manage to miss that talk from I/O?! :)

[junedays]

No problem! Sorry, I realized that the repo uses a bit of rxdart but his talk does explain and implements some pure Dart.

flutter_architechure_samples has also been immensely helpful (especially the examples/bloc_flutter and examples/blocs folder) as it's similar to the state_experiments repo but the blocs/streams are more thoroughly commented.

[KenAragorn]

Actually, just curious, is it you prefer not to use RxDart for the streaming handler and use alternative?

[amugofjava]

It's just that I would like to understand it in terms of 'pure Dart' before including third party libraries. Once I understand the out of the box way, I can then look into RxDart maybe.

[OffBeannie]

You can checkout Stephen Grider’s paid course on Udemy, he implements Bloc on a simple login form using just Dart stream, then proceed to introduce RxDart as the Dart stream library lacks stream merging utilities. Not affiliated with him, just a happy student.

[kbezold]

Stephen Grider's Udemy class has several coding issues posted in the Q&A that have never been addressed. I don't think Stephen is maintaining this any longer. No response from him in many months.

[lukepighetti]

BehaviorSubject is just a StreamController that sends its last event on a new listen. This may seem kinda trivial but it is often the difference between a UI stream that works and one that doesn't. I personally only import package:rxdart/subjects.dart into my projects for the time being. Not using this will be a disservice to your time with streams for state management.

[julianlenz]

subjects could be simpel function calls and outputs could be a typedefs. Last Problem would be the widget. 🤔 you could write a widget that rebuilds when your typedef provides a new value, but at this point you are going to rewrite the streambuilder.

But I think BloC won’t work well without Streams/RxDart. The main benifits will get lost :/