Understanding RXDart Streams

Types of subjects in RxDart

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Standard Subject	Publisher Subject
The base for all Subjects. If you'd like to create a new Subject, extend from this class.	Exactly like a normal broadcast StreamController with one exception: this class is both a Stream and Sink.

Behaviour Subject	Replay Subject
A special StreamController that captures the latest item that has been added to the controller, and emits that as the first item to any new listener.	A special StreamController that captures all of the items that have been added to the controller, and emits those as the first items to any new listener.

Implementation

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1. Build a BLoC class and create four subject streams

final _dartStream = StreamController<String>();
final _publishStream = PublishSubject<String>();
final _behaviourStream = BehaviorSubject<String>();
final _replayStream = ReplaySubject<String>();

2. Write the main function that calls from the widget, for this application its startReading()

startReading() async {
    Future<String> loadAsset() async {
      return await rootBundle.loadString('assets/sonnet.txt');
    }
    var contents = loadAsset();
    contents.then((value) {
      print(value);
    });
  }

3. Wrap the main method with Provider class

return Provider(
      create: (context) => ReaderBloc(),
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.red,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: Launch(),
      ),
    );

4. Then create a ReaderBloc instance in the widget

readerBloc = Provider.of<ReaderBloc>(context);

5. Call the method using the bloc instance

readerBloc.startReading();

Notes

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All of the RxDart streams are multiple subscription, but StreamController is single subscription. So you get to listen once to the stream. So if you want to listing with multiple subscriptions you need to add asBroadcastStream to the StreamController.

Stream<String> get dartStream => _dartStream.stream.asBroadcastStream();

How it all Works?

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BehaviorSubject remembers the previous value and get that value.

PubishSubject does't get the current value, instead it gets the value to come down next. This is exactly like a broadcast StreamController

ReplaySubject tracks all history of value that is added to the stream. We can cap the values that kept in the stream.