Sample Flutter bloc

counter_bloc.dart

import 'dart:async';
// import 'package:rxdart/rxdart.dart'; if you want to make use of PublishSubject, ReplaySubject or BehaviourSubject.
// make sure you have rxdart: as a dependency in your pubspec.yaml file to use the above import


class CounterBloc {
  final counterController = StreamController();  // create a StreamController or
  // final counterController = PublishSubject() or any other rxdart option;
  Stream get getCount => counterController.stream; // create a getter for our Stream
  // the rxdart stream controllers returns an Observable instead of a Stream
  
  void updateCount() {
    counterController.sink.add(data); // add whatever data we want into the Sink
  }
  
  void dispose() {
    counterController.close(); // close our StreamController to avoid memory leak
  }
}

final bloc = CounterBloc(); // create an instance of the counter bloc

//======= end of CounterBloc file



//======= somewhere else in our app
import 'counter_bloc.dart'; // import the counter bloc file here

@override
void dispose() {
  bloc.dispose(); // call the dispose method to close our StreamController
  super.dispose();
}

...
@override
Widget build(BuildContext context) {
  return StreamBuilder( // Wrap our widget with a StreamBuilder
    stream: bloc.getCount, // pass our Stream getter here
    initialData: 0, // provide an initial data
    builder: (context, snapshot) => Text('${snapshot.data}'), // access the data in our Stream here
  );
}
...