StreamExample

main.dart

import 'dart:async';
void main() {
 int count = 0;
 var counterController = new StreamController();
  counterController.stream.listen((value) => print(value));

  void increment() {
    counterController.add(count++);
  }

    final transformToString =
        new StreamTransformer.fromHandlers(handleData: (number, sink) {
      if (number.runtimeType == int) {
        sink.add("The counter is at $number!");
      } else {
        sink.addError("$number is not an int!");
      }
    });

    counterController.stream.map((input) => input).transform(transformToString);
  for(int i=0; i < 10; i++){
    increment();
  }
}