Stream3

class _StreamNumberState extends State<StreamNumber> {
  int lastNumber = 0;
  StreamTransformer? transformer;
  NumberStream? numberStream;
  StreamController? numberStreamController;
  @override
  void initState() {
    numberStream = NumberStream();
    numberStreamController = numberStream?.controller;
    Stream? stream = numberStreamController?.stream;
    // stream?.listen((event) {
    //   setState(() {
    //     lastNumber = event;
    //   });
    // });
    transformer = StreamTransformer<dynamic, dynamic>.fromHandlers(
        handleData: (value, sink) {
          sink.add(value * 10);
        },
        handleError: (error, trace, sink) {
          sink.add(-1);
        },
        handleDone: (sink) => sink.close());
    stream?.transform(transformer!).listen((event) {
      setState(() {
        lastNumber = event;
      });
    }).onError((error) {
      setState(() {
        lastNumber = -1;
      });
    });

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        width: double.infinity,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            Text(lastNumber.toString()),
            ElevatedButton(
              onPressed: () => addRandomNumber(),
              child: Text('New Random Number'),
            )
          ],
        ),
      ),
    );
  }

  void addRandomNumber() {
    Random random = Random();
    int myNum = random.nextInt(10);
    numberStream?.addNumberToSink(myNum);
  }
}