Flutter - StreamBuilder with setState

main.dart

import 'package:flutter/material.dart';
import 'dart:async';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyHome(),
        ),
      ),
    );
  }
}

class MyHome extends StatefulWidget {
  const MyHome({super.key});

  @override
  State<MyHome> createState() => _MyHomeState();
}

class _MyHomeState extends State<MyHome> {
  StreamController<String> streamController = StreamController();
  int number = 0;

  final Stream<int> _bids = (() {
    late final StreamController<int> controller;
    controller = StreamController<int>.broadcast(
      onListen: () async {
        await Future<void>.delayed(const Duration(seconds: 1));
        controller.add(1);
        await Future<void>.delayed(const Duration(seconds: 1));
        controller.add(2);
        await Future<void>.delayed(const Duration(seconds: 1));
        controller.add(4);
        await Future<void>.delayed(const Duration(seconds: 1));
        await controller.close();
      },
    );
    return controller.stream;
  })();
  
 
  @override
  initState(){
    super.initState();
    
    _bids.listen((val) => setState((){
      number = val;
    }));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Iteration $number")),
      body: StreamBuilder<int>(
        stream: _bids,
        
        builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
          List<Widget> children;
          if (snapshot.hasError) {
            children = <Widget>[
              const Icon(
                Icons.error_outline,
                color: Colors.red,
                size: 60,
              ),
              Padding(
                padding: const EdgeInsets.only(top: 16),
                child: Text('Error: ${snapshot.error}'),
              ),
              Padding(
                padding: const EdgeInsets.only(top: 8),
                child: Text('Stack trace: ${snapshot.stackTrace}'),
              ),
            ];
          } else {
            print("calling");
//             setState((){
//               number = snapshot.data!.toInt();
//             });
            switch (snapshot.connectionState) {
              case ConnectionState.none:
                children = const <Widget>[
                  Icon(
                    Icons.info,
                    color: Colors.blue,
                    size: 60,
                  ),
                  Padding(
                    padding: EdgeInsets.only(top: 16),
                    child: Text('Select a lot'),
                  ),
                ];
                break;
              case ConnectionState.waiting:
                children = const <Widget>[
                  SizedBox(
                    width: 60,
                    height: 60,
                    child: CircularProgressIndicator(),
                  ),
                  Padding(
                    padding: EdgeInsets.only(top: 16),
                    child: Text('Awaiting bids...'),
                  ),
                ];
                break;
              case ConnectionState.active:
                children = <Widget>[
                  const Icon(
                    Icons.check_circle_outline,
                    color: Colors.green,
                    size: 60,
                  ),
                  Padding(
                    padding: const EdgeInsets.only(top: 16),
                    child: Text('\$${snapshot.data}'),
                  ),
                ];
                break;
              case ConnectionState.done:
                children = <Widget>[
                  const Icon(
                    Icons.info,
                    color: Colors.blue,
                    size: 60,
                  ),
                  Padding(
                    padding: const EdgeInsets.only(top: 16),
                    child: Text('\$${snapshot.data} (closed)'),
                  ),
                ];
                break;
            }
          }

          return Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: children,
            ),
          );
        },
      ),
    );
  }
}