StreamController StreamBuilder

 import "dart:async";

import "package:flutter/material.dart";

void main()
{
  runApp(const MyApp());
}
class MyApp extends StatelessWidget
{
  const MyApp({super.key});

  @override
  Widget build(BuildContext context)
  {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: HomePage(),
    );
  }
}
class HomePage extends StatefulWidget
{
  const HomePage({super.key});

  @override
  HomePageState createState()
  {
    return HomePageState();
  }
}

class HomePageState extends State<HomePage>
{
  int counter = 0;
  StreamController<int> counterController = StreamController<int>();

  @override
  Widget build(BuildContext context)
  {
    return Scaffold(
      body: SafeArea(
        child: Center(
          child: StreamBuilder(
            stream: counterController.stream,
            builder: (context, snapshot) {
              if(snapshot.hasData) {
                return Text(snapshot.data.toString(), style: const TextStyle(
                  fontSize: 70,
                  fontWeight: FontWeight.bold,
                ),);
              }
              else {
                return const Text("0", style: TextStyle(
                  fontSize: 70,
                  fontWeight: FontWeight.bold,
                ),);
              }
            }
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: (){
          counter++;
          counterController.sink.add(counter);
        },
        child: const Icon(Icons.add),
      ),
    );
  }
}