Counter app with stream

main.dart

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

// A counter app using Stream to manage state.

// counter.dart

int _count = 0;
final _controller = StreamController<int>()..add(_count);
Stream<int> counter() => _controller.stream;

void increment() => _controller.add(_count++);
void decrement() => _controller.add(_count--);

// main.dart

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Counter example')),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              StreamBuilder<int>(
                stream: counter(),
                builder: (context, snapshot) => Text('${snapshot.data}'),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  TextButton(
                      onPressed: () => increment(), child: const Text('+1')),
                  TextButton(
                      onPressed: () => decrement(), child: const Text('-1')),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}