main.dart

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

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

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page with Streams'),
      debugShowCheckedModeBanner: false,
    );
  }
}

//View One
class MyHomePage extends StatelessWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);
  String title;

  void _incrementCounter() {
    CounterService().incValue();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
        actions: [
          IconButton(
            icon: Icon(Icons.adaptive.arrow_forward),
            onPressed: () {
              Navigator.of(context).push(
                MaterialPageRoute(builder: (_) {
                  return SecondPage(title: "SecondPage");
                }),
              );
            },
          ),
        ],
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<CounterModel>(
                stream: CounterService().getStream(),
                builder: (context, snapshot) {
                  if (!snapshot.hasData && !snapshot.hasError) {
                    return CircularProgressIndicator();
                  }
                  if (snapshot.hasData) {
                    print("has data");
                    print(snapshot.data!.counter);
                    var data = snapshot.data!.counter;
                    if (data == null) {
                      return CircularProgressIndicator();
                    }
                    print(data);
                    return Text(
                      'Data in Stream is $data',
                      style: Theme.of(context).textTheme.headline4,
                    );
                  } else {
                    print("has error second screen");
                    var error = snapshot.error;
                    return Text('$error');
                  }
                })
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}


//second view
class SecondPage extends StatelessWidget {
  SecondPage({Key? key, required this.title}) : super(key: key);
  String title;

  void _incrementCounter() {
    CounterService().incValue();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<CounterModel>(
                stream: CounterService().getStream(),
                builder: (context, snapshot) {
                  if (!snapshot.hasData && !snapshot.hasError) {
                    return CircularProgressIndicator();
                  }
                  if (snapshot.hasData) {
                    print("has data");
                    print(snapshot.data!.counter);
                    var data = snapshot.data!.counter;
                    if (data == null) {
                      return CircularProgressIndicator();
                    }
                    print(data);
                    return Text(
                      'Data in Stream is $data',
                      style: Theme.of(context).textTheme.headline4,
                    );
                  } else {
                    print("has error second screen");
                    var error = snapshot.error;
                    return Text('$error');
                  }
                })
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}


//service

class CounterModel {
  CounterModel({int? this.counter}) {}
  int? counter;
}

class CounterService {
  static final CounterService _singleton = CounterService._internal();
  static final StreamController<CounterModel> streamController =
      StreamController<CounterModel>.broadcast();
  static final rng = Random();
  factory CounterService() {
    return _singleton;
  }

  late CounterModel counter = CounterModel(counter: 0);

  CounterService._internal() {}

  Stream<CounterModel> getStream() {
    Future.delayed(Duration(seconds: 0), () {
      streamController.add(counter);
    });

    return streamController.stream;
  }

  void incValue() async {
    var randomd = rng.nextBool();
    streamController.add(CounterModel());
    await Future.delayed(Duration(seconds: 2));
    if (randomd) {
      print("add data");
      counter.counter = counter.counter! + 1;
      streamController.add(counter);
    } else {
      streamController.addError("Test Error");
    }
  }
}