Flutter Stream example

main.dart

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

//wrapper class for progress + data
class DataWithProgress<T> {
  final T? data;
  final int progress; // 0..100
  final Object? error;
  final bool done;

  DataWithProgress({this.data, required this.progress, this.error, this.done = false});
}

// Producer (async* Beispiel)
Stream<DataWithProgress<int>> produce() async* {
  int total = 5;
  for (int i = 1; i <= total; i++) {
    await Future.delayed(Duration(seconds: 1));
    int progress = ((i / total) * 100).round();
    yield DataWithProgress(data: i, progress: progress);
  }
  // optional: endgültiger Done-Event
  yield DataWithProgress(progress: 100, done: true);
}

void main() async {
  final controller = StreamController<DataWithProgress>();
  
  // Listener
  print("1. Listener ---");
  controller.stream.listen((value) {
    print('Received progress: ${value.progress}%, data: ${value.data}');
  }, onDone: () => print('Stream closed (onDone)'),);
  
  
  // Adding data
  controller.sink.add(DataWithProgress(progress: 1));
  await Future.delayed(Duration(seconds: 1));
  controller.sink.add(DataWithProgress(progress: 33, data: 1));
  await Future.delayed(Duration(seconds: 2));
  controller.sink.add(DataWithProgress(progress: 66, data: 2));
  await Future.delayed(Duration(seconds: 1));
  controller.sink.add(DataWithProgress(progress: 99, data: 3));
  controller.sink.add(DataWithProgress(progress: 100, done: true));
  // Closing the stream
  controller.close();
  
  //consume stream with async* function
  print("2. consume stream with async* function ---");
  await for (final event in produce()) {
    if (event.data != null) print('Data: ${event.data} — ${event.progress}%');
    if (event.done) print('Producer signaled done');
  }
  print('Stream finished');
  
  //UI
  print("3. UI ---");
  runApp(const MyApp());

}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(home: ProgressDemoPage());
  }
}

class ProgressDemoPage extends StatefulWidget {
  const ProgressDemoPage({super.key});
  @override
  State<ProgressDemoPage> createState() => _ProgressDemoPageState();
}

class _ProgressDemoPageState extends State<ProgressDemoPage> {
  late Stream<DataWithProgress<int>> _stream;

  @override
  void initState() {
    super.initState();
    _stream = produce();
  }

  void _restart() {
    setState(() {
      _stream = produce();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Progress Stream Demo')),
      body: Center(
        child: StreamBuilder<DataWithProgress<int>>(
          stream: _stream,
          builder: (context, snapshot) {
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  CircularProgressIndicator(),
                  SizedBox(height: 12),
                  Text('Warte auf erste Updates...'),
                ],
              );
            } else if (snapshot.hasError) {
              return Text('Error: ${snapshot.error}');
            } else if (snapshot.hasData) {
              final e = snapshot.data!;
              final displayData = e.data != null ? 'Data: ${e.data}' : 'No data';
              return Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  Text(displayData, style: const TextStyle(fontSize: 24)),
                  const SizedBox(height: 12),
                  SizedBox(
                    width: 250,
                    child: LinearProgressIndicator(value: e.progress / 100),
                  ),
                  const SizedBox(height: 8),
                  Text('${e.progress}%'),
                  if (e.done) const Padding(
                    padding: EdgeInsets.only(top: 8.0),
                    child: Text('Fertig', style: TextStyle(color: Colors.green)),
                  ),
                ],
              );
            } else {
              return const Text('No data available');
            }
          },
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _restart,
        child: const Icon(Icons.replay),
      ),
    );
  }
}