Lernen Streams for Real-Time Flutter UIs | Asynchronous Dart in Flutter

Dart Streams are a powerful way to handle asynchronous sequences of data. In Flutter, you use Streams to listen for real-time updates—such as user actions, network responses, or sensor data—and update your UI instantly as new events arrive. Unlike Future, which returns a single value, a Stream delivers many values over time, making it ideal for chat messages, search suggestions, or live feeds.

main.dart


              123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
            
import 'dart:async';
import 'package:flutter/material.dart';

void main() => runApp(StreamDemoApp());

class StreamDemoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: StreamCounterWidget(),
    );
  }
}

class StreamCounterWidget extends StatefulWidget {
  @override
  _StreamCounterWidgetState createState() => _StreamCounterWidgetState();
}

class _StreamCounterWidgetState extends State<StreamCounterWidget> {
  final StreamController<int> _controller = StreamController<int>();
  int _counter = 0;

  @override
  void initState() {
    super.initState();
    // Emit a new value every second
    Timer.periodic(Duration(seconds: 1), (timer) {
      _controller.sink.add(++_counter);
      if (_counter >= 5) timer.cancel();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Stream Counter')),
      body: Center(
        child: StreamBuilder<int>(
          stream: _controller.stream,
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              return Text('Counter: [${snapshot.data}',
                  style: TextStyle(fontSize: 24));
            } else {
              return Text('Waiting for data...',
                  style: TextStyle(fontSize: 24));
            }
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    _controller.close();
    super.dispose();
  }
}

When you work with Streams in Flutter, you will often use a StreamController to add data to a stream and manage its lifecycle. Subscribing to a stream gives you a StreamSubscription, which you must manage carefully—especially in stateful widgets—to avoid resource leaks or unexpected behavior.

main.dart


              1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253
            
import 'dart:async';
import 'package:flutter/material.dart';

void main() => runApp(SubscriptionDemoApp());

class SubscriptionDemoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: SubscriptionWidget(),
    );
  }
}

class SubscriptionWidget extends StatefulWidget {
  @override
  _SubscriptionWidgetState createState() => _SubscriptionWidgetState();
}

class _SubscriptionWidgetState extends State<SubscriptionWidget> {
  final StreamController<String> _controller = StreamController<String>();
  StreamSubscription<String>? _subscription;
  String _latest = "No data";

  @override
  void initState() {
    super.initState();
    _subscription = _controller.stream.listen((data) {
      setState(() {
        _latest = data;
      });
    });
    // Simulate incoming data
    Future.delayed(Duration(seconds: 1), () {
      _controller.add("Hello from Stream!");
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('StreamSubscription Example')),
      body: Center(child: Text(_latest, style: TextStyle(fontSize: 24))),
    );
  }

  @override
  void dispose() {
    _subscription?.cancel();
    _controller.close();
    super.dispose();
  }
}

Note

Always cancel your StreamSubscriptions in the dispose method of a stateful widget. Failing to do so can cause memory leaks and unexpected behavior, as the widget may continue to listen to data even after it is removed from the widget tree.

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 2

Fragen Sie AI

Fragen Sie alles oder probieren Sie eine der vorgeschlagenen Fragen, um unser Gespräch zu beginnen

Swipe um das Menü anzuzeigen

main.dart


              123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
            
import 'dart:async';
import 'package:flutter/material.dart';

void main() => runApp(StreamDemoApp());

class StreamDemoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: StreamCounterWidget(),
    );
  }
}

class StreamCounterWidget extends StatefulWidget {
  @override
  _StreamCounterWidgetState createState() => _StreamCounterWidgetState();
}

class _StreamCounterWidgetState extends State<StreamCounterWidget> {
  final StreamController<int> _controller = StreamController<int>();
  int _counter = 0;

  @override
  void initState() {
    super.initState();
    // Emit a new value every second
    Timer.periodic(Duration(seconds: 1), (timer) {
      _controller.sink.add(++_counter);
      if (_counter >= 5) timer.cancel();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Stream Counter')),
      body: Center(
        child: StreamBuilder<int>(
          stream: _controller.stream,
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              return Text('Counter: [${snapshot.data}',
                  style: TextStyle(fontSize: 24));
            } else {
              return Text('Waiting for data...',
                  style: TextStyle(fontSize: 24));
            }
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    _controller.close();
    super.dispose();
  }
}

main.dart


              1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253
            
import 'dart:async';
import 'package:flutter/material.dart';

void main() => runApp(SubscriptionDemoApp());

class SubscriptionDemoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: SubscriptionWidget(),
    );
  }
}

class SubscriptionWidget extends StatefulWidget {
  @override
  _SubscriptionWidgetState createState() => _SubscriptionWidgetState();
}

class _SubscriptionWidgetState extends State<SubscriptionWidget> {
  final StreamController<String> _controller = StreamController<String>();
  StreamSubscription<String>? _subscription;
  String _latest = "No data";

  @override
  void initState() {
    super.initState();
    _subscription = _controller.stream.listen((data) {
      setState(() {
        _latest = data;
      });
    });
    // Simulate incoming data
    Future.delayed(Duration(seconds: 1), () {
      _controller.add("Hello from Stream!");
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('StreamSubscription Example')),
      body: Center(child: Text(_latest, style: TextStyle(fontSize: 24))),
    );
  }

  @override
  void dispose() {
    _subscription?.cancel();
    _controller.close();
    super.dispose();
  }
}

Note

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 2