Dart: Stream Transformation Issue with Custom StreamTransformer on Flutter Web
I'm getting frustrated with I've been struggling with this for a few days now and could really use some help. I'm working on a Flutter web application where I'm trying to implement a custom `StreamTransformer` to modify the data coming from a WebSocket connection. The transformer is designed to filter messages based on a specific condition and transform the output accordingly. However, I keep encountering a `Bad state: Stream already listened to` error when I try to listen to the transformed stream after applying the transformer. I've tried using the `asBroadcastStream()` method, but it doesn't seem to resolve the issue. Here's the code I have for the transformer: ```dart class MessageTransformer extends StreamTransformerBase<String, String> { @override Stream<String> bind(Stream<String> stream) { return stream.where((message) => message.contains('important')).map((message) { // Simulate some transformation return message.toUpperCase(); }); } } ``` And here is how I'm using it in my widget: ```dart class MessageWidget extends StatefulWidget { @override _MessageWidgetState createState() => _MessageWidgetState(); } class _MessageWidgetState extends State<MessageWidget> { late Stream<String> _messageStream; @override void initState() { super.initState(); final controller = StreamController<String>(); _messageStream = controller.stream.transform(MessageTransformer()).asBroadcastStream(); // Simulate incoming messages Future.delayed(Duration(seconds: 1), () { controller.add('This is an important message'); controller.add('Just a regular message'); controller.add('Another important one'); }); } @override Widget build(BuildContext context) { return StreamBuilder<String>( stream: _messageStream, builder: (context, snapshot) { if (snapshot.connectionState == ConnectionState.waiting) { return CircularProgressIndicator(); } else if (snapshot.hasError) { return Text('Error: ${snapshot.error}'); } else if (snapshot.hasData) { return Text('Received: ${snapshot.data}'); } return Text('No data'); }, ); } } ``` The error only happens when I try to listen to `_messageStream` multiple times in different widgets. I thought using `asBroadcastStream()` would allow multiple listeners, but it seems I'm still hitting a limitation. What could I be missing here? I'm using Dart SDK 2.15.1 and Flutter 2.10.0. I recently upgraded to Dart LTS. Has anyone else encountered this? I'm using Dart 3.11 in this project. Thanks for taking the time to read this! What's the correct way to implement this?