Flutter how to listen to websocket response?

Make sure you are closing your WebSocket connection when you leave the current widget. Inside your widget's State class you should have a dispose() method that looks like this:

@overridevoid dispose() {  widget.channel.sink.close();  super.dispose();}

What I am want is an async function which receives every websocket response and append the result to a list, so that the listview can be updated.

You need to manage this yourself in your state class.

final list = List<Message>();@overrideWidget build(BuildContext context) {  return new StreamBuilder(    stream: myStream,    builder: (context, snapshot) {      list.add(/* extract message from snapshot */);      /* build a widget with your list */    },  );}

when enter that page again, there was an error says Bad state: Stream has already been listened to.. How to make the stream can be listened at every begaining, and then boradcast to many pages?

Dart has two kinds of streams, single-subscription and broadcast streams. See more info about the differences, and how to create streams. Recommendations here will depend largely on your application.

That said, usually apis that return a stream default to single-subscription and then have the asBroadcastStream() alternative.

If that's not an option, you can create an intermediate StreamController that listens on your single-subscription stream and returns a broadcast stream, that the rest of your app should listen to.

Both of these options are outlined in the link above about creating streams.