Dart flutter stream stop and start with condition?

Question

I want to stop and restart a stream conditionally, how can I do that?

_fireStore
.collection(...)
.doc(...)
.snapshots().takeWhile((element) => _listenable);

Stream stops when _listenable is false but doesn't restart when true ?

Anyone know how to do it?

Answer 1

You can use async to easily control the stream This is how you can do it.

First create a StreamSubsctiprion like this

StreamSubscription<QuerySnapshot>? _eventStream;

and then set a listener for your snapshots stream.

here is how you can store stream query snapshot

 Stream<QuerySnapshot> streamSub =_fireStore
    .collection(...)
    .doc(...)
    .snapshots();

add listener for your stream like this

   _eventStream = streamSub.listen((snapshot) => _eventStream);

Then you can use your event stream to cancel, pause and resume your stream like this

 _eventStream!.pause();
 _eventStream!.cancel();
 _eventStream!.resume();

here is my final code

class MainScreen extends State<PaymentScreen> {
  StreamSubscription<QuerySnapshot>? _eventStream;

  @override
  Widget build(BuildContext context) {
    Stream<QuerySnapshot> myStream = FirebaseFirestore.instance.collection('Users').snapshots();
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 20),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.end,
          children: [
            StreamBuilder<QuerySnapshot>(
              stream: myStream,
              builder: (BuildContext context,
                  AsyncSnapshot<QuerySnapshot> snapshot) {
                if (snapshot.hasError) {
                  return Text('Something went wrong');
                }

                if (snapshot.connectionState == ConnectionState.waiting) {
                  return Text("Loading");
                }

                return Column(
                  children:
                      snapshot.data!.docs.map((DocumentSnapshot document) {
                    Map<String, dynamic> data =
                        document.data()! as Map<String, dynamic>;
                    return ListTile(
                      title: Text(data['firstName']),
                    );
                  }).toList(),
                );
              },
            ),
            FloatingActionButton.extended(
              onPressed: () {
                _eventStream = myStream.listen((snapshot) => _eventStream);
                try {
                  _eventStream!.pause();
                  print('paused');
                } catch (e, s) {
                  print(s);
                }
              },
              label: const Text("Pause Stream"),
            ),
          ],
        ),
      ),
    );
  }
}