Wait for stream inside a Future: Flutter

Question

I want to check if the Firebase DB is connected or not, so I have to use a Future to return a boolean

Have a check at my code..

@override
Future<bool> isAvailable() async {
 bool ret = false;
 await firebaseInstance.reference().child('.info/connected').onValue.listen((event) {
  ret =  event.snapshot.value;
});

return ret;
}

the firebaseInstace.reference is a StreamSubscription type and does not wait for the future to return me a result.

please help.

Have you tried my answer? – Peter Haddad Jun 12 '20 at 11:09 — Peter Haddad, Jun 12 '20 at 11:09

score 2 · Answer 1 · answered Jun 10 '20 at 14:11

2

If you only need to know the current value, use once().then instead of onValue.listen

@override
Future<bool> isAvailable() async {
  var snapshot = await firebaseInstance.reference().child('.info/connected').once();
  return snapshot.value;
}

answered Jun 10 '20 at 14:11

Frank van Puffelen

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scrimau · Answer 2 · 2020-06-10T18:27:12.200

1

Instead of awaiting the end of the stream subscription (it never ends), just take the first value:

@override
Future<bool> isAvailable() => firebaseInstance.reference().child('.info/connected').onValue.first;

edited Jun 10 '20 at 18:27

answered Jun 10 '20 at 13:08

scrimau

1,325
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You saved me! Thank you – Saman Apr 30 '21 at 14:24

score 0 · Answer 3 · answered Jun 10 '20 at 10:12

You can put the StreamSubcription in a variable

StreamSubscription subscription = someDOMElement.onSubmit.listen((data) {

   // you code here

   if (someCondition == true) {
     subscription.cancel();
   }

});

More can be found here is there any way to cancel a dart Future?

score 0 · Answer 4 · answered Jun 10 '20 at 12:30

You can do the following:

@override
  Future<bool> isAvailable() async {
    bool ret = false;
    Stream<Event> events =
        FirebaseDatabase.instance.reference().child('.info/connected').onValue;
    await for (var value in events) {
      ret = value.snapshot.value;
    }
    return ret;
  }

onValue returns a Stream<Event> and then you can use await for to iterate inside the Stream and get the data, and then it will return.

Wait for stream inside a Future: Flutter

4 Answers4