How can i make future function to wait for a stream to complete?

Question

Future notifyRead(Guid characteristic, BuildContext context) async {
    try {
      if (await FlutterBlue.instance.isOn) {
        BluetoothCharacteristic charToTarget = _characteristics
            .firstWhere((element) => element.uuid == characteristic);
        await charToTarget.setNotifyValue(true);
        clearInfo();
        var stream = charToTarget.value.listen(
          (value) {
            var temp = String.fromCharCodes(value);
            _info.add(temp);
            print(temp);
            notifyListeners();
            if (temp.startsWith("batt")) {
              updateBattValues(temp);
            }
            updateWifiVerificationStatus();

            if (_info.length == 17) {
              log("Finished Sending Data ");
              _notifyFinished = true;
              notifyListeners();
              return;
            }
          },
        );
        await charToTarget.write(INFO.codeUnits);
      } else {
        Fluttertoast.showToast(msg: "Seems like your Bluetooth is turned off");
      }
    } catch (e) {
      log("Some error occurred in retrieving info ${e.toString()}");
      Fluttertoast.showToast(
          msg: "Some error occurred in retrieving info ${e.toString()}");
    }
  }

I want this notifyRead method to wait for the stream inside to complete.But I am not able to achieve the same.The stream does not have an end associated with it , all I know is the stream outputs 17 values(that I save in _info array ) , so the check the length of the data and mark the end. This notifyRead method is called by a button's onTap.I want to show a till the stream finishes.

A stream is never meant to be "complete", it's always continuous. If you want something that gives a value and then stops, please use a future instead — sigmapie8, Mar 08 '23 at 07:38
@sigmapie8 streams can emit a "done" event at which point they will emit no further events. — Gregory Conrad, Mar 08 '23 at 20:38

score 1 · Accepted Answer · answered Mar 08 '23 at 08:00

This is very straightforward when using await for:

void main() async {
  print('before');
  await asyncFunction();
  print('after');
}

Future<void> asyncFunction() async {
  int count = 0;
  await for (var _ in streamFunction()) {
    count++;
    print('count = $count');
    if (count == 17) {
      break;
    }
  }
}

Stream<int> streamFunction() async* {
  for (var i = 0; ; i++) {
    yield i;
  }
}

Output:

before
count = 1
count = 2
count = 3
count = 4
count = 5
count = 6
count = 7
count = 8
count = 9
count = 10
count = 11
count = 12
count = 13
count = 14
count = 15
count = 16
count = 17
after

How can i make future function to wait for a stream to complete?

1 Answers1