Exit an infinite stream-CodePudding

I've written this piece of code in order to scan Bluetooth devices in my Flutter app with the help of flutter_blue package.

Stream<List<ScanResult>> scannedDevices(int durationSeconds) async* {
  Stream<List<ScanResult>> stream = _flutterBlue.scanResults;
  List<ScanResult> payload = List<ScanResult>.empty(growable: true);

  _flutterBlue.startScan(timeout: Duration(seconds: durationSeconds));

  await for (List<ScanResult> results in stream) {
    payload.clear();
    for (ScanResult result in results) {
      payload.add(result);
    }
    yield payload;
}

The problem is that scanResults Stream is infitnite (see here) and because of that the await for loop runs foreverer, leaving my scannedDevices Stream running forever too.

Is there a way to break the await for loop after scanDuration has passed? Thanks

CodePudding user response：

Simply add an timeout to the stream that you are listening.

Another option is to use the StreamTransformer instead of what you did with await for.

Stream<List<ScanResult>> scannedDevices(int durationSeconds) async* {
  Stream<List<ScanResult>> stream = _flutterBlue.scanResults.timeout(Duration(seconds: durationSeconds));
  List<ScanResult> payload = List<ScanResult>.empty(growable: true);

  _flutterBlue.startScan(timeout: Duration(seconds: durationSeconds));

  await for (List<ScanResult> results in stream) {
      payload.clear();
      for (ScanResult result in results) {
        payload.add(result);
      }
      yield payload;
  }
}

CodePudding user response：

Yes, you can simply return null for breaking loop

 Stream<List<ScanResult>> scannedDevices(int durationSeconds) 
  async* {
    Stream<List<ScanResult>> stream = _flutterBlue.scanResults;
     List<ScanResult> payload = List<ScanResult>.empty(growable: 
       true);

     _flutterBlue.startScan(timeout: Duration(seconds: 
 durationSeconds));

 await for (List<ScanResult> results in stream) {
   payload.clear();
   for (ScanResult result in results) {
  payload.add(result);
 }
return payload;
}