退出无限流

Question

我编写了这段代码，以便在蓝色包的帮助下，在我的颤振应用程序中扫描蓝牙设备。

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;
}

问题是，scanResults流很受欢迎(请参阅这里)，因此await for循环将永远运行，而我的scannedDevices流也将永远运行。

是否有办法在await for通过后中断scanDuration循环？谢谢

Answer 1

是的，您只需返回null就可以中断循环。

 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;
}

Answer 2

只需向您正在侦听的流添加一个timeout即可。

另一种选择是使用StreamTransformer，而不是使用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;
  }
}