Flutter“字符串”不是“列表”类型的子类型<int> '</int>

Question

I am trying to subscribe to my BLE device characteristic and print the notified values on my phones screen. I know the code is horrible, but this is my first flutter project so bear with me please.

The error comes from the StreamBuilder widget and the problem should be utf8.decode(snapshot.data)

I would also happily accept any ideas on how to make the code easier to read and more efficient, since this right here for the moment is the best I can do.

FlutterBlue flutterBlue = FlutterBlue.instance;
BluetoothDevice device;
BluetoothState state;
BluetoothDeviceState deviceState;

StreamSubscription<ScanResult> subscription;
var myUUID = "11111815-0000-1000-8000-00805f9b34fb";
var myCharacteristicUUID = "00002aca-0000-1000-8000-00805f9b34fb";
var myDevice = "ESP32";
var currentValue;

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}
 
class _MyHomePageState extends State<MyHomePage> {
      void scanForDevices() async {
        if (flutterBlue.isScanning != null) {
          print("Scanning");
          subscription = flutterBlue
              .scan(timeout: const Duration(seconds: 4))
              .listen((scanResult) async {
            if (scanResult.device.name == myDevice) {
              print("found ESP32");
              //Assigning bluetooth device
              device = scanResult.device;
              //After that we stop the scanning for device
              stopScanning();
            }
          });
        } else {
          print("Already scanning");
        }
        print("Scan stopped");
      }
    
      void stopScanning() {
        flutterBlue.stopScan();
        subscription.cancel();
        connectToDevice();
      }
    
      connectToDevice() async {
    //flutter_blue makes our life easier
        await device.connect();
        print("ESP32 connected");
    //After connection start dicovering services
        discoverServices();
      }
    
      BluetoothCharacteristic c;
    //This stream is for taking characteristic's value
    //for reading data provided by device
      Stream<List<int>> listStream;
      discoverServices() async {
        print("Discovering services");
        List<BluetoothService> services = await device.discoverServices();
        //checking each services provided by device
        services.forEach((service) {
          if (service.uuid.toString() == myUUID) {
            service.characteristics.forEach((characteristic) async {
              if (characteristic.uuid.toString() == myCharacteristicUUID) {
                //Updating stream to perform read operation.
                listStream = characteristic.value;
                await characteristic.setNotifyValue(!characteristic.isNotifying);
                characteristic.value.listen((value) {
                  print(utf8.decode(value));
                });
              }
            });
          }
        });
      }
    
      @override
      Widget build(BuildContext context) {
    
        return Scaffold(
          appBar: AppBar(
            title: Text(widget.title),
          ),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text("Stream:"),
                StreamBuilder(
                  stream: listStream,
                  initialData: "None",
                  builder: (context, snapshot) {
                    // if i remove "utf8.decode(snapshot.data)" the error goes away
                    return Text(utf8.decode(snapshot.data));
                  },
                ),
              ],
            ),
          ),
          floatingActionButton: FloatingActionButton(
            onPressed: scanForDevices,
            tooltip: 'Scan',
            child: Icon(Icons.add),
          ), // This trailing comma makes auto-formatting nicer for build methods.
        );
      }
    }

Answer 1

It seems you are trying to pass String value into a List having Integer format. Change the List type from Integer to String. This could solve the issue.