Flutter Blue Read Values from 2 Characteristics with notify

I'm a beginner in flutter and want to program a app with Bluetooth LE. I use flutter_blue. My App works if i only want to read the value of one characteristic. Now i need to read a second characteristic and that is the problem. I'm using a example from the esp32 dust sensor. The main is similar to the flutter blue example. The step to the next site is work with the following code:

             StreamBuilder<List<ScanResult>>(
            stream: FlutterBlue.instance.scanResults,
            initialData: [],
            builder: (c, snapshot) => Column(
              children: snapshot.data
                  .map(
                    (r) => ScanResultTile(
                  result: r,
                  onTap: () => Navigator.of(context)
                      .push(MaterialPageRoute(builder: (context) {
                    r.device.connect();
                    return SensorPage(device: r.device);
                  })),
                ),

That works ok. At the Sensor-Page there is the code for the Page which starts with:

@override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: _onWillPop,
      child: Scaffold(
        appBar: AppBar(
          title: Text(' Connect'),
        ),
        body: Container(
      //    color: Colors.purple,
          decoration: BoxDecoration(
            image: DecorationImage(
//              image: AssetImage("lib/Images/knaus.jpg"),
              image: AssetImage("lib/Images/innen.jpg"),
              fit: BoxFit.cover,
            ),
          ),

            child: !isReady
                ? Center(
                    child: Text(
                      "Warte auf Verbindung...",
                      style: TextStyle(fontSize: 24, color: Colors.red),
                    ),
                  )
                : Container(
                    child: StreamBuilder<List<int>>(
                      stream: wt_Ist_stream,
                      builder: (BuildContext context,
                          AsyncSnapshot<List<int>> snapshot) {
                        if (snapshot.hasError)
                          return Text('Error: ${snapshot.error}');
                        if (snapshot.connectionState ==
                            ConnectionState.active) {
                          _DataParser(snapshot.data);

The characteristics i generate with:

  List<BluetoothService> services = await widget.device.discoverServices();
    services.forEach((service) {
      if (service.uuid.toString() == SERVICE_UUID) {
        service.characteristics.forEach((characteristic) {
          if (characteristic.uuid.toString() == CHARACTERISTIC_UUID_WT_RcvWater) {
            characteristic.setNotifyValue(!characteristic.isNotifying);
            characteristic1=characteristic;
           // characteristic1.setNotifyValue(!characteristic.isNotifying);
            wt_Ist_stream = characteristic1.value;
         //   wt_Soll_stream = service.characteristic.value;
            setState(() {
              isReady = true;
            });
          }

          if (characteristic.uuid.toString() == CHARACTERISTIC_UUID_WT_Soll) {
            characteristic.setNotifyValue(!characteristic.isNotifying);
            characteristic2=characteristic;
//            characteristic2.setNotifyValue(!characteristic2.isNotifying);
            wt_Soll_stream = characteristic2.value;
        //    characteristic2.value.listen((InputString2)
                //   wt_Soll_stream = service.characteristic.value;
          }

          //Updating characteristic to perform write operation.
          if (characteristic.uuid.toString() == CHARACTERISTIC_UUID_WT_TxWater) {
            characteristic_Write=characteristic;
          }
        });
      }
    });

    if (!isReady) {
      _Pop();
    }
  }

Both reading-Characteristics are send Data to the app and i get the notification, that new data available [onCharacteristicChanged] uuid: 456e869c-d393-4cec-9f43-cef5382eab72]. but my Dataparser will only start if the value for uuid ...b72(wt_Ist_stream) changed. Then he gets the right string from snapshot.data.

If i changed the Streambuilder-Stream

  child: StreamBuilder<List<int>>(
                      stream: wt_Ist_stream,

to

  child: StreamBuilder<List<int>>(
                      stream: wt_Soll_stream,

my dataparser gets the value from characteristic 2. But how can i change my app that my parser starts automatic if one stream (wt_Ist_Stream or wt_Soll_stream) changed and then gets the right value.

The Streambuilder sends the right data to the dataparser but only the stream, which is called in stream:

How can i changed the code, that my parser starts on a stream-change and gets the right values from snapshot.data?

The dataparser-code:

_DataParser(List<int> dataFromDevice) {
    String InputString = utf8.decode(dataFromDevice);

    if (InputString.length>6) {.....}