Flutter_blue 和 Adafruit Bluefruit BLE 特征错误：找不到特征的 CCCD 描述符

问题描述

我目前遇到了我的 ble 项目的颤振问题。我正在使用 Paul Demarco 的 Flutter blue 包，该应用程序的附加页面基于来自 youtube 的“ThatProject”灰尘传感器。我有一个 Adafruit Feather 32u4 板，我试图通知客户端（我的 Flutter 应用程序）它有一系列数字要发送，但我没有得到任何输出。我能够连接到设备，并且似乎可以正确发送服务 UUID 和特征 UUID，但我不确定它是否具有正确的属性。 我正在使用 adafruit BLE 代码对电路板进行编程，如果我使用 adafruit 的应用程序，我可以获得这些值。我只是想在我自己的 Flutter 应用程序上获取值。

我遇到了如下错误：

E/Flutter (32139): [ERROR:Flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: PlatformException(set_notification_error,Could not locate CCCD descriptor for characteristic: 6e400002-b5a3-f393-e0a9-e50e24dcca9e,null,null)

这是我的代码。我相信缺少的 CCCD 来自这部分：

import 'dart:async';
import 'dart:convert' show utf8;

import 'package:Flutter/material.dart';
import 'package:Flutter_blue/Flutter_blue.dart';
import 'package:oscilloscope/oscilloscope.dart';

class SensorPage extends StatefulWidget {
  const SensorPage({Key key,this.device}) : super(key: key);
  final BluetoothDevice device;

  @override
  _SensorPageState createState() => _SensorPageState();
}

class _SensorPageState extends State<SensorPage> {
  final String SERVICE_UUID = "6e400001-b5a3-f393-e0a9-e50e24dcca9e";
  final String CHaraCTERISTIC_UUID = "6e400002-b5a3-f393-e0a9-e50e24dcca9e";
  bool isReady;
  Stream<List<int>> stream;
  List<double> traceDust = List();

  @override
  void initState() {
    super.initState();
    isReady = false;
    connectToDevice();
  }

  connectToDevice() async {
    // if (widget.device == null) {
    //   // _Pop();
    //   return;
    // }

    //timeout timer,watchdog timer if you will
    new Timer(const Duration(seconds: 15),() {
      if (!isReady) {
        disconnectFromDevice();
        //   _Pop();
      }
    });

    await widget.device.connect();
    discoverServices();
  }

  disconnectFromDevice() {
    if (widget.device == null) {
      //_Pop();
      return;
    }

    widget.device.disconnect();
  }

  discoverServices() async {
    // if (widget.device == null) {
    //   //  _Pop();
    //   return;
    // }

    BluetoothCharacteristic ss;
    List<BluetoothService> services = await widget.device.discoverServices();
    services.forEach((service) {
      debugPrint("This Service UUID is!${service.uuid.toString()}");
      if (service.uuid.toString() == SERVICE_UUID) {
        service.characteristics.forEach((characteristic) {
          debugPrint("This char UUID is!${characteristic.uuid.toString()}");
          if (characteristic.uuid.toString() == CHaraCTERISTIC_UUID) {
            debugPrint("Here is !isnotifying: ${!characteristic.isnotifying}");
            debugPrint("Here is characteristic.value: ${characteristic.value}");
            ss = characteristic;
            stream = ss.value;
            setState(() {
              isReady = true;
            });
          } //this one
        });
      } //this one
    });
    await ss.setNotifyValue(true);
    stream = ss.value;
    if (!isReady) {
      // _Pop();
    }
  }

  Future<bool> _onWillPop() {
    return showDialog(
        context: context,builder: (context) =>
            new AlertDialog(
              title: Text('Are you sure?'),content: Text('Do you want to disconnect device and go back?'),actions: <Widget>[
                new FlatButton(
                    onpressed: () => Navigator.of(context).pop(false),child: new Text('No')),new FlatButton(
                    onpressed: () {
                      disconnectFromDevice();
                      Navigator.of(context).pop(true);
                    },child: new Text('Yes')),],) ??
            false);
  }

  // _Pop() {
  //   Navigator.of(context).pop(true);
  // }

  String _dataParser(List<int> dataFromDevice) {
    debugPrint("current value is-> ${utf8.decode(dataFromDevice)}");
    return utf8.decode(dataFromDevice);
  }

  @override
  Widget build(BuildContext context) {
    Oscilloscope oscilloscope = Oscilloscope(
      showYAxis: true,padding: 0.0,backgroundColor: Colors.black,traceColor: Colors.white,yAxisMax: 3000.0,yAxisMin: 0.0,dataSet: traceDust,);

    return WillPopScope(
      onWillPop: _onWillPop,child: Scaffold(
        appBar: AppBar(
          title: Text('Optical Dust Sensor'),),body: Container(
            child: !isReady
                ? Center(
                    child: Text(
                      "Waiting...",style: TextStyle(fontSize: 24,color: Colors.red),)
                : Container(
                    child: StreamBuilder<List<int>>(
                      stream: stream,builder: (BuildContext context,AsyncSnapshot<List<int>> snapshot) {
                        if (snapshot.hasError)
                          return Text('Error: ${snapshot.error}');

                        if (snapshot.connectionState ==
                            ConnectionState.active) {
                          debugPrint("snapshot.error: ${snapshot.error}.");
                          debugPrint("snapshot.data: ${snapshot.error}.");
                          debugPrint(
                              "snapshot.connectionState: ${snapshot.connectionState}.");
                          debugPrint("snapshot.hasdata?: ${snapshot.hasData}.");

                          var currentValue = _dataParser(snapshot.data);
                          traceDust.add(double.tryParse(currentValue) ?? 0);

                          return Center(
                              child: Column(
                            mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[
                              Expanded(
                                flex: 1,child: Column(
                                    mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[
                                      Text('Current value from Sensor',style: TextStyle(fontSize: 14)),Text('$currentValue ug/m3',style: TextStyle(
                                              fontWeight: FontWeight.bold,fontSize: 24))
                                    ]),Expanded(
                                flex: 1,child: oscilloscope,)
                            ],));
                        } else {
                          return Text('Check the stream');
                        }
                      },)),);
  }
}

// copyright 2017,Paul Demarco.
// All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';

import 'package:Flutter/material.dart';
import 'package:K9Harness/Pages/Sensor_page.dart';
import 'package:K9Harness/Bluetooth/widgets.dart';
import 'package:Flutter_blue/Flutter_blue.dart';

class MyBluetoothPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,color: Colors.lightBlue,home: StreamBuilder<BluetoothState>(
          stream: FlutterBlue.instance.state,initialData: BluetoothState.unkNown,builder: (c,snapshot) {
            final state = snapshot.data;
            if (state == BluetoothState.on) {
              return FindDevicesScreen();
            }
            return BluetoothOffScreen(state: state);
          }),);
  }
}

class BluetoothOffScreen extends StatelessWidget {
  const BluetoothOffScreen({Key key,this.state}) : super(key: key);

  final BluetoothState state;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.lightBlue,body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,children: <Widget>[
            Icon(
              Icons.bluetooth_disabled,size: 200.0,color: Colors.white54,Text(
              'Bluetooth Adapter is ${state.toString().substring(15)}.',style: Theme.of(context)
                  .primaryTextTheme
                  .subhead
                  .copyWith(color: Colors.white),);
  }
}

class FindDevicesScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Find Devices'),body: Refreshindicator(
        onRefresh: () => FlutterBlue.instance
            .startScan(
                scanMode: ScanMode.balanced,withServices: [
                  Guid("6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
                ],//FIXME check the other ways where ".startScan" is implemented
                timeout: Duration(seconds: 4))
            .catchError((error) {
          print("error starting scan $error");
        }),child: SingleChildScrollView(
          child: Column(
            children: <Widget>[
              StreamBuilder<List<BluetoothDevice>>(
                stream: Stream.periodic(Duration(seconds: 2))
                    .asyncMap((_) => FlutterBlue.instance.connectedDevices),initialData: [],snapshot) => Column(
                  children: snapshot.data
                      .map((d) => ListTile(
                            title: Text(d.name),subtitle: Text(d.id.toString()),trailing: StreamBuilder<BluetoothDeviceState>(
                              stream: d.state,initialData: BluetoothDeviceState.disconnected,snapshot) {
                                if (snapshot.data ==
                                    BluetoothDeviceState.connected) {
                                  return RaisedButton(
                                    child: Text('OPEN'),onpressed: () => Navigator.of(context).push(
                                        MaterialPageRoute(
                                            builder: (context) =>
                                                DeviceScreen(device: d))),);
                                }
                                return Text(snapshot.data.toString());
                              },))
                      .toList(),StreamBuilder<List<ScanResult>>(
                stream: FlutterBlue.instance.scanResults,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);
                          })),)
                      .toList(),floatingActionButton: StreamBuilder<bool>(
        stream: FlutterBlue.instance.isScanning,initialData: false,snapshot) {
          if (snapshot.data) {
            return FloatingActionButton(
              child: Icon(Icons.stop),onpressed: () => FlutterBlue.instance.stopScan(),backgroundColor: Colors.red,);
          } else {
            return FloatingActionButton(
                child: Icon(Icons.search),onpressed: () => FlutterBlue.instance
                        .startScan(
                            scanMode: ScanMode.balanced,withServices: [
                              Guid("6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
                            ],//FIXME check the other ways where ".startScan" is implemented
                            timeout: Duration(seconds: 4))
                        .catchError((error) {
                      print("error starting scan $error");
                    }));
          }
        },);
  }
}

class DeviceScreen extends StatelessWidget {
  const DeviceScreen({Key key,this.device}) : super(key: key);

  final BluetoothDevice device;

  List<Widget> _buildServiceTiles(List<BluetoothService> services) {
    return services
        .map(
          (s) => ServiceTile(
            service: s,characteristicTiles: s.characteristics
                .map(
                  (c) => CharacteristicTile(
                    characteristic: c,onReadpressed: () => c.read(),onWritepressed: () => c.write([13,24]),onNotificationpressed: () =>
                        c.setNotifyValue(!c.isnotifying),descriptorTiles: c.descriptors
                        .map(
                          (d) => DescriptorTile(
                            descriptor: d,onReadpressed: () => d.read(),onWritepressed: () => d.write([11,12]),)
                        .toList(),)
                .toList(),)
        .toList();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(device.name),actions: <Widget>[
          StreamBuilder<BluetoothDeviceState>(
            stream: device.state,initialData: BluetoothDeviceState.connecting,snapshot) {
              VoidCallback onpressed;
              String text;
              switch (snapshot.data) {
                case BluetoothDeviceState.connected:
                  onpressed = () => device.disconnect();
                  text = 'disCONNECT';
                  break;
                case BluetoothDeviceState.disconnected:
                  onpressed = () => device.connect();
                  text = 'CONNECT';
                  break;
                default:
                  onpressed = null;
                  text = snapshot.data.toString().substring(21).toupperCase();
                  break;
              }
              return FlatButton(
                  onpressed: onpressed,child: Text(
                    text,style: Theme.of(context)
                        .primaryTextTheme
                        .button
                        .copyWith(color: Colors.white),));
            },)
        ],body: SingleChildScrollView(
        child: Column(
          children: <Widget>[
            StreamBuilder<BluetoothDeviceState>(
              stream: device.state,snapshot) => ListTile(
                leading: (snapshot.data == BluetoothDeviceState.connected)
                    ? Icon(Icons.bluetooth_connected)
                    : Icon(Icons.bluetooth_disabled),title: Text(
                    'Device is ${snapshot.data.toString().split('.')[1]}.'),subtitle: Text('${device.id}'),trailing: StreamBuilder<bool>(
                  stream: device.isdiscoveringServices,snapshot) => IndexedStack(
                    index: snapshot.data ? 1 : 0,children: <Widget>[
                      IconButton(
                        icon: Icon(Icons.refresh),onpressed: () => device.discoverServices(),IconButton(
                        icon: SizedBox(
                          child: CircularProgressIndicator(
                            valueColor: AlwaysstoppedAnimation(Colors.grey),width: 18.0,height: 18.0,onpressed: null,)
                    ],StreamBuilder<int>(
              stream: device.mtu,initialData: 0,snapshot) => ListTile(
                title: Text('MTU Size'),subtitle: Text('${snapshot.data} bytes'),trailing: IconButton(
                  icon: Icon(Icons.edit),onpressed: () => device.requestMtu(223),StreamBuilder<List<BluetoothService>>(
              stream: device.services,snapshot) {
                return Column(
                  children: _buildServiceTiles(snapshot.data),);
              },);
  }
}

解决方法

我想通了，我的特征 UUID 是“6e400002-b5a3-f393-e0a9-e50e24dcca9e”，它应该是“6e400003-b5a3-f393-e0a9-e50e24dcca9e”，因为通知通知特性必须是 0x0003 而不是 2。然后当我改变这个值时它正确地通过了 CCCD。