flutter - BLE 模块问题 : Exception: Another scan is already in progress

Question

我正在尝试使以下操作成为可能:
我运行我的应用程序，当我按下“连接”按钮时，我连接到我的 BLE 模块。
第二个按钮允许我断开与它的连接。
问题是，如果我连接到 BLE 模块，然后按下断开按钮，它会断开连接，但我将无法再连接到 BLE(我必须重新启动应用程序)。
有我的代码:

import 'dart:async';
import 'dart:convert' show utf8;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_blue/flutter_blue.dart';

void main() {
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.landscapeRight,
    DeviceOrientation.landscapeLeft
  ]);
  runApp(MainScreen());
}

class MainScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'BLUETOOTH',
      debugShowCheckedModeBanner: false,
      home: Home(),
      theme: ThemeData.dark(),
    );
  }
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  String connectionText = "";
  final String SERVICE_UUID = "4fafc201-1fb5-459e-8fcc-c5c9c331914b";
  final String CHARACTERISTIC_UUID = "beb5483e-36e1-4688-b7f5-ea07361b26a8";
  final String TARGET_DEVICE_NAME = "MLT-BT05";
  FlutterBlue flutterBlue = FlutterBlue.instance; // * Instance de FlutterBlue
  StreamSubscription<ScanResult> scanSubScription; // * StreamSubscription
  BluetoothDevice targetDevice; // * Device
  BluetoothCharacteristic targetCharacteristic; // * Characteristiques

  @override
  void initState() {
    super.initState();
//    startScan();
  }

  startScan() {
    setState(() {
      connectionText = "Start Scanning";
    });

    scanSubScription = flutterBlue.scan().listen((scanResult) {
      print(scanResult.device.name.toString()); // ! TEST
      if (scanResult.device.name == TARGET_DEVICE_NAME) {
        print('DEVICE found');
        stopScan();
        setState(() {
          connectionText = "Found Target Device";
        });

        targetDevice = scanResult.device;
        connectToDevice();
      }
    }, onDone: () => stopScan());
  }

  stopScan() {
    scanSubScription?.cancel();
    scanSubScription = null;
  }

  connectToDevice() async {
    if (targetDevice == null) return;

    setState(() {
      connectionText = "Device Connecting";
    });

    await targetDevice.connect();
    print('DEVICE CONNECTED');
    setState(() {
      connectionText = "Device Connected";
    });

    discoverServices();
  }

  disconnectFromDevice() {
    if (targetDevice == null) return;

    targetDevice.disconnect();

    setState(() {
      connectionText = "Device Disconnected";
    });
  }

  discoverServices() async {
    if (targetDevice == null) return;

    List<BluetoothService> services = await targetDevice.discoverServices();
    services.forEach((service) {
      // do something with service
      if (service.uuid.toString() == SERVICE_UUID) {
        service.characteristics.forEach((characteristic) {
          if (characteristic.uuid.toString() == CHARACTERISTIC_UUID) {
            targetCharacteristic = characteristic;
            writeData("Hi there, ESP32!!");
            setState(() {
              connectionText = "All Ready with ${targetDevice.name}";
            });
          }
        });
      }
    });
  }

  writeData(String data) {
    if (targetCharacteristic == null) return;

    List<int> bytes = utf8.encode(data);
    targetCharacteristic.write(bytes);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(connectionText),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            FlatButton(
              child: Text("Connect"),
              color: Colors.grey[700],
              onPressed: () {
                startScan();
              },
            ),
            FlatButton(
              child: Text("Disconnect"),
              color: Colors.grey[700],
              onPressed: () {
                disconnectFromDevice();
              },
            ),
          ],
        ),
      ),
    );
  }
}

该错误告诉我，即使在连接设备后取消了 scanSubScription 并将其设置为 null，但另一次扫描已经在进行中。
错误:

I/flutter (13433): [TV] Samsung 7 Series (55)
I/flutter (13433): MLT-BT05
I/flutter (13433): DEVICE found
I/flutter (13433): DEVICE CONNECTED
E/flutter (13433): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: Exception: Another scan is already in progress.
E/flutter (13433): #0      FlutterBlue.scan (package:flutter_blue/src/flutter_blue.dart:81:7)
E/flutter (13433): <asynchronous suspension>
E/flutter (13433): #1      _HomeState.startScan (package:bluetoothv8/main.dart:53:36)
E/flutter (13433): #2      _HomeState.build.<anonymous closure> (package:bluetoothv8/main.dart:140:17)
E/flutter (13433): #3      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:706:14)
E/flutter (13433): #4      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:789:36)
E/flutter (13433): #5      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (13433): #6      TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:486:11)
E/flutter (13433): #7      BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:264:5)
E/flutter (13433): #8      BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:199:7)
E/flutter (13433): #9      PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:467:9)
E/flutter (13433): #10     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
E/flutter (13433): #11     PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:117:9)
E/flutter (13433): #12     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
E/flutter (13433): #13     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:115:18)
E/flutter (13433): #14     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:7)
E/flutter (13433): #15     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (13433): #16     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (13433): #17     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (13433): #18     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (13433): #19     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (13433): #20     _rootRunUnary (dart:async/zone.dart:1138:13)
E/flutter (13433): #21     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter (13433): #22     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter (13433): #23     _invoke1 (dart:ui/hooks.dart:273:10)
E/flutter (13433): #24     _dispatchPointerDataPacket (dart:ui/hooks.dart:182:5)

Answer 1

代替:

stopScan() {
    scanSubScription?.cancel();
    scanSubScription = null;
  }

写:

stopScan() {
    flutterBlue.stopScan();
    scanSubScription?.cancel();
    scanSubScription = null;
  }