flutter_bluetooth_serial库自动调用cancelDiscovery()问题求助

开发Flutter蓝牙应用时，使用flutter_bluetooth_serial包（版本0.4.0），在initState中调用startDiscovery()后，cancelDiscovery会被无理由立即触发。前两三次运行正常，之后出现如下日志：

D/BluetoothAdapter(15019): startDiscovery(): called by: com.example.bluetooth_app
D/FlutterBluePlugin(15019): Canceling discovery (stream closed)
D/BluetoothAdapter(15019): cancelDiscovery(): called by: com.example.bluetooth_app

使用Flutter版本3.7，完整代码如下：

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_bluetooth_serial/flutter_bluetooth_serial.dart';

class FooPage extends StatefulWidget {
  const FooPage({super.key});

  @override
  State<FooPage> createState() => _FooPageState();
}

class _FooPageState extends State<FooPage> {
  List<BluetoothDiscoveryResult> devices = [];

  late StreamSubscription<BluetoothDiscoveryResult>
      _discoveryStreamSubscription;

  @override
  void initState() {
    super.initState();
    _startDiscovery();
  }

  void _startDiscovery() {
    _discoveryStreamSubscription =
        FlutterBluetoothSerial.instance.startDiscovery().listen(
      (r) {
        print('device found');
        bool deviceFound = false;
        devices.forEach((element) {
          if (element.device.address == r.device.address) {
            deviceFound = true;
          }
        });
        if (!deviceFound) {
          setState(() {
            devices.add(r);
          });
        }
      },
    );

    _discoveryStreamSubscription.onDone(() {
      setState(() {
        print('stream closed');
        // _isDiscovering = false;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    print(devices);
    return Scaffold(
      appBar: AppBar(
        title: Text("Bluetooth Devices"),
      ),
      body: devices.length == 0
          ? Center(
              child: Text('No Nearby devices can be found currently...'),
            )
          : ListView(
              children: devices
                  .map(
                    (e) => ListTile(
                      title: Text(e.device.name!),
                      subtitle: Text(e.device.type.stringValue),
                    ),
                  )
                  .toList(),
            ),
    );
  }
}

1. 清理StreamSubscription生命周期 #

当前代码未在页面销毁时取消订阅，多次进入页面会残留旧订阅干扰新发现流程，需在dispose中添加取消逻辑：

@override
void dispose() {
  _discoveryStreamSubscription.cancel();
  super.dispose();
}

2. 启动发现前先终止已有任务 #

系统同一时间只能运行一个蓝牙发现任务，启动新发现前先调用cancelDiscovery()确保无残留进程：

void _startDiscovery() async {
  // 先终止正在进行的发现
  await FlutterBluetoothSerial.instance.cancelDiscovery();
  
  _discoveryStreamSubscription =
      FlutterBluetoothSerial.instance.startDiscovery().listen(
    (r) {
      print('device found');
      bool deviceFound = false;
      devices.forEach((element) {
        if (element.device.address == r.device.address) {
          deviceFound = true;
        }
      });
      if (!deviceFound) {
        setState(() {
          devices.add(r);
        });
      }
    },
  );

  _discoveryStreamSubscription.onDone(() {
    setState(() {
      print('stream closed');
      // _isDiscovering = false;
    });
  });
}

3. 确认蓝牙权限配置 #

Android 12+需要额外的BLUETOOTH_SCAN和BLUETOOTH_CONNECT权限，确保在AndroidManifest.xml中声明：

<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

同时需在运行时请求这些权限，可借助permission_handler包实现权限申请逻辑。

4. 避免重复触发发现 #

页面重建（如屏幕旋转）会再次调用initState，导致重复启动发现任务，可添加状态变量控制：

bool _isDiscovering = false;

void _startDiscovery() async {
  if (_isDiscovering) return;
  
  setState(() => _isDiscovering = true);
  await FlutterBluetoothSerial.instance.cancelDiscovery();
  
  _discoveryStreamSubscription =
      FlutterBluetoothSerial.instance.startDiscovery().listen(
    (r) {
      // 原有设备处理逻辑
    },
    onDone: () {
      setState(() {
        _isDiscovering = false;
        print('stream closed');
      });
    },
  );
}

内容的提问来源于stack exchange，提问作者Programmerz