I’m developing a Flutter application where I need to connect and pair a Bluetooth Low Energy (BLE) device with a phone. I’m using the flutter_blue package for Bluetooth connectivity. While I can scan for devices and connect to them, I’m struggling with how to handle the pairing process.

Here’s a snippet of my code for scanning and connecting to devices:

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

class BluetoothLEManager extends StatefulWidget {
  const BluetoothLEManager({Key? key}) : super(key: key);

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

class BluetoothLEManagerState extends State<BluetoothLEManager> with SingleTickerProviderStateMixin {
  FlutterBlue flutterBlue = FlutterBlue.instance;
  List<BluetoothDevice> _devices = [];
  bool _isSearching = false;
  bool _scanCompleted = false;

  @override
  void initState() {
    super.initState();
    startBluetoothScan(isInitialScan: true);
  }

  @override
  void dispose() {
    flutterBlue.stopScan();
    super.dispose();
  }

  void startBluetoothScan({bool isInitialScan = false}) {
    if (_isSearching) return;

    setState(() {
      _isSearching = true;
      _scanCompleted = false;
    });

    flutterBlue.startScan(timeout: const Duration(seconds: 10)).then((_) {
      setState(() {
        _isSearching = false;
        _scanCompleted = true;
      });
    });

    flutterBlue.scanResults.listen((results) {
      setState(() {
        _devices = results.map((r) => r.device).where((device) => device.name.isNotEmpty).toList();
      });
    });

    flutterBlue.isScanning.listen((isScanning) {
      if (!isScanning) {
        print('Scanning stopped');
      }
    });
  }

  Future<void> connectToDevice(BluetoothDevice device) async {
    await device.connect();
    // further code to handle connection and service discovery
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BLE Devices'),
      ),
      body: ListView.builder(
        itemCount: _devices.length,
        itemBuilder: (context, index) {
          return ListTile(
            title: Text(_devices[index].name),
            onTap: () => connectToDevice(_devices[index]),
          );
        },
      ),
    );
  }
}

How do I pair a BLE device with the phone using the flutter_blue package and is there a specific method or process I should follow to ensure the device is paired before establishing a connection?

Any guidance or example code would be greatly appreciated.

(What I’ve tried below)

Attempt to Check Bond State and Pair:

I tried to check the bond state of the device and initiate pairing if the device was not already paired. The code snippet I used was:

Future<void> checkAndPairDevice(BluetoothDevice device) async {
  final BondState bondState = await device.bondState.first;

  if (bondState == BondState.bonded) {
    print('Device is already paired');
  } else {
    print('Device is not paired. Attempting to pair...');
    try {
      await device.pair();
      print('Pairing successful');
    } catch (error) {
      print('Pairing failed: $error');
      return;
    }
  }
}

Unfortunately, this approach did not work because the flutter_blue package does not support the bondState and pair methods directly. I encountered errors indicating these methods were undefined.

Switching to flutter_blue_plus Package:

I attempted to switch to the flutter_blue_plus package, which has more features and active maintenance. However, this resulted in numerous type conflicts and compatibility issues between flutter_blue and flutter_blue_plus types, making it impractical to integrate both packages.

Manual Pairing:

I also considered manually prompting the user to pair the devices via the system’s Bluetooth settings before initiating the connection in the app. However, this approach does not provide a seamless user experience and does not ensure the app can programmatically verify and handle pairing.