[Help]: Should iOS automatically stop the scan when the bluetooth adapter is turned off?

[decaf-dev]

FlutterBluePlus Version

1.15.8

Flutter Version

3.13.2

What OS?

iOS

OS Version

16.6

Bluetooth Module

Not sure

Ask your question

What should be the expected behavior when the bluetooth adapter is turned off on iOS. Right now it seems if a user had a scan running before the adapter was turned off, the scan is still running. However, it no longer produces scan results.

Steps to reproduce:

1. Start a scan
2. Turn off the bluetooth adapter
3. Turn on the bluetooth adapter
4. There's no exception but no scan results are coming in now

The logs are for when I don't try starting a new scan.

I am using the scanning extension from the migration file

  Stream<ScanResult> _scan({
    List<Guid> withServices = const [],
    Duration? timeout,
    bool androidUsesFineLocation = false,
  }) {
    if (FlutterBluePlus.isScanningNow) {
      throw Exception("Another scan is already in progress");
    }

    final controller = StreamController<ScanResult>();

    var subscription = FlutterBluePlus.scanResults.listen(
      (r) => controller.add(r.first),
      onError: (e, stackTrace) => controller.addError(e, stackTrace),
    );

    FlutterBluePlus.startScan(
      withServices: withServices,
      timeout: timeout,
      removeIfGone: null,
      oneByOne: true,
      androidUsesFineLocation: androidUsesFineLocation,
    );

    Future scanComplete =
        FlutterBluePlus.isScanning.where((e) => e == false).first;

    scanComplete.whenComplete(() {
      subscription.cancel();
      controller.close();
    });

    return controller.stream;
  }

If I try starting a scan, I get an error. This indicates that for sure, the scan is running
Steps to reproduce:

1. Start a scan
2. Turn off the bluetooth adapter
3. Turn on the bluetooth adapter
4. Try starting a new scan
5. See exception

Logs

[FBP-iOS] centralManagerDidUpdateState CBManagerStatePoweredOff
[FBP-iOS] disconnectAllDevices
[FBP-iOS] calling disconnect: XXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXXX
[CoreBluetooth] API MISUSE: <CBCentralManager: 0x2827fdae0> can only accept this command while in the powered on state
flutter: [app] BluetoothStackState.init.: adapterState: BluetoothAdapterState.off
[FBP-iOS] centralManagerDidUpdateState CBManagerStatePoweredOn
flutter: [oh_ble] BluetoothStackState.init.: adapterState: BluetoothAdapterState.on

Nothing happens even though it's still scanning

[chipweinberger]

If I try starting a scan, I get an error.

What error do you get?

and yes, we should automatically stop the scan

[chipweinberger]

Also, feel free to try and fix this yourself, and open a PR.

For one, we should listen to OnAdapterStateChanged in _methodCallHandler

  static Future<dynamic> _methodCallHandler(MethodCall call) async {

    // keep track of adapter states
    if (call.method == "OnAdapterStateChanged") {
        BmBluetoothAdapterState r = BmBluetoothAdapterState.fromMap(call.arguments);
        if(isScanningNow && r.adapterState != BmAdapterStateEnum.on ) {
            _scanSubscription?.cancel();
            _scanTimeout?.cancel();
            _isScanning.add(false);
        }
    }

But I am not sure if there needs to be any changes to the iOS code. I'm curious what error you are getting.

[decaf-dev]

Here is the error that I am getting. It is originating from the migration code. Once the bluetooth adapter stream changes to on, I call scan function from the migration guide. I have named it to _scan.

(I have modified the code a little bit to show case the behavior I'm getting. The overall stacktrace is irrelevant)

══╡ EXCEPTION CAUGHT BY FOUNDATION LIBRARY ╞════════════════════════════════════════════════════════
The following _Exception was thrown while dispatching notifications for ValueNotifier<BTState>:
Exception: Another scan is already in progress

When the exception was thrown, this was the stack:
#0      BTDeviceScanner._scan (package:app/bt_device_scanner.dart:166:7)
#1      BTDeviceScanner.scanBTDevicesByMacAddress (package:app/bt_device_scanner.dart:133:14)
#2      BluetoothService.startScan (package:app/services/bluetooth_service.dart:137:49)
#3      BluetoothService._btStateListener (package:app/services/bluetooth_service.dart:70:9)
#4      ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:403:24)
#5      ValueNotifier.value= (package:flutter/src/foundation/change_notifier.dart:530:5)
#6      BluetoothStackState.init.<anonymous closure> (package:app/bluetooth_stack_state.dart:67:23)
(elided 17 frames from dart:async)

The ValueNotifier<BTState> sending notification was:
  ValueNotifier<BTState>#9ab2c(BTState.on)
════════════════════════════════════════════════════════════════════════════════════════════════════

    btStateSubscription = FlutterBluePlus.adapterState.listen((state) async {
      if (state ==  BluetoothAdapterState.on){
         if (_isBTServiceOff){
            _isBTServiceOff = false;
           _scan();
     } else if ( state == BluetoothAdapterState.off){
        _isBTServiceOff = true;
      }
    });

Logs

[FBP-iOS] didUpdateValueForCharacteristic XXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXXX
[FBP-iOS] centralManagerDidUpdateState CBManagerStatePoweredOff
[FBP-iOS] disconnectAllDevices
[FBP-iOS] calling disconnect: XXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXXX
[FBP-iOS] centralManagerDidUpdateState CBManagerStatePoweredOn

[chipweinberger]

Another scan is already in progress

Oh ok, great. The code change I suggested above will fix this.

[decaf-dev]

Just tested it. Yep! That fixes it.

[chipweinberger]

ok, I pushed a fix to master branch. please try it!

I will do a release tomorrow, if master branch works for you.

[chipweinberger]

fixed 1.15.9