Windows BLE UWP disconnect - bluetooth-lowenergy

Question

How one forces Windows to disconnect from BLE device being used in UWP app? I receive notifications from some characteristics but at some point I want to stop receiving them and make sure I disconnect from the BLE device to save BLE device's battery?

Answer 1

Assuming your application is running as a gatt client and you have the following instances your are working with in your code:
GattCharacteristic myGattchar; // The gatt characteristic you are reading or writing on your BLE peripheral
GattDeviceService myGattServ; // The BLE peripheral' gatt service on which you are connecting from your application
BluetoothLEDevice myBleDev; // The BLE peripheral device your are connecting to from your application
When you are already connected to your BLE peripheral, if you call the Dispose() methods like this :
myBleDev.Dispose(); and/or myGattServ.Dispose(); and/or myGattchar.Service.Dispose()
you surely will free resources in your app but will not cleanly close the BLE connection: The application looses access to control resources for the connection. Nevertheless, connection remains established on the lower levels of the stack (On my peripheral device the Bluetooth connection active LED remains ON after calling any of Dispose() methods).
Forcing disconnection is done by first disabling notifications and indications on the concerned characteristic (i.e. myGattchar in my example above) by writing a 0 (zero) to the Client Characteristic Configuration descriptor for that characteristic through call to method WriteClientCharacteristicConfigurationDescriptorAsync with parameter GattClientCharacteristicConfigurationDescriptorValue.None :
GattCommunicationStatus status =
await myGattchar.WriteClientCharacteristicConfigurationDescriptorAsync(
GattClientCharacteristicConfigurationDescriptorValue.None);

Answer 2

Just dispose all objects related to the device. That will disconnect the device, unless there are other apps connected to it.

Answer 3

For my UWP app, even though I've used Dispose() methods, I still received notifications. What helped me was setting my device and characteristics to null. Example:
device.Dispose();
device = null;
Not all to certain of how "correct" this programming is, but it's been working fine for me so far.

Answer 4

The UWP Bluetooth BLE sample code from Microsoft (dispose the BLE device) didn't work for me. I had to add code (dispose the service) to disconnect the device.
private async Task<bool> ClearBluetoothLEDeviceAsync()
{
if (subscribedForNotifications)
{
// Need to clear the CCCD from the remote device so we stop receiving notifications
var result = await registeredCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(GattClientCharacteristicConfigurationDescriptorValue.None);
if (result != GattCommunicationStatus.Success)
{
return false;
}
else
{
selectedCharacteristic.ValueChanged -= Characteristic_ValueChanged;
subscribedForNotifications = false;
}
}
selectedService?.Dispose(); //added code
selectedService = null; //added code
bluetoothLeDevice?.Dispose();
bluetoothLeDevice = null;
return true;
}

Answer 5

Remember you must call -= for events you have called += or Dispose() will never really garbage collect correctly. It's a little more code, I know. But it's the way it is.
Not just with bluetooth stuff, I will remind you - with everything. You can't have hard referenced event handlers and get garbage collection to work as expected.

Answer 6

Doing all the disposing and null references suggested didn't achieve the Windows (Windows Settings) disconnection I was looking for.
But dealing with IOCTL through DeviceIoControl did the job.

Answer 7

I found that after calling GattDeviceService.GetCharacteristicsAsync(), BluetoothLeDevice.Dispose() does not work. So I dispose the Service I don't need.
GattCharacteristicsResult characteristicsResult = await service.GetCharacteristicsAsync();
if (characteristicsResult.Status == GattCommunicationStatus.Success)
{
foreach (GattCharacteristic characteristic in characteristicsResult.Characteristics)
{
if (characteristic.Uuid.Equals(writeGuid))
{
write = characteristic;
}
if (characteristic.Uuid.Equals(notifyGuid))
{
notify = characteristic;
}
}
if (write == null && notify == null)
{
service.Dispose();
Log($"Dispose service: {service.Uuid}");
}
else
{
break;
}
}
Finally, when I want to disconnect the Bluetooth connection
write.Service.Dispose();
device.Dispose();
device = null;