QtBluetooth Win10, how to check if bluetooth adapter is available and ON?

Question

I'm using QtBluetooth under Win10. Works fine.

However, as my app is deployed both on laptops (that may or may not have a BT adapter) and desktops (that are likely not to have an adapter), I'd like to programmatically check if the adapter is available or not (present and enabled).

Considering the documentation, I tested 4 functions:

bool isBluetoothAvailable1()
{
    return !QBluetoothLocalDevice::allDevices().empty();
}

bool isBluetoothAvailable2()
{
    QBluetoothLocalDevice localDevice;
    return localDevice.isValid();
}

bool isBluetoothAvailable3()
{
    std::shared_ptr<QLowEnergyController> created( QLowEnergyController::createPeripheral() );
    if ( created )
    {
        if ( !created->localAddress().isNull() )
            return true;
    }
    return false;
}

bool isBluetoothAvailable4()
{
    std::shared_ptr<QLowEnergyController> created( QLowEnergyController::createCentral( QBluetoothDeviceInfo() ) );
    if ( created )
    {
        if ( !created->localAddress().isNull() )
            return true;
    }
    return false;
}

But when I run my code on a Win10 laptop, they all return false! Even if I can search an connect a remote device using the QBluetooth API.

What's the right method to know if a BLE adapter is available?

Answer 1

The correct solution would be to use isBluetoothAvailable1() because the call to allDevices() lists all connected Bluetooth adapters. However, this does not works on Windows.

I do not fully understand their reasoning, but there are 2 Windows implementations of this function in Qt.

https://code.qt.io/cgit/qt/qtconnectivity.git/tree/src/bluetooth/qbluetoothlocaldevice_win.cpp?h=5.15.2

https://code.qt.io/cgit/qt/qtconnectivity.git/tree/src/bluetooth/qbluetoothlocaldevice_winrt.cpp?h=5.15.2

And by default it uses the one that always returns empty list (qbluetoothlocaldevice_win.cpp).

QList<QBluetoothHostInfo> QBluetoothLocalDevice::allDevices()
{
    QList<QBluetoothHostInfo> localDevices;
    return localDevices;
}

The simplest solution is to use the code from the other Windows implementation that works (qbluetoothlocaldevice_winrt.cpp)

#include <Windows.h>
#include <BluetoothAPIs.h>

QList<QBluetoothHostInfo> allDevices()
{
    BLUETOOTH_FIND_RADIO_PARAMS params;
    ::ZeroMemory(&params, sizeof(params));
    params.dwSize = sizeof(params);

    QList<QBluetoothHostInfo> foundAdapters;

    HANDLE hRadio = nullptr;
    if (const HBLUETOOTH_RADIO_FIND hSearch = ::BluetoothFindFirstRadio(&params, &hRadio)) {
        for (;;) {
            BLUETOOTH_RADIO_INFO radio;
            ::ZeroMemory(&radio, sizeof(radio));
            radio.dwSize = sizeof(radio);

            const DWORD retval = ::BluetoothGetRadioInfo(hRadio, &radio);
            ::CloseHandle(hRadio);

            if (retval != ERROR_SUCCESS)
                break;

            QBluetoothHostInfo adapterInfo;
            adapterInfo.setAddress(QBluetoothAddress(radio.address.ullLong));
            adapterInfo.setName(QString::fromWCharArray(radio.szName));

            foundAdapters << adapterInfo;

            if (!::BluetoothFindNextRadio(hSearch, &hRadio))
                break;
        }

        ::BluetoothFindRadioClose(hSearch);
    }

    return foundAdapters;
}

Also you will need to link the necessary libraries Bthprops and ws2_32.