IGameInputDevice::GetXInputDeviceIndex

bool GetXInputDeviceIndex(
    uint32_t* index
);

void CALLBACK OnDeviceEvent(
    GameInputCallbackToken callbackToken,
    void* context,
    GameInputDeviceEvent deviceEvent,
    IGameInputDevice* device) noexcept
{
    if (deviceEvent == GameInputDeviceEventXInputIndexUpdated)
    {
        uint32_t index = 0;
        if (device->GetXInputDeviceIndex(&index))
        {
            // The device is now assigned to XInput user index 'index'.
        }
        else
        {
            // The device no longer has an XInput user index.
        }
    }
}