Qt and Device Notifications

webzoid

Can anyone share any pearls of wisdom, please, relating to registering for device notifications in Qt 5.11.1.

Having taken some working MFC code and ported it across to Qt, I can't for the life of me get my device to trigger any notifications.

My code is thus:

static GUID	GUID_DFU = { 0x3fe809ab, 0xfb91, 0x4cb5, { 0xa6, 0x43, 0x69, 0x67, 0x0d, 0x52, 0x36, 0x6e } };

void MainWindow::registerForDeviceNotifications()
{
	HWND hWnd = (HWND)this->winId();

	DEV_BROADCAST_DEVICEINTERFACE filter;
	memset(&filter, 0, sizeof(DEV_BROADCAST_DEVICEINTERFACE));
	filter.dbcc_size = sizeof(filter);
	filter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
	// Register specifically for the DFU GUID device notifications
	filter.dbcc_classguid = GUID_DFU;

	// Register for the DFU device notifications
	RegisterDeviceNotification(hWnd, &filter, DEVICE_NOTIFY_WINDOW_HANDLE);
}

bool MainWindow::nativeEvent(const QByteArray &eventType, void *message, long *result)
{
	_DEV_BROADCAST_HEADER* hdr = nullptr;

	// Get the MSG stuct
	MSG* msg = static_cast<MSG *>(message);
	UINT type = msg->message;

	WPARAM wParam = msg->wParam;
	qDebug() << "type:" << type;
	qDebug() << "wParam:" << wParam;

        // THIS NEVER HAPPENS
        // THE ONLY THING THAT SEEMS TO BE CORRECT IS THAT wParam == WM_DEVICECHANGE
	if (type == DBT_DEVICEARRIVAL) {
		qDebug() << "APP: Device Arrival";

		hdr = (_DEV_BROADCAST_HEADER *)msg->lParam;

		if (hdr->dbcd_devicetype == DBT_DEVTYP_DEVICEINTERFACE) {
			refreshDevices();
		}
	}
	else if (type == DBT_DEVICEREMOVECOMPLETE) {
		qDebug() << "APP: Device Remove Complete";
	}

	return false;
}

The only thing I can seem to get to work is when I check wParam == WM_DEVICECHANGE but every other example I have seen using the nativeEvent do not confirm this.

Any help would be greatly appreciated.

webzoid

Ok, I managed to resolve this...

Turns out implementing a custom QAbstractNativeEventFilter and installing via the QApplication::installNativeEventFilter function does the trick!

I haven't seen many examples of this around so I'll post back my complete working code incase it is useful to someone else.

SGaist

Hi,

Glad you found out and thanks for sharing !

Rather than just posting your example here, would you consider adding it to the Qt documentation ? That would allow more people to easily find it.

webzoid

@SGaist Yes, I would certainly consider that. How would one go about accomplishing such a task?

SGaist

You can start by taking a look at the gerrit introduction and the related article linked at the top.

I know it can look a bit scary but don't worry, it's a pretty thorough document to get you nicely started. Then you can clone the qtbase module and modify the QAbstractNativeEventFilter documentation. From a quick look, there are already code snippet for Linux and macOS that you can take inspiration from.