WM_DEVICECHANGE received but not DBT_DEVICEARRIVAL in my Qt app - c++

Question

I am following an example to detect USB flash drive plugin and plugout detection in Windows 7. I do receive the notification WM_DEVICECHANGE but not DBT_DEVICEARRIVAL which is when USB device is plugged in. My code is below:
/*******************************************
* WINDOWS EVENTS
********************************************/
/*We use the first WM_PAINT event to get the handle of main window
and pass it to RegisterDeviceNotification function.
It not possible to do this in the contructor because the
main window does not exist yet.
WM_DEVICECHANGE event notify us that a device is attached or detached */
bool USBexample::nativeEvent(const QByteArray & eventType, void * message, long * result)
{
MSG * msg = static_cast< MSG * > (message);
int msgType = msg->message;
if(msgType == WM_PAINT)
{
if(!msgp) //Only the first WM_PAINT
{
GUID InterfaceClassGuid = HID_CLASSGUID;
DEV_BROADCAST_DEVICEINTERFACE NotificationFilter;
ZeroMemory( &NotificationFilter, sizeof(NotificationFilter) );
NotificationFilter.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
NotificationFilter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
NotificationFilter.dbcc_classguid = InterfaceClassGuid;
HWND hw = (HWND) this->effectiveWinId(); //Main window handle
hDevNotify = RegisterDeviceNotification(hw,&NotificationFilter, DEVICE_NOTIFY_WINDOW_HANDLE);
msgp = true;
}
}
if(msgType == WM_DEVICECHANGE)
{
qDebug() << "WM_DEVICECHANGE recieved";
PDEV_BROADCAST_HDR lpdb = (PDEV_BROADCAST_HDR)msg->lParam;
switch(msg->wParam)
{
case DBT_DEVICEARRIVAL: // never comes here!
if (lpdb -> dbch_devicetype == DBT_DEVTYP_DEVICEINTERFACE)
{
qDebug() << "DBT_DEVICEARRIVAL case";
PDEV_BROADCAST_DEVICEINTERFACE lpdbv = (PDEV_BROADCAST_DEVICEINTERFACE)lpdb;
int i = 0;
QString s;
//to find a better way for this...
while(lpdbv->dbcc_name[i] != 0)
{
s.append(lpdbv->dbcc_name[i]);
i++;
}
s = s.toUpper();
if(s.contains(MY_DEVICE_VIDPID))
emit USB_Arrived();
}
break;
case DBT_DEVICEREMOVECOMPLETE:
if (lpdb -> dbch_devicetype == DBT_DEVTYP_DEVICEINTERFACE)
{
qDebug() << "DBT_DEVICEREMOVECOMPLETE case";
PDEV_BROADCAST_DEVICEINTERFACE lpdbv = (PDEV_BROADCAST_DEVICEINTERFACE)lpdb;
int i = 0;
QString s;
//to find a better way for this...
while(lpdbv->dbcc_name[i] != 0)
{
s.append(lpdbv->dbcc_name[i]);
i++;
}
s = s.toUpper();
if(s.contains(MY_DEVICE_VIDPID))
emit USB_Removed();
}
break;
case DBT_DEVICEREMOVEPENDING :
{
qDebug() << "DBT_DEVICEREMOVEPENDING case";
}
break;
default:
{
qDebug() << "Went to Default case";
}
}
}
return false;
}

Answer 1

I figure this out and here is the solution if anyone else runs into similar issue.
The problem was InterfaceClassGuid in the line below.
GUID InterfaceClassGuid = HID_CLASSGUID;
HID_CLASSGUID was set to the following in my code:
#define HID_CLASSGUID {0x4d1e55b2, 0xf16f, 0x11cf,{ 0x88, 0xcb, 0x00, 0x11, 0x11, 0x00, 0x00, 0x30}}
This was wrong, I picked this up from example and never realized I would need to change it. There are different values to register for different kind of notifications and the help system was not that helpful in this case but here is the list of valid GUID values.
I changed it to the following and now I get the desired notifications.
#define HID_CLASSGUID {0x745a17a0,0x74d3, 0x11d0, 0xb6fe, 0x00a0c90f57da}

Answer 2

Another possible cause of this problem could be the incorrect handle of the window being passed to the RegisterDeviceNotification(...) call.
Wrong code:
QMainWindow w;
...
HANDLE windowId = w.window()->winId();
RegisterDeviceNotification(&windowId,&NotificationFilter,DEVICE_NOTIFY_WINDOW_HANDLE);
I was passing the wrong value for winId's address and I kept getting 7 for wparam although the device insertion and removal was getting detected.
After I changed it to use the correct address of the window handle, I passed this to the RegisterDeviceNotification call and it worked.
Correct code:
QMainWindow w;
...
HANDLE *windowId = (HANDLE *)w.window()->winId();
RegisterDeviceNotification(windowId,&NotificationFilter,DEVICE_NOTIFY_WINDOW_HANDLE);