在我的Qt应用程序中收到了WM_DEVICECHANGE但没有收到DBT_DEVICEARRIVAL

Question

我正在按照一个示例来检测Windows 7中的USB闪存驱动器插件和插件检测.我确实收到了通知,WM_DEVICECHANGE但没有收到DBT_DEVICEARRIVALUSB设备的插件.我的代码如下:

/*******************************************
*             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;
}