Detec U-Disk Insert and Remove

Zuobai

I now use the Windows platform to develop QML program, this program needs a function is to detect the insertion and removal of the U disk, need to output the insertion and removal of the drive letter,I found a program based on Qidget, but when I tried to port it to my QML program, Qt Creator prompted me"QWidget: Cannot create a QWidget without QApplication".
Does anyone have a solution? I would be very grateful if you could solve my problem

JonB

@Zuobai
Assuming this code, whatever it is, is what you want to detect the situation, remove anything in it other than the core detection of the insertion/removal of the disk and then use that. You do not need a QWidget or any UI for that, and anything QWidget is not compatible with a QML application.

JoeCFD

@Zuobai The detection part has nothing to do with QWidget. Simply take out that part and add it to your qml app.

JoeCFD

@JonB I guess it is possible to mix QWidget and QML together with QQuickWidget.

JonB

@JoeCFD
Since the OP is stuck on "QWidget: Cannot create a QWidget without QApplication". would it not make sense for them to look at the code and remove whatever is there for a widget, presumably just to display some result, given they are in a QML application? I should be surprised if wanting to detect "the insertion and removal of the drive letter" required any kind of QWidget, it just seems an unnecessary thing to try to support.

JoeCFD

@JonB You are right in this scenario. I guess the error shows up because QGuiApplication is applied. When QWidget is added, QApplication is needed. I do mix them in my app.

JonB

@JoeCFD I understand, I just did not want to complicate for this OP.

Zuobai

@JonB
Thank you for your reply,In order to better discuss this issue, I will attach the code that I have processed here, I removed all the interface code, only keeping the core part that identifies the USB flash drive insertion, and then there is the situation I mentioned earlier, "QWidget: Cannot create a QWidget without QApplication" because I am rewriting a function that inherits from "QWidget" and my question is how I can integrate this code into my QML interface project.

// Udisk.Cpp

char UDISKScanner::FirstDriveFromUDisk(ulong unitmask)
{
    char i;
    for( i = 0 ; i < 26 ; i++)
    {
        if( unitmask & 0x1)
        {
            break;
        }

        unitmask = unitmask >> 1;
    }

    return (i+'A');
}

bool UDISKScanner::nativeEventFilter(const QByteArray &eventType, void *message, long *result)
{
    MSG* msg = reinterpret_cast<MSG*>(message);
    int msgType = msg->message;
    if (msgType == WM_DEVICECHANGE)
    {
        PDEV_BROADCAST_HDR lpdb = (PDEV_BROADCAST_HDR)msg->lParam;
        switch (msg->wParam)
        {
        case DBT_DEVICEARRIVAL:
            if (lpdb->dbch_devicetype == DBT_DEVTYP_VOLUME)
            {
                PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;
                if (lpdbv->dbcv_flags == 0)
                {
                    QString strUSBDisk = QString(this->FirstDriveFromUDisk(lpdbv->dbcv_unitmask));
                    emit sigUDiskCome(strUSBDisk);
                }
            }
            break;
        case DBT_DEVICEREMOVECOMPLETE:
            if (lpdb->dbch_devicetype == DBT_DEVTYP_VOLUME)
            {
                PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;
                if (lpdbv->dbcv_flags == 0)
                {
                    QString strUSBDisk = QString(this->FirstDriveFromUDisk(lpdbv->dbcv_unitmask));
                    emit sigUDiskRemove(strUSBDisk);
                }
            }
            break;
        case DBT_DEVNODES_CHANGED:
            break;
        default:
            break;
        }
    }
    return QWidget::nativeEvent(eventType, message, result);
}

J.Hilk

nativeEvent is indeed a QWidget based virtual function and not part of QObject. so you're out of luck on the direct translation to QML

but, my guess is a NativeEventFilter on your QCoreApplication should do the trick.

Zuobai

@JoeCFD
Thank you for your reply, I agree with your idea, which coincides with my initial idea, I will extract the USB flash drive identification core part published in "#8", we can continue to discuss this problem

Zuobai

@J-Hilk
Thank you for your reply,
Indeed, after I discovered that the "nativeEvent" inherits from the "QWidget", I tried something else, as you said, using the "NativeEventFilter" that inherits from the "QCoreApplication ", but the problem remained. How can I modify and adjust it