Detec U-Disk Insert and Remove

[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