QDrag / QDropEvent combase error : Class not registered

[rtavakko]

Hi everyone,

I'm using standard Qt drag / drop event code to transfer data between two test widgets. Everything works well, except that I get the combase error below and GUI thread stalls when I start either event (e.g. when I drag the mouse over the widget receiving the event). I'm running Qt 5.12.0 MSVC2017 64 bit on a 64 bit Windows 10 machine.

onecore\com\combase\dcomrem\resolver.cxx(2491)\combase.dll!00007FFD1A377992: (caller: 00007FFD1A2C2075) ReturnHr(1) tid(399c) 80040154 Class not registered

Drag event and mime data creation:

QDrag *drag = new QDrag(this);

QString text = QString("TEXT");

QMimeData *mimeData = new QMimeData();
mimeData->setText(text);

drag->setMimeData(mimeData);

Qt::DropAction dropAction = drag->exec(Qt::CopyAction|Qt::MoveAction);

Drop events in the test widget:

void TestWidget::dragMoveEvent(QDragMoveEvent *event)
{
    if(event->mimeData()->hasUrls() || event->mimeData()->hasText())
        event->acceptProposedAction();
}

void TestWidget::dragEnterEvent(QDragEnterEvent *event)
{
    if(event->mimeData()->hasUrls() || event->mimeData()->hasText())
        event->acceptProposedAction();
}

void TestWidget::dropEvent(QDropEvent *event)
{
    qDebug()<<event->mimeData()->text();
}

Have you seen this issue before? How do I start troubleshooting this?

Cheers!

[SGaist]

Hi,

Might be unrelated to Qt.

See this bug report for example.

[rtavakko]

@SGaist

Thanks! I looked at a few different threads and thought maybe this is related to Windows 32-bit vs 64-bit DLLs.

I compiled a 32-bit version and the problem remained. I tried Release builds for both 32-bit and 64-bit and the problem went away. Maybe the MSVC debugger is not finding some DLLs or has incorrect settings?

If you have any tips on troubleshooting further I would definitely appreciate it!

Cheers!

[SGaist]

Do you have the same issue if you start one of the Qt drag and drop examples ?

[rtavakko]

@SGaist Yes, I see the same issue with the examples in MSVC debug builds, but release works without errors

[SGaist]

Would it be possible to test a more recent version of Visual Studio ?

[rtavakko]

@SGaist Later than MSVC 2017 or a Qt Creator version later than 4.5.0?

[SGaist]

MSVC or rather the compiler. Qt Creator shall have nothing to do with that issue.

You could also check with the MinGW build to see if you have a similar issue. It might be less intrusive than adding another VS installation to your machine.

[rtavakko]

@SGaist Good point, I'll try the MINGW build first and post the results. Thanks for your help!