Bug in Qt 5.12 drag n'drop ?

[skylendar]

@mrjj

On the contrary ! My code didn't change between 5.11 and 5.12, and suddenly it doesn't work...

[skylendar]

@Christian-Ehrlicher
it's exactly what I'm doing :-£

[jsulm]

@skylendar said in Bug in Qt 5.12 drag n'drop ?:

My code didn't change between 5.11 and 5.12, and suddenly it doesn't work

This does not prove that there is a bug in Qt (though there could be).
It could be a problem in your code which didn't cause issues with Qt 5.11 but does with Qt 5.12.
So, before saying there is a bug in Qt you should really prove that.

[armindev]

@jsulm said in Bug in Qt 5.12 drag n'drop ?:

t prove that there is a bug in

I also have an Application which has a drag n'drop problem since I've updated to Qt 5.12.0 (macOS 10.14.2 Mojave). The eventFilter method is not called anymore with QEvent::Drop

Therefore I can not drop anything into my QLineEdit derived object...

// MyLineEdit is derived from QLineEdit

bool MyLineEdit::eventFilter(QObject* object, QEvent* event)
{

    if(m_droppable) {

        if(event->type() == QEvent::DragEnter) {
            event->accept();
        }

        // since Qt 5.12.0 the following condition is never true! 
        if(event->type() == QEvent::Drop) {
             // this line is never reached
             // ..
        }

    }
}

[Christian Ehrlicher]

This works fine with 5.11 and 5.12 on Linux:

class MyLineEdit : public QLineEdit
{
    Q_OBJECT
public:
    using QLineEdit::QLineEdit;

    bool eventFilter(QObject *object, QEvent *event)
    {
        if (event->type() == QEvent::DragEnter)
            event->accept();
        if (event->type() == QEvent::Drop)
            qDebug() << "Drop";
        return QLineEdit::eventFilter(object, event);
    }
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyLineEdit le;
    le.installEventFilter(&le);
    le.show();
    return app.exec();
}

#include "main.moc"

If it does not work on Mac please open a bug report.

/edit: There were some dnd changes between 5.11 and 5.12: 10b3286313c78fa380b5fe676a7c14f3ae84f017 - it works fine on Linux, did not yet test on windows and don't have a mac...

[Maaz Momin]

Hello guys... Since we are talking about Drag and Drop. Can somebody also look into this bug report?

https://bugreports.qt.io/browse/QTBUG-70725

[armindev]

@Christian-Ehrlicher said in Bug in Qt 5.12 drag n'drop ?:

MyLineEdit

Hm... this works on mac too!

Seems to be a special constelation which doesn't work or it's a bug in specific circumstancens only...

[Christian Ehrlicher]

@armindev said in Bug in Qt 5.12 drag n'drop ?:

Seems to be a special constelation

Is it possible to simplify your program until the bug is gone away?

[armindev]

@Christian-Ehrlicher

I will try this but this will take a while ..

[Christian Ehrlicher]

@armindev said in Bug in Qt 5.12 drag n'drop ?:

I will try this but this will take a while ..

Thx and take your time. There seems to be something wrong in a corner case and it would be really good to find it out :)

[cawlfj]

@skylendar
I found same bug in my app. change to 5.11.2 drop is ok

[cawlfj]

@SGaist
i found same bug also in my app. change back 5.11 drop come back.
windows10 qt5.12.0 QLinedit , can drag from QLineEdit , but can't drop to QLineEdit.
Sometimes press the "ctrl" can drop to QLineEdit.

[ModelTech]

I have checked the drag & drop in my app when running on Ubuntu 16.04. The drag is from a QListWidgetItem to a drop on a QGraphicsView. I appropriately overrode QGraphicsView::dropEvent (and all the drag methods of QGraphicsView). It still works in Qt5.12.0 although the willingness to accept the QMimeData constructed from the QListWidgetItem as a droppable on the QGraphicsView (visible as a change in the mouse pointer icon) seems to be less than it was with Qt5.7 that I used up to yesterday. No clue whether this is in any way related, but perhaps it brings some ideas of what causes the issue for dropping on a QLineEdit.

[SGaist]

@ModelTech can you provide a minimal compilable example that shows that change of behaviour ?

[ReDEnergy]

Hi. I had the same problem. Everything worked fine on Qt 5.7 then after I updated to Qt 5.12 dropping would not work at all.
At least in my case it seems that for previous version of Qt only implementing dragEnterEvent was enough but with 5.12 I had to also override the dragMoveEvent event.
So, basically I have this 2 things and now it works as expected. Hope it helps someone.

void QtDropArea::dragEnterEvent(QDragEnterEvent *event)
{
	event->acceptProposedAction();
}

// this was added after updating to Qt 5.12
void QtDropArea::dragMoveEvent(QDragMoveEvent *event)
{
	event->acceptProposedAction();
}

[Christian Ehrlicher]

@ReDEnergy said in Bug in Qt 5.12 drag n'drop ?:

QtDropArea

From what did you derive QtDropArea?

[ReDEnergy]

from the classic QWidget

[Christian Ehrlicher]

Thx for your hint with the dragMoveEvent() reimpl. I think I can reproduce your issue and also found the corresponding commit.

[Christian Ehrlicher]

Can you please check if you get a dragEnterEvent in the problematic case? I would guess no.
The problem was introduced with f8944a7f07112c85dc4f66848cabb490514cd28e which is a bugfix for QTBUG-67155.

[ReDEnergy]

Great to hear that. So, I suppose what I did is a workaround for the moment, but at least it works.