Bug in Qt 5.12 drag n'drop ?

skylendar · 17 Dec 2018, 15:59

Found the puzzle in the examples. It works, but in my case the draggable widget is placed in a QTreeWidget, not just an ordinary QWidget.

mrjj · 17 Dec 2018, 16:44

Hi
well it its almost the same unless you used
QStandardItemModel::dropMimeData()
or something like that.

skylendar · 17 Dec 2018, 16:52

@mrjj

I can drag from my QTreeWidget, but I can't drop anymore my icon onto my QWidget target, whereas it worked in the previous version of qt (5.11).

Everything seems ok, but the dropEvent() method of my QWidget isn't activated (setAcceptDrop() is set to true, of course)

mrjj · 17 Dec 2018, 16:57

@skylendar
Check the
http://doc.qt.io/qt-5/qtwidgets-draganddrop-puzzle-example.html
as it drops from ListWidget to Widget.

skylendar · 17 Dec 2018, 17:02

@mrjj

But I already did that... The codes are very similar, but in my case it doesn't work anymore

Christian Ehrlicher · 17 Dec 2018, 18:49

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

The codes are very similar

So you should modify one of them until you hit or fix the problem...

mrjj · 17 Dec 2018, 18:48

@skylendar
Ok but it does not seems Qt related then as those sample didn't change between
5.11 and 5.12 so if they still work it seems unlikely something broke on Qt level.

skylendar · 18 Dec 2018, 07:34

@mrjj

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

skylendar · wrote on 17 Dec 2018, 18:49

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

jsulm · 21 Dec 2018, 13:21

@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 · J jsulm 18 Dec 2018, 07:34

@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 · 21 Dec 2018, 18:44

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 · wrote on 21 Dec 2018, 15:20

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 · wrote on 21 Dec 2018, 18:44

@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 · 21 Dec 2018, 19:16

@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 · wrote on 21 Dec 2018, 19:16

@Christian-Ehrlicher

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

Christian Ehrlicher · wrote on 21 Dec 2018, 19:26

@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 · wrote on 31 Dec 2018, 01:37

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

cawlfj · S SGaist 14 Dec 2018, 22:36

@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 · wrote on 31 Dec 2018, 09:05

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.