App crashing with custom drag and drop for QTabBar (Qt 6.5.2 for MacOS)

[cadol001]

Here is a minimal example. Drag and drop a tab anywhere and it will crash. Deleting the drag object after exec doesn't fix the issue.

Any help is much appreciated, thank you!

#include <QApplication>
#include <QDrag>
#include <QTabBar>
#include <QTabWidget>
#include <QMainWindow>
#include <qmimedata.h>

class my_tabbar : public QTabBar
{
public:
    my_tabbar(QWidget* parent) : QTabBar(parent)
    {

    }

protected:
    void mouseMoveEvent(QMouseEvent* event)
    {
        QDrag* drag = new QDrag(this);
        QMimeData mdata = QMimeData();
        mdata.setText("ex");
        drag->setMimeData(&mdata);
        drag->exec();
    }
};

class my_tabwidget : public QTabWidget
{
public:
    my_tabwidget(QWidget* parent) : QTabWidget(parent)
    {
        QTabBar* bar = new my_tabbar(parent);
        setTabBar(bar);
        setAcceptDrops(true);
        setMovable(true);
        for(int x = 0; x < 5; x++)
        {    addTab(new QWidget(), "tab"+QString::number(x)); }
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    my_tabwidget tabWidget(&w);
    w.setGeometry(QRect(0,0,600,600));
    tabWidget.setGeometry(QRect(0,0,600,600));
    w.show();
    return a.exec();
}

[jsulm]

@cadol001 said in App crashing with custom drag and drop for QTabBar (Qt 6.5.2 for MacOS):

QTabBar* bar = new my_tabbar(parent);

Why are you setting the bar on the parent and not this?
Run through debugger and check the stack trace to see why the app crashes.

[CPPUIX]

Hi,

I think you have the same problem as in this thread : app crashing on dropevent in qtabwidget.

If you read QDrag documentation you'll notice the QMimeData in that example is allocated on the heap.

If you read QDrag::setMimeData, you'll notice it takes a pointer, which you worked around by passing &mdata.

If you read QMimeData documentation you'll notice it says:

QMimeData objects are usually created using new...

Using a debugger would also help to see what happened.

[cadol001]

@Abderrahmene_Rayene thank you using new to make the mime data fixed it

[jsulm]

@cadol001 You should thank @Abderrahmene_Rayene :-)