[Qt6] StartDrag making crash on Qt6

[ChristianEhrlicher]

Can you please provide a minimal, compilable example so we can reproduce the issue?

/edit: and are you really sure it worked with 5.15?

[Alundra]

This code reproduces the issue, you can start to drag and drop "Item1" and you will see a crash immediately once you move the mouse during drag and drop.

#include <QApplication>
#include <QDrag>
#include <QListWidget>
#include <QMainWindow>
 
class CustomListWidget : public QListWidget
{
public:
    CustomListWidget(QWidget* parent) : QListWidget(parent)
    {}
 
protected:
    void startDrag(Qt::DropActions supportedActions) override
    {
        QDrag* drag = new QDrag(this);
        drag->setMimeData(mimeData(selectedItems()));
        drag->exec(supportedActions);
    }
};
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    CustomListWidget customListWidget(&w);
    customListWidget.setMovement(QListView::Snap);
    customListWidget.setViewMode(QListView::IconMode);
    customListWidget.setResizeMode(QListView::Adjust);
    customListWidget.setSelectionMode(QAbstractItemView::ExtendedSelection);
    customListWidget.setDragDropMode(QAbstractItemView::DragDrop);
    customListWidget.setDefaultDropAction(Qt::MoveAction);
    customListWidget.setIconSize(QSize(64, 64));
    customListWidget.setUniformItemSizes(true);
    customListWidget.setSortingEnabled(true);
    customListWidget.setWrapping(true);
    customListWidget.addItem("Item1");
    customListWidget.addItem("Item2");
    w.show();
    return a.exec();
}

#include <QApplication>
#include <QDrag>
#include <QListWidget>
#include <QMainWindow>

class CustomListWidget : public QListWidget
{
public:
    CustomListWidget(QWidget* parent) : QListWidget(parent)
    {}

protected:
    void startDrag(Qt::DropActions supportedActions) override
    {
        QDrag* drag = new QDrag(this);
        drag->setMimeData(mimeData(selectedItems()));
        drag->exec(supportedActions);
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    CustomListWidget customListWidget(&w);
    customListWidget.setMovement(QListView::Snap);
    customListWidget.setViewMode(QListView::IconMode);
    customListWidget.setResizeMode(QListView::Adjust);
    customListWidget.setSelectionMode(QAbstractItemView::ExtendedSelection);
    customListWidget.setDragDropMode(QAbstractItemView::DragDrop);
    customListWidget.setDefaultDropAction(Qt::MoveAction);
    customListWidget.setIconSize(QSize(64, 64));
    customListWidget.setUniformItemSizes(true);
    customListWidget.setSortingEnabled(true);
    customListWidget.setWrapping(true);
    customListWidget.addItem("Item1");
    customListWidget.addItem("Item2");
    w.show();
    return a.exec();
}

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[ChristianEhrlicher]

Thx for the reproducer and as I expected it's just by accident that it does not crash with Qt5. QIconModeViewBase::itemsRect() is called with an empty container due to your custom startDrag() function. The original startDrag() fills this container before calling drag->exec(). Will create a bug report for it.

/edit: Here the ink to the bugreport: https://bugreports.qt.io/browse/QTBUG-89434

[Alundra]

Thanks! I added myself as watcher