Warning when closing an undocked qwidget

[Mwoua_Leddar]

Hello,
I've recently migrated code from qt 5.7 to qt 5.15 and when I close an undocked dock widget, I get this warning :

QMainWindowLayout::tabPosition called with out-of-bounds value '0'

If I close it programmaticaly by calling DockWidget->close(), there si no warning.
If I dock and undock it before closing it, there is no warning either.

What does this error mean?

I have stepped in qt source, and when I close the widget by clicking on the X, the dockwidget close event call d->endDrag(true);
But it does not call that function when I close it programmatically or when the widget is docked.

[SGaist]

Hi,

Can you provide a minimal compilable example that shows that behaviour ?

[Mwoua_Leddar]

The code is complex, and a single example doesnt show the issue. Thats why I hoped someone could explain what the error message means, so I would know where to search the issue.

Gonna keep debugging on my side and update here if I fond something usefull

[Christian Ehrlicher]

Install Qt debug libs, set a breakpoint on the warning message and show us the backtrace.

[Mwoua_Leddar]

Call stack is

Qt5Widgetsd.dll!QMainWindowLayout::tabPosition(Qt::DockWidgetArea area) Line 1588 C++
Qt5Widgetsd.dll!QDockWidgetPrivate::endDrag(bool abort) Line 870 C++
Qt5Widgetsd.dll!QDockWidget::closeEvent(QCloseEvent * event) Line 1469 C++

And in each fonction (check //This line comment)

QTabWidget::TabPosition QMainWindowLayout::tabPosition(Qt::DockWidgetArea area) const
{
    const auto dockPos = toDockPos(area);
    if (dockPos < QInternal::DockCount)
        return tabPositions[dockPos];
    qWarning("QMainWindowLayout::tabPosition called with out-of-bounds value '%d'", int(area)); //This line
    return QTabWidget::North;
}

void QDockWidgetPrivate::endDrag(bool abort)
{
    Q_Q(QDockWidget);
    Q_ASSERT(state != nullptr);

    q->releaseMouse();

    if (state->dragging) {
        const QMainWindow *mainWindow = mainwindow_from_dock(q);
        Q_ASSERT(mainWindow != nullptr);
        QMainWindowLayout *mwLayout = qt_mainwindow_layout(mainWindow);

        if (abort || !mwLayout->plug(state->widgetItem)) {
            if (hasFeature(this, QDockWidget::DockWidgetFloatable)) {
                // This QDockWidget will now stay in the floating state.
                if (state->ownWidgetItem) {
                    delete state->widgetItem;
                    state->widgetItem = nullptr;
                }
                mwLayout->restore();
                QDockWidgetLayout *dwLayout = qobject_cast<QDockWidgetLayout*>(layout);
                if (!dwLayout->nativeWindowDeco()) {
                    // get rid of the X11BypassWindowManager window flag and activate the resizer
                    Qt::WindowFlags flags = q->windowFlags();
                    flags &= ~Qt::X11BypassWindowManagerHint;
                    q->setWindowFlags(flags);
                    setResizerActive(q->isFloating());
                    q->show();
                } else {
                    setResizerActive(false);
                }
                if (q->isFloating()) { // Might not be floating when dragging a QDockWidgetGroupWindow
                    undockedGeometry = q->geometry();
#if QT_CONFIG(tabwidget)
                    tabPosition = mwLayout->tabPosition(mainWindow->dockWidgetArea(q)); //This line
#endif
                }
                q->activateWindow();
            } else {
                // The tab was not plugged back in the QMainWindow but the QDockWidget cannot
                // stay floating, revert to the previous state.
                mwLayout->revert(state->widgetItem);
            }
        }
    }
    delete state;
    state = nullptr;
}

void QDockWidget::closeEvent(QCloseEvent *event)
{
    Q_D(QDockWidget);
    if (d->state)
        d->endDrag(true); //This line
    QWidget::closeEvent(event);
}

And if I close the widget programatically, we dont go in d->enDrag(true) from closeEvent

[Christian Ehrlicher]

So you somehow get into QDockWidgetPrivate::initDrag(). Is it possible to set a breakpoint there to see why it is entered?

[Mwoua_Leddar]

When closing the widget with the mouse (top right button)

Call stack is

Qt5Widgetsd.dll!QDockWidgetPrivate::initDrag(const QPoint & pos, bool nca) Line 778 C++
Qt5Widgetsd.dll!QDockWidgetPrivate::nonClientAreaMouseEvent(QMouseEvent * event) Line 1043 C++
Qt5Widgetsd.dll!QDockWidget::event(QEvent * event) Line 1586 C++
Qt5Widgetsd.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e) Line 3630 C++
Qt5Widgetsd.dll!QApplication::notify(QObject * receiver, QEvent * e) Line 3580 C++
Qt5Cored.dll!QCoreApplication::notifyInternal2(QObject * receiver, QEvent * event) Line 1063 C++
Qt5Cored.dll!QCoreApplication::forwardEvent(QObject * receiver, QEvent * event, QEvent * originatingEvent) Line 1079 C++
Qt5Widgetsd.dll!QWidgetWindow::handleNonClientAreaMouseEvent(QMouseEvent * e) Line 505 C++
Qt5Widgetsd.dll!QWidgetWindow::event(QEvent * event) Line 308 C++
Qt5Widgetsd.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e) Line 3630 C++
Qt5Widgetsd.dll!QApplication::notify(QObject * receiver, QEvent * e) Line 2970 C++
Qt5Cored.dll!QCoreApplication::notifyInternal2(QObject * receiver, QEvent * event) Line 1063 C++
Qt5Cored.dll!QCoreApplication::sendSpontaneousEvent(QObject * receiver, QEvent * event) Line 1471 C++
Qt5Guid.dll!QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent * e) Line 2278 C++
Qt5Guid.dll!QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent * e) Line 2003 C++
Qt5Guid.dll!QWindowSystemInterface::sendWindowSystemEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 1181 C++

And for the last function:

void QDockWidgetPrivate::nonClientAreaMouseEvent(QMouseEvent *event)
{
    Q_Q(QDockWidget);

    int fw = q->style()->pixelMetric(QStyle::PM_DockWidgetFrameWidth, nullptr, q);

    QWidget *tl = q->topLevelWidget();
    QRect geo = tl->geometry();
    QRect titleRect = tl->frameGeometry();
    {
        titleRect.setLeft(geo.left());
        titleRect.setRight(geo.right());
        titleRect.setBottom(geo.top() - 1);
        titleRect.adjust(0, fw, 0, 0);
    }

    switch (event->type()) {
        case QEvent::NonClientAreaMouseButtonPress:
            if (!titleRect.contains(event->globalPos()))
                break;
            if (state != nullptr)
                break;
            if (qobject_cast<QMainWindow*>(parent) == 0 && qobject_cast<QDockWidgetGroupWindow*>(parent) == 0)
                break;
            if (isAnimating())
                break;
            initDrag(event->pos(), true); //This line
            if (state == nullptr)
                break;
            state->ctrlDrag = (event->modifiers() & Qt::ControlModifier) ||
                              (!hasFeature(this, QDockWidget::DockWidgetMovable) && q->isFloating());
            startDrag();
            break;
        case QEvent::NonClientAreaMouseMove:
            if (state == nullptr || !state->dragging)
                break;

#ifndef Q_OS_MAC
            if (state->nca) {
                endDrag();
            }
#endif
            break;
        case QEvent::NonClientAreaMouseButtonRelease:
#ifdef Q_OS_MAC
                        if (state)
                                endDrag();
#endif
                        break;
        case QEvent::NonClientAreaMouseButtonDblClick:
            _q_toggleTopLevel();
            break;
        default:
            break;
    }
}

[Christian Ehrlicher]

This is strange, I don't see anything within QDockWidget sources. But there were mouse handling changes in 5.12 - can you maybe check with 5.11.x and 5.12.x to see if this may be the culprit?

[Mwoua_Leddar]

Just run basic tests with version 5.11.3 and 5.12.0.
Looks like I dont have the issue with any of them

[Christian Ehrlicher]

Can you check latest 5.12.x?

[Mwoua_Leddar]

I have managed to reproduce it with a really basic example:

#include <QApplication>
#include <QMainWindow>
#include <QLabel>
#include <QDockWidget>


int main(int argc, char* argv[])
{
    QApplication lApp(argc, argv);

    QMainWindow a;
    a.setCentralWidget(new QLabel("Main"));
    a.show();

    auto lWindow = new QDockWidget(&a);
    lWindow->setFloating(true);
    lWindow->show();

    return lApp.exec();
}

and the cmake file im using:

cmake_minimum_required(VERSION 3.16.0)
set(CMAKE_VERBOSE_MAKEFILE ON CACHE BOOL "ON" FORCE)

project(test)

#Qt libs and macro
SET(CMAKE_PREFIX_PATH "C:/Qt/5.15.1/msvc2019_64")

set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)

find_package(Qt5 COMPONENTS Widgets Gui REQUIRED)

set(Src
    ${CMAKE_CURRENT_LIST_DIR}/main.cpp
)

add_executable(Test ${Src})
target_link_libraries(Test PRIVATE Qt5::Widgets Qt5::Gui)

[Mwoua_Leddar]

Ran more test with this simple example, the issue is actually there with qt 5.11.3 ,5.12.0 and 5.12.9.

Edit:
I confirm the issue is not here with 5.7.1

Should I test with more versions?
Raise a bug?

Do you know if there is a workaround?

[Christian Ehrlicher]

So you can also reproduce it with 5.11? Then it's not the change I thought.
It would be nice when you find some time to investigate with which version the issue came in.

[jsulm]

This post is deleted!

[Mwoua_Leddar]

The issue is there in 5.9.

Cant test between 5.7.1 and 5.9, versions are not available for download

[Christian Ehrlicher]

Thx for the information. I would suggest you to create a bug reports with all your findings. Sadly I can't compile such an old version on my system anymore so I can't hep figuring out which exact commit creates this issue.

[Mwoua_Leddar]

Bug report created: https://bugreports.qt.io/browse/QTBUG-88157
(Cant figure out how to properly format the code in the report)

[Christian Ehrlicher]

Thx, I reformatted the code, the CMakeLists.txt is not needed.