tabifyDockWidget() adding unknown widgets

[Julieng]

I've just tried with empty customWidget and I continue to "leak" widgets.

[SGaist]

I just realized, when you call tabify, there's a QTabWidget that is created and tabs added for each widget you put together.

There you have the three widgets.

[Julieng]

Thanks SGaist, that's an interesting point ! So, how could I remove these QTabWidgets ? Do I have to do it before or after the following piece of code ?

 for(uncloseableDockWidget * w:m_widgets) {
      m_container->removeDockWidget(w);
      delete w;
}
m_widgets.clear();

[Julieng]

I tried to remove the central widget like this :

delete m_container->centralWidget();

and build a new one. I thought that these additional widgets would be "parented" to the central widget. However, it does not work. Any idea to delete it ?

[SGaist]

Well, I think you have found an edge case. From the quick look I did to the sources of QMainWindow and its internal classes, the fact that you are deleting the dock widget every time seems to not be handled in the "tabification" part (I have to take a deeper dive to ensure that).

I must say that it's pretty unusual to completely destroy dock widgets and recreate them like you are currently doing.

Would you mind providing a minimal compilable example to reproduce that ?

[Julieng]

Thanks SGaist, here is a complete exemple :

main.cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <iostream>
#include <QMainWindow>
#include <QDockWidget>
#include <QCloseEvent>
#include <QLabel>
#include <QPushButton>
#include <QBoxLayout>
#include <QApplication>

class uncloseableDockWidget : public QDockWidget {
    Q_OBJECT

public:
    /**
     * @brief Constructor
     * @param title: title
     * @param parent: parent widget
     * @param flags: flags
     */
    explicit uncloseableDockWidget(const QString & title, QWidget * parent = nullptr, Qt::WindowFlags flags = Qt::WindowFlags()) : QDockWidget(title, parent, flags) {
        setFeatures(QDockWidget::DockWidgetMovable | QDockWidget::DockWidgetFloatable);
        setAllowedAreas(Qt::AllDockWidgetAreas);
    }

    /**
     * @brief Destructor
     */
    virtual ~uncloseableDockWidget() override {}

public slots:
    /**
     * @brief Update view
     */
    virtual void updateView() = 0;

protected:
    /**
     * @brief Close event
     * @param event: event
     */
    void closeEvent(QCloseEvent * event) override {
        event->ignore();
    }
};

class dock : public uncloseableDockWidget {
    Q_OBJECT

public:
    dock(const QString & title, QWidget * parent = nullptr, Qt::WindowFlags flags = Qt::WindowFlags()) : uncloseableDockWidget(title, parent, flags) {}

    void updateView() override {}
};

class tab1 : public QWidget {
    Q_OBJECT

public:
    tab1(QWidget * parent = nullptr) : QWidget(parent) {
        QVBoxLayout * layout = new QVBoxLayout();
        setLayout(layout);
        QPushButton * bt = new QPushButton("test");
        layout->addWidget(bt);
        connect(bt, SIGNAL(clicked()), this, SIGNAL(btClicked()));
    }

signals:
    void btClicked();
};

class tab2 : public QWidget {
    Q_OBJECT

public:
    tab2(QWidget * parent = nullptr) : QWidget(parent) {
        QVBoxLayout * layout = new QVBoxLayout();
        setLayout(layout);
        m_content = new QMainWindow();
        layout->addWidget(m_content);
        m_content->setCentralWidget(new QLabel("test"));
    }

public slots:
    void update() {
        std::cout << "test1: " << QApplication::allWidgets().size() << std::endl;
        // Remove already existing dock widgets
        for(uncloseableDockWidget * w:m_docks) {
            m_content->removeDockWidget(w);
            delete w;
        }
        m_docks.clear();
        std::cout << "test2: " << QApplication::allWidgets().size() << std::endl;
        // Add new dock widgets
        m_docks.emplace_back(new dock("title1"));
        m_docks.emplace_back(new dock("title2"));
        m_docks.emplace_back(new dock("title3"));
        std::cout << "test3: " << QApplication::allWidgets().size() << std::endl;
        // Add and tabify dock widgets
        for(uncloseableDockWidget * w:m_docks)
            m_content->addDockWidget(Qt::RightDockWidgetArea, w);
        std::cout << "test4: " << QApplication::allWidgets().size() << std::endl;
        for(unsigned int i=1; i<m_docks.size(); i++)
            m_content->tabifyDockWidget(m_docks[i-1], m_docks[i]);
        std::cout << "test5: " << QApplication::allWidgets().size() << std::endl;
        if(m_docks.size())
            m_docks.front()->raise();
        std::cout << "test6: " << QApplication::allWidgets().size() << std::endl;
    }

private:
    QMainWindow * m_content = nullptr;
    std::vector<uncloseableDockWidget *> m_docks;
};

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget * /*parent*/ = nullptr) {
        m_tab = new QTabWidget();
        setCentralWidget(m_tab);
        tab1 * t1 = new tab1();
        m_tab->addTab(t1, "t1");
        tab2 * t2 = new tab2();
        m_tab->addTab(t2, "t2");
        connect(t1, SIGNAL(btClicked()), t2, SLOT(update()));
    }

    ~MainWindow() {

    }
private:
    QTabWidget * m_tab = nullptr;
};

#endif // MAINWINDOW_H

Clicking various times on the "test" button in tab 1, you can see that number of widgets increases.

[Julieng]

Hello SGaist, is the example I provided enough to understand my issue ? Do you think I could get a workaround in order to avoid "leaking" widgets ? Thnanks in advance.

[SGaist]

So it looks like I never submitted my answer, sorry !

I took a look at the internals of QMainWindow and the handling of the QDockWidget "tabification" is more involved than what I thought.

There's no easy workaround per se but there's something I though about: do you really need to delete these dock widgets all the time ? Would a reset of their content be enough ? If you really need to delete them, what about just replacing the widget they contain ? Doing so, you would only have a set of QDockWidget and thus avoid the issue you are currently having.

In any case, I think it would be worth checking the bug report system to see if there's something related and if not, please open a repot providing your small code sample (including the corresponding pro file).

[Julieng]

Thanks SGaist for you answers ! I can change the way I manage the dock widgets (I could just clear the QMainWindow which contains these docks even if I think it will not be as elegant as my first solution). I'll open a bug report as you propose.

[SGaist]

I was rather thinking about cleaning the widgets within the dock widgets. So you keep the number of QDockWidgets constant.