QMdiArea : moving tab issue.

[Satan2K]

Hello everyone,

While designing an application with mdiArea and its tabbed view mode, i have an issue if i set its QTabBar movable : the connexions are not updating to the correct mdi window when moved. If you move the tabs, it will no more focus the correct window.

I'm surely using it wrong, but we never know if it's a bug (or a feature ). I found the same behavior under Qt4.5 (linux), and Qt4.7.1 (windows)

Here's a quick and dirty made example

#include <QApplication>
#include <QtGui>
 
int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
 
    QMdiArea *mdiArea = new QMdiArea();
    mdiArea->setViewMode(QMdiArea::TabbedView);
    mdiArea->findChild<QTabBar*>()->setMovable(true);
 
    QMdiSubWindow *firstTab = mdiArea->addSubWindow(new QTextEdit("i'm the first tab"));
    firstTab->setWindowTitle("first tab");
    QMdiSubWindow *secondTab = mdiArea->addSubWindow(new QTextEdit("i'm the second tab"));
    secondTab->setWindowTitle("second tab");
 
    mdiArea->show();
 
    return app.exec();
}

#include <QApplication>
#include <QtGui>

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

    QMdiArea *mdiArea = new QMdiArea();
    mdiArea->setViewMode(QMdiArea::TabbedView);
    mdiArea->findChild<QTabBar*>()->setMovable(true);

    QMdiSubWindow *firstTab = mdiArea->addSubWindow(new QTextEdit("i'm the first tab"));
    firstTab->setWindowTitle("first tab");
    QMdiSubWindow *secondTab = mdiArea->addSubWindow(new QTextEdit("i'm the second tab"));
    secondTab->setWindowTitle("second tab");

    mdiArea->show();

    return app.exec();
}

To copy to clipboard, switch view to plain text mode 

Thanks for your help, have a good day,

[high_flyer]

Without dwelling to long in your code, the follwing is not clear to me:

mdiArea->findChild<QTabBar*>()->setMovable(true);

mdiArea->findChild<QTabBar*>()->setMovable(true);

To copy to clipboard, switch view to plain text mode 

You call this right after creating the MDI area, when it has no children yet.. actually I would say this line should crash, since the returned pointer should be null...
You should call this after you have added your children to the MDI.
Even if you would call this line in the right place have a look at the docs about it:

If there is more than one child matching the search, the most direct ancestor is returned. If there are several direct ancestors, it is undefined which one will be returned. In that case, findChildren() should be used.

[Satan2K]

When the viewMode is set to tabbed view, a MDI area always has a QTabBar widget.

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
 
    QMdiArea *mdiArea = new QMdiArea();
    mdiArea->setViewMode(QMdiArea::TabbedView);
    mdiArea->dumpObjectTree();
    mdiArea->show();
 
    return app.exec();
}

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

    QMdiArea *mdiArea = new QMdiArea();
    mdiArea->setViewMode(QMdiArea::TabbedView);
    mdiArea->dumpObjectTree();
    mdiArea->show();

    return app.exec();
}

To copy to clipboard, switch view to plain text mode 

QMdiArea::
    QWidget::qt_scrollarea_hcontainer
        QScrollBar::
        QBoxLayout::
    QWidget::qt_scrollarea_vcontainer
        QScrollBar::
        QBoxLayout::
    QWidget::
    QTabBar:: // <= Here
        QToolButton::
        QToolButton::

QMdiArea::
    QWidget::qt_scrollarea_hcontainer
        QScrollBar::
        QBoxLayout::
    QWidget::qt_scrollarea_vcontainer
        QScrollBar::
        QBoxLayout::
    QWidget::
    QTabBar:: // <= Here
        QToolButton::
        QToolButton::

To copy to clipboard, switch view to plain text mode 

And, as i can see on the doc, there's no other way to get access to its QTabBar widget.

[Satan2K]

So is it the correct behavior, or should i report it as a bug?

In the meantime, i changed completely the part using QMdiArea to an new object inheriting from QTabWidget, and i destroy its child widget when a tab is requested to be removed. (tabCloseRequested(int) to a custom slot)

tabObject->widget(index)->deleteLater();
tabObject->removeTab(index);

[high_flyer]

So is it the correct behavior, or should i report it as a bug?

I didn't have time to test this, so I don't know.
Hopefully someone else can comment on this too.

[Ev_genus]

In the meantime, i changed completely the part using QMdiArea to an new object inheriting from QTabWidget, and i destroy its child widget when a tab is requested to be removed. (tabCloseRequested(int) to a custom slot)

tabObject->widget(index)->deleteLater();
tabObject->removeTab(index);

Thanks a lot for your question. I've tried to make my own mdi-style widget with QTabBar but have many problems with destruction. First of this two lines is exactly what I need.

About QMdiArea. Since you hacked it to find mysterious QTabBar inside, you can't be sure about stable behavior in future. So I think this situation is a feature. (Or feature-lack in QMdiArea interface )

[norobro]

So is it the correct behavior, or should i report it as a bug?

Looks like a fix has been submitted for review: link

[Satan2K]

haha great, so I don't have to worry about reporting it. Thanks

Thanks a lot for your question. I've tried to make my own mdi-style widget with QTabBar but have many problems with destruction. First of this two lines is exactly what I need.

It's quite simple if you inherit from a QTabWidget. Here's the test example i quickly designed.

class UI_TabWidget : public QTabWidget
{
    Q_OBJECT
 
    public :
            UI_TabWidget(QWidget *pParent = 0);
            void openTab();
 
    private slots :
            void closeTab(int iTabIndex);
};

class UI_TabWidget : public QTabWidget
{
    Q_OBJECT

    public :
            UI_TabWidget(QWidget *pParent = 0);
            void openTab();

    private slots :
            void closeTab(int iTabIndex);
};

To copy to clipboard, switch view to plain text mode 

UI_TabWidget::UI_TabWidget(QWidget *pParent) : QTabWidget(pParent)
{
    this->setMovable(true);
    this->setTabsClosable(true);
    QObject::connect(this, SIGNAL(tabCloseRequested(int)), this, SLOT(closeTab(int)));
}
 
void UI_TabWidget::openTab()
{
    //Here's a quick test widget
    QTextEdit *pTextEdit = new TextEdit();
    //Attaching it to a new tab
    this->addTab(pTextEdit, "test");
}
 
void UI_TabWidget::closeTab(int iTabIndex)
{
    this->widget(iTabIndex)->deleteLater();
    this->removeTab(iTabIndex);
}

UI_TabWidget::UI_TabWidget(QWidget *pParent) : QTabWidget(pParent)
{
    this->setMovable(true);
    this->setTabsClosable(true);
    QObject::connect(this, SIGNAL(tabCloseRequested(int)), this, SLOT(closeTab(int)));
}

void UI_TabWidget::openTab()
{
    //Here's a quick test widget
    QTextEdit *pTextEdit = new TextEdit();
    //Attaching it to a new tab
    this->addTab(pTextEdit, "test");
}

void UI_TabWidget::closeTab(int iTabIndex)
{
    this->widget(iTabIndex)->deleteLater();
    this->removeTab(iTabIndex);
}

To copy to clipboard, switch view to plain text mode 

Feel free to attach a custom made widget in openTab too, and you'll be able to access its member with

myCustomWidget *pWidget = dynamic_cast <myCustomWidget*>(this->widget(iTabIndex));

myCustomWidget *pWidget = dynamic_cast <myCustomWidget*>(this->widget(iTabIndex));

To copy to clipboard, switch view to plain text mode 

Then you'll be able to make custom states to check before closing

if (!pWidget->m_bAllowedToClose)
   //...

if (!pWidget->m_bAllowedToClose)
   //...

To copy to clipboard, switch view to plain text mode 

Have fun ;-)