App crashes when moving a DockWidget outside MainWindow

[franku]

Hi There, I have got an application that always crashes when having moved a dockwidget outside the mainwindow. When I leave the dockwidget at its iriginal Place on the left docking area the application will close fine.


App ist build up with this code (Control will instantiate and destroy mainwindow):

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    // app will destroy Control
    // because it becomes Control's 
    // parent object via constructur
    Control::getSingleton(&app);
    int ret = app.exec();
 
    return ret;
} // app Object will be destroyed (and its children)

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

    // app will destroy Control
    // because it becomes Control's 
    // parent object via constructur
    Control::getSingleton(&app);
    int ret = app.exec();

    return ret;
} // app Object will be destroyed (and its children)

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IMHO the ~Control() Destructor will be called by the Application at last, so when finishing the application there will be (the destr. ist definitively called):

/* singleton-private Constructor */
Control::Control(QObject *parent) :
    QObject(parent), 
{
...
    if(!mainWindow)
        mainWindow = new MainWindow();
...
}
 
Control::~Control()
{
...
    if(mainWindow) {
        delete mainWindow; // will delete the ui including dockwidgets
        mainWindow = NULL;
    }
}

/* singleton-private Constructor */
Control::Control(QObject *parent) :
    QObject(parent), 
{
...
    if(!mainWindow)
        mainWindow = new MainWindow();
...
}

Control::~Control()
{
...
    if(mainWindow) {
        delete mainWindow; // will delete the ui including dockwidgets
        mainWindow = NULL;
    }
}

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The Problem now is that when I have App destroying the mainwindow there comes a segmentation fault along - ending always in qwidget.cpp...

....
  else if (!internalWinId() && isVisible()) {
        qApp->d_func()->sendSyntheticEnterLeave(this);
....

....
  else if (!internalWinId() && isVisible()) {
        qApp->d_func()->sendSyntheticEnterLeave(this);
....

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...where the d_func() with its scoped pointer will fail.

But: This only happens, when I have moved the DockWidet "Floating" away from its orignial Place in the main window. If I leave it there, everthing is ok.

As someone may see the stacktrace shows that the Dockwidget will make use of the qapplication d_func(). Am I wrong, or why do at least two parents try to delete the Widget (Mainwindow and App) ?

0	QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::data	qscopedpointer.h	135	0x00ff01e6	
1	qGetPtrHelper<QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> > >	qglobal.h	2314	0x008a63ff	
2	QApplication::d_func	qapplication.h	376	0x00eef9c4	
3	~QWidget	qwidget.cpp	1438	0x008ec5f8	
4	~QDockWidget	qdockwidget.cpp	1181	0x00c51fce	
5	QObjectPrivate::deleteChildren	qobject.cpp	1978	0x6a20f1b0	
6	~QWidget	qwidget.cpp	1476	0x008ec6dc	
7	~QMainWindow	qmainwindow.cpp	329	0x00c82888	
8	~MainWindow	mainwindow.cpp	50	0x004018c0	
9	~Control	control.cpp	83	0x00408feb	
10	QObjectPrivate::deleteChildren	qobject.cpp	1978	0x6a20f1b0	
11	~QObject	qobject.cpp	975	0x6a20d0f9	
12	~QCoreApplication	qcoreapplication.cpp	642	0x6a1fd127	
13	~QApplication	qapplication.cpp	1118	0x008aa05e	
14	qMain	main.cpp	14	0x00401400	
15	WinMain@16	qtmain_win.cpp	131	0x0040e612	
16	main		0	0x0040e338

0	QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::data	qscopedpointer.h	135	0x00ff01e6	
1	qGetPtrHelper<QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> > >	qglobal.h	2314	0x008a63ff	
2	QApplication::d_func	qapplication.h	376	0x00eef9c4	
3	~QWidget	qwidget.cpp	1438	0x008ec5f8	
4	~QDockWidget	qdockwidget.cpp	1181	0x00c51fce	
5	QObjectPrivate::deleteChildren	qobject.cpp	1978	0x6a20f1b0	
6	~QWidget	qwidget.cpp	1476	0x008ec6dc	
7	~QMainWindow	qmainwindow.cpp	329	0x00c82888	
8	~MainWindow	mainwindow.cpp	50	0x004018c0	
9	~Control	control.cpp	83	0x00408feb	
10	QObjectPrivate::deleteChildren	qobject.cpp	1978	0x6a20f1b0	
11	~QObject	qobject.cpp	975	0x6a20d0f9	
12	~QCoreApplication	qcoreapplication.cpp	642	0x6a1fd127	
13	~QApplication	qapplication.cpp	1118	0x008aa05e	
14	qMain	main.cpp	14	0x00401400	
15	WinMain@16	qtmain_win.cpp	131	0x0040e612	
16	main		0	0x0040e338

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Any Comments ?

[The Storm]

QApplication will delete the main window without caring if it is his child or not and I guess that when you delete it yourself when the application object is destructing there is no way for the MainWindow to tell to QApplication that it is deleted and eventually QApplication will try to delete it while looping trough all the objects. So you have 2 choices:

1. Make sure you delete the MainWindow before the destruction of QApplication
2. Let QApplication care for that( this can be tricky depending on your program logic ).