[Interest] type casting 5 levels down no error but not proper

[Sujan Dasmahapatra]

class MainWindow : public QMainWindow

{

Q_OBJECT

public:

                MainWindow(QWidget parent=0);

}; 

 

class CDataPage : public QDialog

{

Q_OBJECT

public:

                CDataPage(MainWindow *parent=0);

}

 

class CTabWidget : public QTabWidget

{

   Q_OBJECT

public:

                CTabWidget(CDataPage *parent=0);

} ;

 

CTabWidget::CTabWidget(CDataPage *parent) : QTabWidget(parent)

{

}

 

 

 

class CSheet : public QWidget

{

Q_OBJECT

Public:

CSheet(CTabWidget  *parent=0);

~CSheet();

};

 

CSheet::CSheet(CTabWidget *parent) : QWidget(parent)

{

 

}

 

MainWindow *mainwin = new MainWindow;

CDataPage *dataPage = new CDataPage(mainwin);

CTabWidget *tabWid = new CTabWidget(dataPage);

CSheet *sheet = new CSheet(tabWid);

 

 

Is this correct type castting???

 

MainWindow *mainwinhandle = qobject_cast<MainWindow * >(
sheet->parent()->parent()->dataPage()->parent())->statusBar()->showMessa
ge(tr("A new plot being added"),5000);

 

It's crashing...

 

 

From: Carel Combrink [mailto:carel.combrink at gmail.com] 
Sent: Wednesday, April 25, 2012 12:42 PM
To: Sujan Dasmahapatra
Cc: interest at qt-project.org
Subject: Re: [Interest] type casting 5 levels down no error but not
proper

 

If your requirement is " Please help me getting the mainwindow handle "
then try something like this:

 

    bool continueSearching = true;
    QWidget* widgetParent = NULL;
    QMainWindow* mainWindow = NULL;
    QWidget* currentWidget = this;
    while(continueSearching == true) {
        widgetParent = qobject_cast<QWidget*>(currentWidget->parent());
        if(widgetParent != NULL) {
            currentWidget = widgetParent;
            mainWindow = qobject_cast<QMainWindow*>(currentWidget);
            if(mainWindow != NULL) {
                continueSearching = false;
            }
        } else {
            continueSearching = false;
        }
    }
    if(mainWindow != NULL) {
        mainWindow->statusBar()->showMessage(tr("A new plot being
added!!"),5000);
    }
 

The idea is to loop through all of the parents of the widgets until one
is a QMainWindow. The other approaches can also work like a global
mainwindow or something. This can be used to get the QMainWindow of any
QWidget.

 

Note: I have briefly tested it and it seems to work. It might have
problems but the basic idea is there. 

 

Regards,

 

On Tue, Apr 24, 2012 at 2:42 PM, Sujan Dasmahapatra
<sdh at lmwindpower.com> wrote:

Thanks Diego and Konstantin for your valuable inputs. I am now doing
qobject_cast for all of them, please check the code snippet below, now
it's crashing at tabWid step. It's giving QASSERT failure. The failure
is happening in the following file

 

//qscopedpointer.h at the following line QASSERT(d)

  inline T *operator->() const

    {

        Q_ASSERT(d); //this line it's crashing.

        return d;

    }

 

[code]

QWidget *wid  = qobject_cast<QWidget *>(parent());

CSheet *sheet = qobject _cast<CSheet *>(wid->parent());

QScrollBar *scrollBar = qobject _cast<QScrollBar *>(sheet->parent());

CTabWidget *tabWid = qobject _cast<CTabWidget *>(scrollBar->parent());
// Here it is crashing, QSSERT(d)  failure

CDataPage  *dataPage = qobject _cast<CDataPage *>(tabWid->parent());

MainWindow *mainwin = qobject _cast<MainWindow *>(dataPage->parent());

mainwin->statusBar()->showMessage(tr("A new plot being added!!"),5000);

[/code]

 

CTabWidget is a custom class derived from QTabWidget.

 

Please help me getting the mainwindow handle.  Thanks for your reply.

 

 

 

 

From: Diego Iastrubni [mailto:diegoiast at gmail.com] 
Sent: Tuesday, April 24, 2012 5:41 PM
To: Sujan Dasmahapatra
Cc: interest at qt-project.org
Subject: Re: [Interest] type casting 5 levels down no error but not
proper

 

 

On Tue, Apr 24, 2012 at 2:58 PM, Sujan Dasmahapatra
<sdh at lmwindpower.com> wrote:

please check the code snippet below:

 

[code]

QWidget *wid  = reinterpret_cast<QWidget *>(parent());

CSheet *sheet = reinterpret_cast<CSheet *>(wid->parent());

QScrollBar *scrollBar = reinterpret_cast<QScrollBar *>(sheet->parent());

CTabWidget *tabWid = reinterpret_cast<CTabWidget
*>(scrollBar->parent());

CDataPage  *dataPage = reinterpret_cast<CDataPage *>(tabWid->parent());

MainWindow *mainwin = reinterpret_cast<MainWindow
*>(dataPage->parent());

mainwin->statusBar()->showMessage(tr("A new plot being added!!"),5000);
//[I][SIZE=7]Here it is crashing[/SIZE][/I]

[/code]

 

 

You meant 

 

[code]

MainWindow *mainwin = dynamic_cast<MainWindow>(dataPage->parent());

if (mainwin!=NULL) {

   // do your thing

}

[/code]

 

Or use qobject_cast as recommended. This will be faster then
dynamic_cast.

 


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