[Qt-interest] Calling parent Widget slot

[Donal O'Connor]

Hey Justin,

Yeah I changed the constructor the take the derived class type rather than
QWidget base and this worked.

As for creating the label, I done it the correct way so the member variable
of the class gets it, rather than it going on stack.

The sensor/slot way is much cleaner however, so I'll stick to this!

Thanks for your help.

Regards,
Donal

On Thu, Apr 9, 2009 at 4:14 PM, Justin Noel <justin at ics.com> wrote:

> Donal O'Connor wrote:
> > Hi There,
> >
> > I have a custom widget and in it's constructor I pass a parent
> > widget's pointer. The parent is also a custom widget (QWidget) with a
> > custom slot.
> >
> > For exampe:
> >
> > MyCustomWidget(QWidget * parent )
> >    : QWidget(parent)
> > {
> > }
> >
> > In the custom child widget, I now want to call the parent's custom
> > slot from the child. I am doing it this way:
> >
> > (static_cast<ParentWidgetType*>(parentWidget()))->setStatus(tr("Update
> > Status"));
> >
> >
> > The reason for the cast is I need to access the custom slot I've
> > implemented.
> >
>
> If this widget needs a special parent why not enforce that in the
> constructor arguments and keep a QPointer<> wrapped member variable of
> the correct type to access it. It's going to be much much safer than
> static_cast. Depending on the usage here, you could have a signal/slot
> interface to set status, connect it in the ctor and skip the
> member/function calling entirely.
>
> > Now this works fine, until I try and change a member variable in the
> > setStatus(const QString & statusText) method.
> > For example:
> >
> > void ParentWidgetType::setStatus(const QString & statusText)
> > {
> >     m_status->setText(statusText);
> > }
> >
> > This creates a *segmentation fault*, where as
> >
> > void ParentWidgetType::setStatus(const QString & statusText)
> > {
> >      qDebug() << "Hello";
> > }
> >
> > It isn't a case that the m_status isn't created already, it is
> > initialized in the constructor as:
> >
> > m_status = new QLabel("No Status");
> >
> > I also called the slot within the Parent widget and I've no problems.
> >
> > Forgive me if this is more a C++ problem rather than QT.
> >
> > Am I missing something obvious?
> >
>
> It's probably a C++ issue. Make a minimum example and post it if it's
> still an issue. I have a feeling you may have done something like this:
>
> ParentWidgetType::ParentWidgetType()
> {
>    //Wrong! This makes a local variable that shadows the member variable
>    QLabel* m_status = new QLabel("NoStatus");
>
>   //Right! Initializes a member
>   m_status = new QLabel("NoStatus");
> }
>
>
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at trolltech.com
> http://lists.trolltech.com/mailman/listinfo/qt-interest
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20090409/01a13426/attachment.html