Casting Parent Object Not Working QT 5.2.1

creeveshft

Hello, I am trying to cast the parent widget in the child widget.

this is how I create the ControlBar object inside a member function of class MainTabs

@
ControlBar * cb = new ControlBar(this);
ui->mainTabControl->addTab(cb,"t");
@

I then cast the parentWidget to type MainTabs

@
MainTabs* mt = qobject_cast<MainTabs*>(parentWidget());
if (mt ==0)
{
qDebug() << "error with the cast";
}
@

The cast fails.

not sure why?

[edit: added missing coding tags @ SGaist]

SGaist

Hi,

@ControlBar * cb = new ControlBar(this);@

I suppose that MainTabs is the "this" here, right ?

If so:

@ui->mainTabControl->addTab(cb,"t");@

now there's a change of parent thus your cast will fail.

Anyway, it's always a Bad Idea (™) to start casting the parent widget inside a child widget. If the child widget needs to know its parent for some reason then there's generally a design flow somewhere. e.g. You need the value of a property of the parent to set something in your child widget then you should rather give that child a setter or a constructor with a parameter that the parent will call with the right value.

Think of this: you want to change your parent widget for something else, right now you also have to alter the code of your child widget.

Hope it helps

creeveshft

What I am trying to do is change the text of the tabs from within the ControlBar class.

I can not think of a way to get a reference to the QTabWidget from ControlBar. I guess I could pass the QTabWidget to the constructor.

I need to know the index of the tab in order to change its text, so I planned to use QTabWidget.indexOf( ControlBar*); and then I have the index.

is the preferred way to pass an instance of the parent to the child?

thanks

creeveshft

I got it to work by passing ui->mainTabControl to the constructor of my ControlBar class.

I guess passing an instance of what you need to the constructor is the preferred way?

creeveshft

this is what is in my MainTabs class
@
void MainTabs::AddNewTab()
{

ControlBar * cb = new ControlBar(this,ui->mainTabControl);

}

@

This is what is in my ControlBar class

@
int currentIndex = _mainTabControl->indexOf(this);

_mainTabControl->setTabText(currentIndex,title);
@

SGaist

Do you plan to change the title several times ?