CODEWITHSUNDEEP
c++qtqt4
Thomas Andrees
Thomas Andrees

Reputation: 251

Access to parent in Qt

I try to access parent from a child. Parent and Child class inherits QWidget Let see:

//parent.h

public:
child* h_child = nullptr; //pointer to child - now i can control child in parent methods


//method in parent.cpp
h_child = new child(); //show child window
h_child->show(); //show next window

And child

//child.cpp in child method
 parent_class *sth = qobject_cast<parent_class*>(parentWidget());

if (sth == NULL){
    QMessageBox::warning(this, "error !", "error!");
}

And ofc i saw 'error'

  1. I try to replace parentWidget() with this->parent(). // result the same

  2. I try to run child instance like that:

    h_child = new child(this); //show child window

But when i try to use h_child->show() the window which is showed is 'broken' (i have window in window(child window in parent window , without child window frame) - it looks illegibly)

So how can i access to parent methods and variables ?

Upvotes: 1

Views: 3963

Answers (3)

lazycoder
lazycoder

Reputation: 336

As the others already stated, you need to set the parent of the child in the constructor. If you pass this as parent and your widget/window looks broken afterwards, it is probably a layout problem. Do your widgets have a layout and do you add the child to the layout of the parent?

Upvotes: 0

eferion
eferion

Reputation: 902

To set the parent of a widget you can do this:

widget = new Widget( parent );

or this:

widget->setParent( parent );

of course if you try to show a widget without parent, it is shown with their own window border.

When you implement new widget you shall "propagate" parent pointer form constructor:

class Widget : public QWidget
{
  public:

    Widget( QWidget* parent ) : QWidget( parent )
    { }
};

If you forget this step, base Qt widget doesn't notice the assignment and this widget will not have valid parent.

Upvotes: 1

Paul
Paul

Reputation: 13238

After you create your child do you set your parent to be the parentWidget? Normally, when you create QWidget you pass parent to the constructor, but in your code I see that child() constructor does not have any parameters. That's why parentWidget() returns NULL, you just don't set it anywhere.

Upvotes: 2

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