QWidget::style crashes with "Read Access Violation"

[ajaxcrypto]

I have created a custom control (derived from QLabel), and overriden the mouseReleaseEvent where I am emitting certain signals and I need to repolish the widget so that some of the dynamic properties based QSS style gets reflected.

I have a repolish method which is declared as:

void MyWidget::repolish()
{
    auto style = this->style();
    if (style != nullptr)
    {
        style->unpolish(this);
        style->polish(this);
    }
}

The mouse release event handler is:

void MyWidget::mouseReleaseEvent(QMouseEvent * event)
{
    if (isEnabled())
    {
        setPressed(false);
        if (m_canBeToggled)
        {
            setChecked(!m_checked);
        }
        else
        {
            emit clicked();
        }
        repolish();
    }
}

I get a "Read Access Violation" right at the statement auto style = this->style();. Why is this the case?

The attached slot is:
QObject::connect(mywidget, &MyWidget::clicked, [...]{ ... });

[jsulm]

@ajaxcrypto Do you mean you get this error at runtime?

[ajaxcrypto]

Yes at runtime, I figured out the runtime error part. The parent widget was being deleted on the clicked signal emission. Because repolishing happens after the signal, so a repolish on an invalid object was being called.

P.S. - The forum is very prompt!

[SGaist]

Hi,

Why was the parent deleted ?

[ajaxcrypto]

It was because of how the slot was written, which calls some functions which ultimately leads to the deletion. I am now repolishing before emitting the signal because that behavior is required.

[kshegunov]

You should use QObject::deleteLater in this case which will take care of the deletion in a safe manner.