Is it necessary to call the event handler of the base class in subclasses?

Question

Say I have QWidget::keyPressEvent(QKeyEvent *e) reimplemented in my subclass.

Is it necessary to call the base class' implementation at the end of it?

Example:

MyWidget::keyPressEvent(QKeyEvent *e)
{
    // my event handler...

    // now call parent event handler, necessary?
    QWidget::keyPressEvent(e);
}

If so, what's the point of doing that?

score 6 · Accepted Answer · answered Feb 02 '13 at 22:11

6

If you do not act on the event you should always pass the event to the base class' implementation as it may act on it, or there may be an event filter installed for it. The default implementation of QWidget for instance closes popup widgets if the user presses Esc. So, to be sure not to break any event handling, always pass on events to the base class, unless you act on them.

answered Feb 02 '13 at 22:11

Daniel Hedberg

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What if the user tries to enhance a widget by adding a few functions to it *and* calling the default implementation as well? – Petross404 Apr 29 '22 at 19:49
1

That's perfectly fine. Do your thing, and then call the base class handler. – Daniel Hedberg Nov 15 '22 at 12:58

Is it necessary to call the event handler of the base class in subclasses?

1 Answers1