Space key doesn't trigger keyPressEvent

[Cruz]

As long as child widgets do not handle key events themselves...

I don't know why you assume you have full information about my application, but to set this straight, the application contains widgets that do their own key event handling in undesired ways. For example, QSliders handle the arrow keys when they have focus. But the arrow keys have a different function in my program and it's important that the arrow keys do what they do no matter where the focus is. I would have to subclass QSlider or filter events or do whatever acrobatics is necessary to stop them from handling keys I need for something else. This goes for a number of widgets, all of which would require individual attention.

Then there are also lovely cases where more than one widget needs to do something in response to a single key press, no matter where the focus is. As far as I can tell this is also not something that "proper" key handling is prepared for, because the widget that has the focus and handles the event, consumes the event too. So I would have to "hack" something to circumvent the default event handling mechanism and to forward the event to multiple widgets. Just because there are predefined Qt ways to accomplish this, it doesn't make it any less complex and cumbersome.

The grabKeyboard() hack solves it all with one line and puts all keyboard handling in one place. It's easy to find, to understand, and to maintain.

[wysota]

The grabKeyboard() hack solves it all with one line and puts all keyboard handling in one place. It's easy to find, to understand, and to maintain.

I still think this is a hack. The sort of "offcial" way of providing your own event handling is to reimplement QCoreApplication::notify().

If grabKeyboard() works for you then that's fine. However if you are only after modifying some keys globally then using either of the two mentioned solutions (notify() or application event filter) is a more clean approach without getting you into a God Object design anti-pattern. Simply delegate the "custom" behaviours to a dedicated place and leave everything else to the default mechanism.

E.g.:

bool XXX::eventFilter(QObject *object, QEvent *event) {
  if(event->type() != Qt::KeyPressEvent) return false;
  QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
  if(keyEvent->key() == Qt::Key_Left && object != myMainWindow) {
    myMainWindow->keyPressEvent(keyEvent); // or do whatever else you'd like, e.g. event->ignore() letting it propagate until the main window
    return true; // eat the left arrow key event
  }
  return false;
}

bool XXX::eventFilter(QObject *object, QEvent *event) {
  if(event->type() != Qt::KeyPressEvent) return false;
  QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
  if(keyEvent->key() == Qt::Key_Left && object != myMainWindow) {
    myMainWindow->keyPressEvent(keyEvent); // or do whatever else you'd like, e.g. event->ignore() letting it propagate until the main window
    return true; // eat the left arrow key event
  }
  return false;
}

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