Should I use KeyPressEvent or QAction to implement keypresses? - qt

Question

In Qt, either implementing keyPressEvent or creating a QAction and assigning it a key combination allow me to act based on the keyboard.
Which of these methods is generally preferred?

Answer 1

You should use QAction whenever the same event that is triggered by the key sequence you want may be triggered through other ways like from a menu, toolbar or other buttons. This way you can use the same action on several widgets that should do the same trick.
Excerpt from QAction doc:
The QAction class provides an abstract
user interface action that can be
inserted into widgets.
In applications many common commands
can be invoked via menus, toolbar buttons, and
keyboard shortcuts. Since the user
expects each command to be performed
in the same way, regardless of the
user interface used, it is useful to
represent each command as an action.

Answer 2

I'd prefer to overwrite the keyPressEvent. I don't like the idea of a QAction "lying around somewhere". Just overwrite the keyPressedEvent. I usually do it with a switch-case in which I check the pressed key. Just don't forget to call the keyPressEvent of the base class if you don't want to disable the standard behaviour of a key. Additionally you can check if a "modifier" is pressed while a keyPressEvent occurs. (e.g. Shift or Ctrl). IMHO for general purposes overwriting the keyPressEvent is better than creating invisible, secret actions, unless you want your application to contain all those actions visible for the user.
void my_widget::keyPressEvent( QKeyEvent* p_event )
{
bool ctrl_pressed = false;
if( p_event->modifiers() == Qt::ControlModifier )
{
ctrl_pressed = true;
}
switch( p_event->key() )
{
case Qt::Key_F:
focus_view();
break;
case Qt::Key_I:
if( ctrl_pressed )
{
toggle_interface();
}
else
{
QWidget::keyPressEvent( p_event );
}
break;
case Qt::Key_Return: // return key
case Qt::Key_Enter: // numpad enter key
update_something();
break;
default:
QSpinBox::keyPressEvent( p_event );
}
}

Answer 3

Would depend on what you need it for.
Is it for a menu like action that may be triggered by a menu, button, toolbar too, then go for the QAction. Especially if this action should work all over your program, not only in a single widget.
Is it more like a local activity in a single widget (say for example controlling movement in a game), I would use the keypress event.