Question

Greetings,

for one of my applications I’m trying to implement an “Edit” menu. This menu usually has the standard-entries Undo, Cut, Copy and Paste.

This menu is not there by default, and users seem to expect it especially on Mac OS X.

Is there a an easier way of implementing this, without doing so in every widget manually? Since most widgets have the copy/paste/undo mechanism already implemented via shortcuts, I’d like to provide a few simple menu actions that call them as well.

The actions should call whatever widget has the focus first, then they should pass the events upwards the object chain, I guess.

I’m using Qt 4.6 on Windows, Linux and Mac OS X.

Thanks!

Answer 1

It’s easy enough to accomplish half of the necessary functionality. Just create the Edit menu, along with the necessary QActions (copy/paste/undo/etc.) in your main window class and connect them to slots. In the slots, emulate the correct key press and release events (e.g. Ctrl+C for Copy) and send them to the currently focused widget. In code, something like this:

MainWindow::MainWindow(...)
{
    ...
    connect( actionCopy, SIGNAL( triggered()), SLOT( copy()));
    ...
}
...
void MainWindow::copy()
{
    QWidget* focused = QApplication::focusWidget();
    if( focused != 0 )
    {
        QApplication::postEvent( focused,
                                 new QKeyEvent( QEvent::KeyPress,
                                                Qt::Key_C,
                                                Qt::ControlModifier ));
        QApplication::postEvent( focused,
                                 new QKeyEvent( QEvent::KeyRelease,
                                                Qt::Key_C,
                                                Qt::ControlModifier ));
}

Of course, this is quite a hack. You need to modify the code for each target platform, changing the keyboard shortcuts to the correct ones, and it might happen that a widget that receives focus does something quiet unexpected with Ctrl+C. The worst downside in this method, in my opinion, is that you cannot properly control the enabled state of the Edit menu items. It is not possible to query from a generic widget whether a copy or paste operation would be possible or not.

I am unable to find a real solution to this problem – and would be surprised to find out that one exists – as the copy/paste functionality is generally hidden inside the class’ code and not exposed through any standard set of signals/slots. After tonight’s experiments with the functionality, I have decided to just forget having an Edit menu from my application and expect the users to know the keyboard shortcuts, or use the context sensitive menus.