Respond to application-wide "hotkey" in Qt

Question

I've got a simple Qt app, and I just want to respond to the F12 key, regardless of which widget has focus.

Is there some easy signal or something I can hook in to?

I want to use the F12 key to toggle the main window fullscreen on/off.

Be sure to let the user configure that. There are several other programs that have that exact same feature. — Falmarri, Dec 03 '10 at 00:44
Falmarri: not sure what you mean. Do you mean to let the user decide which hotkey to use to toggle fullscreen mode? Thx. — sidewinderguy, Dec 03 '10 at 00:46

score 32 · Accepted Answer · edited May 02 '14 at 14:24

32

I haven't tried, but here is what I would do :

Create a QShortcut and make sure its context (with setContext()) is Qt::ApplicationShortcut.

shortcut = new QShortcut(QKeySequence(Qt::Key_F12), parent);
shortcut->setContext(Qt::ApplicationShortcut);

Then you just need to connect a slot to the QShortcut::activated() signal.

edited May 02 '14 at 14:24

satanas

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answered Dec 03 '10 at 10:17

Jérôme

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This is one of those things where once you see how to do it, it seems obvious. But before you showed me, I had no clue. ;-) – sidewinderguy Dec 03 '10 at 19:40
It seems to also be easier to use widget wide shortcuts than filtering QKeyEvents – Max13 Mar 03 '15 at 06:42
3

`parent` must be a pointer to existing widget. One can pass `QApplication::desktop()` as `parent`. It is worth to know that modal windows will block shortcuts even with application context. – Marcin Jun 22 '16 at 14:17

score 3 · Answer 2 · answered Nov 18 '20 at 21:57

Setting the shortcut context to Qt::ApplicationShortcut has a serious flaw. It will not work in modal dialogs. So if you want a trully real pan-application-wide shortcut, then you need to override application's notify() method. The alternative is to install event filter for the application object but that I suspect would be slower and requires slightly more code. With notify() it is very simple:

class MyApplication : public QApplication
{
    // TODO: constructor etc.

protected:

bool MyApplication::notify(QObject *receiver, QEvent *event) override
{
    if (event->type() == QEvent::KeyPress)
    {
        auto keyEvent = static_cast<QKeyEvent*>(event);
        if (keyEvent->key() == Qt::Key_F12 && keyEvent->modifiers() == Qt::NoModifiers)
        {
            // TODO: do what you need to do
            return true;
        }  
    }
    return QApplication::notify(receiver, event);
}

}

score 2 · Answer 3 · answered Feb 19 '16 at 23:10

If you have a "central widget" which all of the other widgets are children of, then you can simply set that as the widget argument for QShortcut.

(Python, qt5)

self.centralwidget = QtWidgets.QWidget(MainWindow)

QtWidgets.QShortcut(QtGui.QKeySequence("F12"), self.centralwidget, self.goFullScreen)

I added this as an answer because the shortcut context flag: Qt.ApplicationShortcut did not work for me.

Respond to application-wide "hotkey" in Qt

3 Answers3