ShortcutOverride

This article may require cleanup to meet the Qt Wiki's quality standards. Reason: Auto-imported from ExpressionEngine. Please improve this article if you can. Remove the {{cleanup}} tag and add this page to Updated pages list after it's clean.

h1. Shortcut Override Events (QKeyEvent)

shortcut: a key combination that triggers an action override: prevent the shortcut action under some circumstances

When the shortcut is about to trigger send shortcut override to the focus item instead. the focus item now has the option to override the shortcut (by accepting the shortcut override event). If the shortcut override is accepted it will be delivered as normal key press to the focus widget. otherwise it will trigger the shortcut action.

Example: A media player uses space for pause/play. This should work everywhere except when searching for music in a line edit.

Example uses of ShortcutOverride in Qt:

QWidgetWindow::handleKeyEvent QComboBoxPrivateContainer::eventFilter

- for enter etc, bad implementation

QWidgetLineControl::processShortcutOverrideEvent(QKeyEvent ke)

- arrow keys, copy paste, …

QMainWindow::event

- to show drag and drop cursor, doesn’t handle event otherwise

QMenu::event

- override arrow and enter keys

QMenuBar::eventFilter

- installs a global event filter (no, really?) temporarily until next key press

h2. Behavior:

In widgets the event is sent to the focus object and then to all it's parent objects. Done by QGuiApplication::notify.

h2. Implementation:

QWindowSystemInterface::tryHandleShortcutEvent

return QGuiApplicationPrivate::instance()->shortcutMap.tryShortcutEvent(w, &qevent);
only used on mac?

QShortcutMap::tryShortcutEvent(QObject *o, QKeyEvent e)

creates actual shortcut events
returns true when shortcut should be overridden (not delivered and not trigger action), even before shortcut is complete
results in QCoreApplication::sendEvent( shortcut overrid event)

Who may call try*ShortcutEvent?

- 

currently:

QNSView: - (void)handleKeyEvent:(NSEvent)nsevent eventType:(int)eventType
m_sendKeyEvent = !QWindowSystemInterface::tryHandleShortcutEvent(focusWindow, timestamp, keyCode, modifiers, text);
is the only user of the QWindowSystem one and thus the duplicate

QGuiApplication:

QGuiApplicationPrivate::instance()->shortcutMap.tryShortcutEvent(focus, static_cast<QKeyEvent'''>(event))

QApplication:

case QEvent::ShortcutOverride:
case QEvent::KeyPress:
case QEvent::KeyRelease:
{
bool isWidget = receiver->isWidgetType();
bool isGraphicsWidget = false;

1. ifndef QT_NO_GRAPHICSVIEW

isGraphicsWidget = !isWidget && qobject_cast<QGraphicsWidget >(receiver);

1. endif

QKeyEvent key = static_cast<QKeyEvent*>(e);
bool def = key->isAccepted();
QPointer<QObject> pr = receiver;
while (receiver) {
if (def)
key->accept();
else
key->ignore();
res = d->notify_helper(receiver, e);
QWidget w = isWidget ? static_cast<QWidget>(receiver) : 0;

1. ifndef QT_NO_GRAPHICSVIEW

QGraphicsWidget gw = isGraphicsWidget ? static_cast<QGraphicsWidget>(receiver) : 0;

1. endif

if ((res && key->isAccepted())

/*
QLineEdit will emit a signal on Key_Return, but
ignore the event, and sometimes the connected
slot deletes the QLineEdit (common in itemview
delegates), so we have to check if the widget
was destroyed even if the event was ignored (to
prevent a crash)

note that we don't have to reset pw while

propagating (because the original receiver will
be destroyed if one of its ancestors is)
*/
|| !pr
|| (isWidget && (w->isWindow() || !w->parentWidget()))

1. ifndef QT_NO_GRAPHICSVIEW

|| (isGraphicsWidget && (gw->isWindow() || !gw->parentWidget()))

1. endif

) {
break;
}

1. ifndef QT_NO_GRAPHICSVIEW

receiver = w ? (QObject)w->parentWidget() : (QObject *)gw->parentWidget();

1. else

receiver = w->parentWidget();

1. endif

}
qt_in_tab_key_event = false;
}
break;