如何在QML应用程序中安装和使用Qt C ++编写的事件过滤器

Question

I have a situation where I need to add keyboard shortcuts to an application that is mainly comprised of a QtQuick user interface. The version of Qt Quick is unfortunately locked to Qt5.3 and Shortcuts (the way we need them) were only introduced in Qt5.5 and Qt5.7 respectively.

So, as a solution, I wrote an event filter that functions similarly to QShortcut (can't use QShortcut, hence the event filter).

Does anybody know how to install and use this eventfilter in QML?

Answer 1

One way would be to expose a singleton type to QML:

#include <QtGui>
#include <QtQml>

class ShortcutListener : public QObject
{
    Q_OBJECT

public:
    ShortcutListener(QObject *parent = nullptr) :
        QObject(parent)
    {
    }

    Q_INVOKABLE void listenTo(QObject *object)
    {
        if (!object)
            return;

        object->installEventFilter(this);
    }

    bool eventFilter(QObject *object, QEvent *event) override
    {
        if (event->type() == QEvent::KeyPress) {
            QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
            qDebug() << "key" << keyEvent->key() << "pressed on" << object;
            return true;
        }
        return false;
    }
};

static QObject *shortcutListenerInstance(QQmlEngine *, QJSEngine *engine)
{
    return new ShortcutListener(engine);
}

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qmlRegisterSingletonType<ShortcutListener>("App", 1, 0, "ShortcutListener", shortcutListenerInstance);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

#include "main.moc"

main.qml :

import QtQuick 2.5
import QtQuick.Window 2.2

import App 1.0

Window {
    id: window
    width: 640
    height: 480
    visible: true

    Component.onCompleted: ShortcutListener.listenTo(window)
}

If you have several different listeners, you could also do it declaratively by adding an object property to ShortcutListener that it would install an event filter on when set.

For more info, see Integrating QML and C++ .