Keyboard key emulation from C++ to QML

RiteshPanchal

I want to emulate keyboard key press event from C++ and that would affect in qml.

In my application i need to operate GUI from keyboard and also from UART.
I am using qml from GUI. and its working great with keyboard. But i want same gui functionalities from UART bytes reception (ex. UP/DOWN uart frame). My UART code works fine. But i am unable to find way to emulate QKeyEvent from C++ file.

main.cpp

int main(int argc, char **argv)
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    UART *uart = new UART(&engine);
    uart->UARTInit();

    engine.load(QUrl(QStringLiteral("qrc:///HomePage.qml")));
    engine.rootContext()->setContextProperty(QLatin1String("uart"), uart);

    return app.exec();
}

UART.cpp

void UART::readRequest()
{
        QKeyEvent key_press(QKeyEvent::KeyPress, Qt::Key_P, Qt::NoModifier);
        QCoreApplication::sendEvent(engine.rootObjects().first(), &key_press);
}

HomePage.qml

ApplicationWindow {
    id: rootWindow
    width: Screen.width
    height: Screen.height
    visible: true
    visibility: Window.FullScreen

    Item {
        id: it
        focus: true

       .
       .

        Keys.onPressed: {
            switch(event.key) {
            case Qt.Key_P:
                gstpipe.play()
                videoview.visible = true
                event.accepted = true;
                break;
           }
      }
   }
}

so i am getting error in "QCoreApplication::sendEvent(engine.rootObjects().first(), &key_press);"
error: 'engine' was not declared in this scope

So how to correctly send QkeyEvent to QML?

RiteshPanchal

I have found one solution for the error: 'engine' was not declared in this scope

UART.h

class UART : public QObject
{
    Q_OBJECT
    QQmlApplicationEngine m_engine;
public:
    explicit UART(QQmlApplicationEngine *engine, QObject *parent = 0);
}

UART.cpp

UART::UART(QQmlApplicationEngine *engine, QObject *parent) :
    QObject(parent), m_engine(engine)
{

}
void UART::readRequest()
{
        QKeyEvent key_press(QKeyEvent::KeyPress, Qt::Key_P, Qt::NoModifier);
        QCoreApplication::sendEvent(m_engine.rootObjects().first(), &key_press);
}

Now i am not getting any error while building.
But when UART request is received and QCoreApplication::sendEvent(m_engine.rootObjects().first(), &key_press); is executed i am getting following error.

ASSERT: "!isEmpty()" in file /usr/include/qt5/QtCore/qlist.h, line 287
The program has unexpectedly finished.

So whats' the missing here?

sierdzio

QQmlApplicationEngine is a QObject, so you are not allowed to copy it!

So, it should help if you declared m_engine as pointer in your UART class:

QQmlApplicationEngine *m_engine;

And then called that pointer from your request:

void UART::readRequest()
{
        QKeyEvent key_press(QKeyEvent::KeyPress, Qt::Key_P, Qt::NoModifier);
        QCoreApplication::sendEvent(m_engine->rootObjects().first(), &key_press);
}

For more information about why QObjects can't be copied, see Qt docs.

RiteshPanchal

@sierdzio Thanks for the reply.
But as i am new to Qt and all. I am asking this question.
If i create new

QQmlApplicationEngine *m_engine;

pointer ? how can i refer it to my original

QQmlApplicationEngine engine;

And i need to pass keyevent to engine .

sierdzio

No, no, you do not need to change anything in your main.cpp, the engine can still be created on stack there.

QQmlApplicationEngine engine;
/// ...
UART *uart = new UART(&engine); // here you pass a reference (pointer) to your UART class - everything is fine

Just changing the UART class as I indicated in my previous post should be enough.

RiteshPanchal

Thanks for the Reply.
I get everything working from below changes.

UART.cpp

UART::UART(QObject *parent) :
    QObject(parent)
{
    m_engine = (QQmlApplicationEngine *)parent;
}

void UART::readRequest()
{
        QKeyEvent key_press(QKeyEvent::KeyPress, Qt::Key_P, Qt::NoModifier);
        QCoreApplication::sendEvent(m_engine->rootObjects().first(), &key_press);
}

UART.h

class UART : public QObject
{
    Q_OBJECT

public:
    explicit UART(QObject *parent = 0);

signals:

protected:

public slots:
    void UARTInit();

private:
    QQmlApplicationEngine *m_engine;

private slots:
    void readRequest();

};

And main.cpp without any change as per your previous reply.

Thanks ... :)