Determine mouse press on dialog or child widget?

Taytoo

I have a draggable dialog with bunch of labels on it. I only want to detect mouse events (down, move, release) on dialog (not on child widgets/labels). QLabel doesn't capture any mouse events resulting in parent/main window receiving those events.

Is there a way to manually Hit-test dialog or have Qlabel widgets accept mouse events so that dialog doesn't receive those?

JonB

@Taytoo
There are several ways to accomplish this. Most involve either subclassing your child widgets or installing an event filter on each one. I'm thinking these would cause you hassle/a lot of work.

One way I would propose which does not involve these is:

/*virtual*/ void Dialog::mousePressEvent(QMouseEvent *mouseEvent) /*override*/
{
    QWidget *w = QApplication::widgetAt(mouseEvent->globalPos());
    if (w != nullptr && w != this)
        qDebug() << "Dialog::mousePressEvent on some other widget" << w << w->objectName();
    else
        qDebug() << "Dialog::mousePressEvent on Dialog";
}

[Note thiis is Qt5. For Qt6 they may have changed to mouseEvent->globalPosition()?]

You can also define an event filter just on the dialog to stop propagation of events on sub-widgets to the dialog, along the lines of:

// this->installEventFilter(this);
bool Dialog::eventFilter(QObject *object, QEvent *event)
{
    QMouseEvent *mouseEvent = dynamic_cast<QMouseEvent *>(event);
    if (mouseEvent)
    {
        QWidget *w = QApplication::widgetAt(mouseEvent->globalPos());
        if (w != nullptr && w != this)
        {
            qDebug() << "Dialog::eventFilter on some other widget" << w << w->objectName();
            return true;
        }
        else
            qDebug() << "Dialog::eventFilter on Dialog";
    }
    return false;
}

You can use this to see whether a mouse event arriving at the QDialog level was actually over some widget inside it. It uses QApplication::widgetAt() which is "slow", but may be fine unless you have very many widgets.

I don't know whether someone else can propose a neater way?

mpergand

@JonB
And what about:
QWidget *QWidget::childAt(int x, int y)
?

JonB

@mpergand
Doesn't do descendent grandchildren etc. ? So by the time you do it recursively what advantages does it offer? And this is only a replacement for the QApplication::widgetAt(), hoping to make it faster, but you would follow one of the approaches above?

Taytoo

@JonB I tried the eventfilter approach. The problem with it is that it layouts and spacers receive input events as well, and its quite a lot of controls that I have to filter through. Is it possible to disable mouse input being sent to all layouts and spacers?