Can I get mouse events in a QGraphicsItem?

Almo picture Almo · May 14, 2012 · Viewed 22.1k times · Source

I have subclassed QGraphicsRectItem, and it's not receiving any mouse events. I've seen other questions similar to this say I need to enable mouse tracking, but setMouseTracking is in QWidget, and QGraphicsItem does not appear to be a QWidget.

I've implemented paint, and that's working. In my subclassed QGraphicsView I am getting mouse events.

The docs seem to think I should just override the mousePressEvent function (for example) and I should start getting the events. Whether I forward the mousePressEvent to the superclass of my QGraphicsView or not doesn't seem to make any difference.

Answer

Anthony picture Anthony · May 15, 2012

In your subclassed QGraphicsView, you need to call the default implementations of overridden mouse event methods if you want them to propagate down to the items. For example:

CustomView::mousePressEvent(QMouseEvent *event)
{
    // handle the event as you like

    QGraphicsView::mousePressEvent(event); // then call default implementation
}

If you want to accept hover events, you need to call QGraphicsItem::setAcceptHoverEvents(true);. Otherwise you do not need to enable any particular mouse tracking.

EDIT: Here is a full working example:

#include <QtGui>

class CustomView : public QGraphicsView
{
protected:
    void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "Custom view clicked.";
        QGraphicsView::mousePressEvent(event);
    }
};

class CustomItem : public QGraphicsRectItem
{
protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event)
    {
        qDebug() << "Custom item clicked.";
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    CustomItem item;
    item.setRect(20, 20, 60, 60);

    QGraphicsScene scene(0, 0, 100, 100);
    scene.addItem(&item);

    CustomView view;
    view.setScene(&scene);
    view.show();
    return a.exec();
}