Question

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 1

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();
}