Using Hover Events

问题:

I am having trouble capturing the hover enter and hover leave events in a QGraphicsRectItem.

I have subclassed this object, and reimplemented the hover enter and hover leave handlers... or at least I think I have. I also set accepts hover event to true in the constructor.

The event is never fired, however. Breakpoints inside the handlers are never hit.

Here is the class:

#include "qhgraphicsrectitem.h"

QhGraphicsRectItem::QhGraphicsRectItem(QGraphicsRectItem *parent) :
    QGraphicsRectItem(parent)
{
    setAcceptHoverEvents(true);
    setAcceptsHoverEvents(true);
}

void QhGraphicsRectItem::hoverEnterEvent(QGraphicsSceneHoverEvent *event) {
    oldBrush = brush();
    setBrush(QBrush(QColor((oldBrush.color().red() + (0.5 * (255-oldBrush.color().red()))),(oldBrush.color().green() + (0.5 * (255-oldBrush.color().green()))),(oldBrush.color().blue() + (0.5 * (255-oldBrush.color().blue()))))));
}

void QhGraphicsRectItem::hoverLeaveEvent(QGraphicsSceneHoverEvent *event) {
    setBrush(oldBrush);
}

What is it that I am doing wrong?

回答1:

Did you mark your hoverEnterEvent and hoverLeaveEvent as virtual? If you didn't, the events could be triggering but the QGraphicsItem is handling the event instead.

class QhGraphicsRectItem : public QGraphicsItem
{
    ...
    virtual void hoverEnterEvent(QGraphicsSceneHoverEvent *event);
    virtual void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);
}

回答2:

Is your item located under a QGraphicsItemGroup?

I had this exact same issue until I found this quote:

"A QGraphicsItemGroup is a special type of compound item that treats itself and all its children as one item (i.e., all events and geometries for all children are merged together)."

(Look here: http://qt-project.org/doc/qt-4.8/qgraphicsitemgroup.html)

What this means is that QGraphicsItemGroup calls setHandlesChildEvents(true).

I fixed my issue by calling parentItem->setHandlesChildEvents(false) on any (and all) groups located above my item to capture hover events. Poof! The events began showing up in the virtual callbacks you mention.