QGraphicsItem::setToolTip does not work

[Nadia]

Hi,

I have an item dierived from QGraphicsItem.

and I want a toolTips for this item

hotPoint::hotPoint(const QPointF& hotPoint)
{
    setAcceptHoverEvents(true);
    setToolTip("An important value");
    point = hotPoint;
}

hotPoint::hotPoint(const QPointF& hotPoint)
{
    setAcceptHoverEvents(true);
    setToolTip("An important value");
    point = hotPoint;
}

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what else I should do to make toolTip shown?