Hello , I have a problem, that QGraphicsItem doesn't update, when I'm calling update(). This is what I'm doing:
CircleItem.cpp
Qt Code: 
  1. void CircleItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
  2. {
  3.     RectItem->SetBackGround();
  4.     QGraphicsItem::mouseMoveEvent( event );
  5. }
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RoundRectItem.cpp
Qt Code: 
  1. void RoundRectItem::SetBackGround()
  2. {
  3.     ChangeBackground = true;
  4.     update();
  5. }
  6.  
  7. void RoundRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  8. {
  9.     QRectF rec = QRectF( QPoint( 0,0 ), boundingRect().size() / 2 );
  10.  
  11.     roundRect = QRectF(rec.adjusted(-rec.height() / 2, 0, rec.height()/2, 0));
  12.  
  13.     roundRect.moveTo( boundingRect().center().x() - roundRect.width() / 2,
  14.                       boundingRect().center().y() - roundRect.height() / 2 );
  15.  
  16.     if( !ChangeBackground )
  17.         painter->setBrush( backBrush );
  18.     else
  19.         painter->setBrush( QBrush( Qt::blue ) );
  20.  
  21.     painter->setPen( QColor( 255,255,255 ) );
  22.  
  23.     painter->drawRoundedRect(roundRect, roundRect.height() / 2, roundRect.height() / 2 );
  24.  
  25. }
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And after this, roundrect doesn't update its background.