Qt update() doesn't work

问题

I have a problem , that update() function in QGraphicsItem doesn't work. What I want to do is , when I move circle , other QGraphicsItem( in the mean time roundrect ) changes color. This is a example, what I want to do:

circle.cpp:

void CircleItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    // RoundRect Object
    RectItem->SetBackGround();
    QGraphicsItem::mouseMoveEvent( event );
}

RoundRect.cpp:

void RoundRectItem::SetBackGround()
{
    ChangeBackground = true;
    update();
}

void RoundRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QRectF rec = QRectF( QPoint( 0,0 ), boundingRect().size() / 2 );

    roundRect = QRectF(rec.adjusted(-rec.height() / 2, 0, rec.height()/2, 0));

    roundRect.moveTo( boundingRect().center().x() - roundRect.width() / 2,
                      boundingRect().center().y() - roundRect.height() / 2 );

    if( !ChangeBackground )
        painter->setBrush( backBrush );
    else
        painter->setBrush( QBrush( Qt::blue ) );

    painter->setPen( QColor( 255,255,255 ) );

    painter->drawRoundedRect(roundRect, roundRect.height() / 2, roundRect.height() / 2 );
}

So the question is, how can I make this update() work right.

回答1:

You are invoking the update() method of QGraphicsItem. You should call the update() of the QGraphicsView you are working with. For example you can keep your QGraphicsView as a member class of your item like:

QGraphicsView * parent;

And call it's update method when you want the changes take place like:

void RoundRectItem::SetBackGround()
{
    ChangeBackground = true;
    parent->update();
}

来源：https://stackoverflow.com/questions/22900106/qt-update-doesnt-work

标签

c++

qgraphicsview

qgraphicsitem