如何根据其内容确定QGraphicsTextItem的boundingRect（）？

Question

I am trying to subclass some QGraphicsItem classes:

for QGraphicsTextItem how do I determine the boundingRect() and shape() ?

I am trying to create a boundingRect out of textWidth() and... ?

apparently, in the paint(...) I also have to specify the rectangle I must draw in... and I thought I solved it simply by using

QRectF TextItem::boundingRect() const
{
    qreal w = textWidth(); qreal h = 1000;  // h = ?
//    QRectF rect(QGraphicsTextItem::boundingRect());  // this leads to crash, maybe undefined ?
    QRectF rect(0,0,w,h)
    return rect;
}

void TextItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* /*option*/, QWidget* /*widget*/)
{
    setDefaultTextColor(m_color);
    setPlainText("Hello world");
    QFont f;
    f.setPointSize(200); // calculated
    f.setBold(true);
    painter->setFont(f); // which of this and the next I need...
    setFont(f);          // really seems one of this is not needed
    painter->drawText(QGraphicsTextItem::boundingRect(), Qt::AlignCenter, this->toPlainText());
}

I need to get the boundingRect() out of the actual text - is that possible or already implemented ?

Answer 1

1. why you are subclassing QGraphicsTextItem ? I don't see that you are adding any kind of functionality which is not already done in QGraphicsTextItem .
2. You have quite nice SO reputation but you ask question like a newbie. First describe what is your primary goal! The way you are trying to solve this is secondary thing!
3. read documentation. It quite good. boundingRect has to return smallest possible rectangle which contains whole drawing content of the graphics item. If this value is incorrect you may see some painting artifacts. It is always implemented.
4. it is qiute possible that if you will read documentation of it will turn out that you don't have to subclass anything.