Avoid QGraphicsItem with children from infinite repainting

Question

I have a QGraphicsItem element (subclassesed from QGraphicsItem) that has as child a QGraphicsTextItem.

The problem is that the paint(...) method of the QGraphicsItem is called infinitely.

Here is the paint method from my QGraphicsItem element with the QGraphicsTextItem:

void rectangle_element::paint( QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget )
{
    painter->drawRoundedRect( -10, -10, 80, 40, 5, 5 );
    painter->drawStaticText( -10, -10, QStaticText( "some text" ) );
    text_item->setPlainText( "more text" );
}

I cannot use setCacheMode with other flag than QGraphicsItem::CacheMode::NoCache.

I'm using Qt 5.6.

UPDATE:

• The text_item is a member of the class and it is initialized in the initialization list.

Answer 1

You set the text of text_item in the paint() method of the parent item, which seems to in turn trigger a repaint of the parent, thus creating an infinite loop. Generally, it's not a good idea to change items during paint operations. Keep in mind that the paint() method can be called with a high frequency.

Probably there is some event triggering the need for a text change of text_item, like user interaction, which in turn calls a slot. This is the point where you should set the text. The drawing of the text itself is handled by the QGraphicsTextItem.