Qt QGraphicsScene and QGraphicsItem events

Question

I've got some QGraphicsObjects which are dependent of the size of the scene they are on. So my graphics object needs to know when two events occur:

When it is added to the scene
When it's scene is resized

The way I do it now is - create 2 signals in scene's parent: obj_create, scene_resize. And connect them to the slots of the gr.object. It seems to be not the best way. I can't find any event like addedToScene or sceneResized in the QGraphcisItem...

Thanks much.

score 1 · Answer 1 · answered Nov 22 '12 at 19:47

1

I would suggest one of two possible ways: Either subclass QObject in your GraphicsItem and simply use Signal/Slots or define your own interface, lets say IResizableEvent with a resize method. In your GraphicsItem you implement the method with your resize code. When you detect a scene resize in your Scene class, just iterate over all items, cast them to the interface type and call the resize method.

answered Nov 22 '12 at 19:47

Alexander Nassian

517
3
12

Thanks for an answer, but there actually is a special event in QGraphicsItem for that needs... – Kolyunya Nov 22 '12 at 19:55

Kolyunya · Accepted Answer · 2012-11-22T20:25:39.807

I just needed to read the doc little bit accurately... Hope it helps someone...

QVariant        itemChange(GraphicsItemChange change, const QVariant &value)
{

    if (change == QGraphicsItem::ItemSceneHasChanged)
    {

            this->performSomeUpdates();
            QObject::connect(this->scene(),SIGNAL(sceneRectChanged(QRectF)),this,SLOT(sceneRectChanged(QRectF)));

    }

    return QGraphicsItem::itemChange(change, value);

}

Qt QGraphicsScene and QGraphicsItem events

2 Answers2