Remove QGraphicsEllipseItems

hobbyProgrammer

Hi,

I would like to remove previously added ellipses, but I don't know how to do that.
How can I find these items back so they can be removed?

this is how I draw the ellipses:


void graphicsView::addPoint(QPointF pos)
{
    qv_points << pos;
    QGraphicsEllipseItem *newEllipse = new QGraphicsEllipseItem();

    double x,y;
    QPointF point = pos;
    x = point.x()-2.5;
    y = point.y()-2.5;

    newEllipse->setRect(QRectF(x,y,5,5));
    newEllipse->setBrush(QBrush(Qt::red, Qt::SolidPattern));
    newEllipse->setFlags(QGraphicsEllipseItem::ItemIsMovable | QGraphicsEllipseItem::ItemIsSelectable);

    //add item to scene
    scene->addItem(newEllipse);

    qDebug() << pos;
}

mrjj

Hi
The scene keeps a list of items.
https://doc.qt.io/qt-5/qgraphicsscene.html#items

Something like ( not compiled )
Loop over all items.
Try to cast it to a QGraphicsEllipseItem
if cast is ok, it IS such item
take it from scene
delete it

foreach (QGraphicsItem *item, scene()->items()) {
    QGraphicsEllipseItem*node = qgraphicsitem_cast<https://doc.qt.io/qt-5/qgraphicsscene.html#removeItem*>(item);
    if (!node) // it was NOT an QGraphicsEllipseItem item, so skip it
        continue;
      // its a QGraphicsEllipseItem
      scene()->removeItem(node); // take it out ( wont delete, see docs)
      delete node; // delete it
}

https://doc.qt.io/qt-5/qgraphicsscene.html#removeItem

Notice the ownership comment.

hobbyProgrammer

@mrjj hi thanks! I'll try this and if it works, I'll mark this as solved (and as the right answer)

mrjj

@hobbyProgrammer
It should :)
Please be aware that we cast it as the scene keeps all items as base pointers (QGraphicsItem *) so
we have to check if right type.

Sometimes if having many different types, you can also keep your own list to make it easier to access.

hobbyProgrammer

@mrjj Hi, just realized that this will probably remove all EllipseItems, but I would like to remove them by position.
So if I press the right mouse button, it gives the position to undoAction and then looks which item is placed there.

mrjj

@hobbyProgrammer
Well yes it would if you do the same for all.

But in that use case - you can use
https://doc.qt.io/qt-5/qgraphicsscene.html#itemAt

To ask for a item at some position which i guess you can get from the right click.

hobbyProgrammer

@mrjj it works! thank you so much.

for people watching this:

you can change this:

    QGraphicsEllipseItem*node = qgraphicsitem_cast<QGraphicsEllipseItem*>(item);

into this:

    QGraphicsPolygonItem*node = qgraphicsitem_cast<QGraphicsPolygonItem*>(item);

and it will work for a polygon item

or into this:

    QGraphicsPixmapItem*node = qgraphicsitem_cast<QGraphicsPixmapItem*>(item);

and it will work for pixmapItems
etc.

you can change this line into anything to remove all the object that are that type of graphicsItem