Deleting Ellipse from QGraphicsScene

star673

Hello all,

I would like to make an application which draws Circle randomly. The number of circle should be always specific number. I have created the timer and each timeout I would like to draw a circle. When the number of circle exceed the specigic number, I would like to delete the the circle respectively. The first drawing circle should be deleted firtsly than very timeout I would like to draw new circle. I have used the clear() function but it deleted the graphicsScene.
Here you can see the timeout slot function.

  
void MainWindow::CircleDrawTestSlot(){
 CircleCounter++;

    qreal randomValuePosX = qrand() % (100);
    qreal randomValuePosY = qrand() % (100);

    scene->addEllipse(randomValuePosX,randomValuePosY,40,40,QPen(Qt::red));

    if(CircleCounter>4){
        scene->clear();
        CircleCounter=0;

    }

In the constructor, I have created the timeout mechanism like below.


        timerTarget = new QTimer(this);
        connect(timerTarget,SIGNAL(timeout()),this,SLOT(CircleDrawTestSlot()));
        timerTarget->start(1000);

How should I make this? Thanks in advanced.

JonB

@star673 said in Deleting Ellipse from QGraphicsScene:

I did not create any QGraphicsItem, I just use "addEllipse()" fucntion

Function definition is: QGraphicsEllipseItem *QGraphicsScene::addEllipse().
QGraphicsEllipseItem derives from QGraphicsItem, as do any objects you add onto a QGraphicsScene.

JonB

@star673
QGraphicsScene::clear() clears all QGraphicsItems off the scene, as its name suggests.

You need to call void QGraphicsScene::removeItem(QGraphicsItem *item) on the item/ellipse to remove it. Maintain a FIFO list of the items you add to the scene to know which one to delete next.

star673

@JonB
Thanks for reply. I did not create any QGraphicsItem, I just use "addEllipse()" fucntion to QGraphicsScene. Do I have to create an QGraphicsItem object for each circle?

JonB

@star673 said in Deleting Ellipse from QGraphicsScene:

I did not create any QGraphicsItem, I just use "addEllipse()" fucntion

Function definition is: QGraphicsEllipseItem *QGraphicsScene::addEllipse().
QGraphicsEllipseItem derives from QGraphicsItem, as do any objects you add onto a QGraphicsScene.

star673

@JonB
Thanks. I added like below.

QGraphicsItem *ellipseItem1;
ellipseItem1 = scene->addEllipse(iSecretX,iSecretY,40,40,QPen(Qt::red));

After the process done, I delete like object.

delete ellipseItem1;

It worked.

JonB

@star673 said in Deleting Ellipse from QGraphicsScene:

delete ellipseItem1;

May work, but it's not how I would do it. I would do

delete scene->removeItem(ellipseItem1);

Maybe that is equivalent to delete ellipseItem1;, I don't know.

You have not said anything about/implemented your original:

When the number of circle exceed the specigic number, I would like to delete the the circle respectively.

for which as I said you would need to append() the ellipses created from scene->addEllipse() to a (member variable) FIFO QList<QGraphicsItem *>, so that later you can do something like

delete scene->removeItem(list.takeFirst())