qgraphicsscene remove item but sometime still in view

choujayylyxm

someone metion :https://www.qtcentre.org/threads/28749-Qt-4-6-GraphicsView-items-remove-problem

choujayylyxm

This post is deleted!

SGaist

Hi,

@choujayylyxm said in qgraphicsscene remove item but sometime still in view:

No one reply?!

No need to resort to bold fonts and such questions. A friendly ping is welcome though. This is a voluntary driven forum. People answering here do it on their own time and might not live in the same timezone as you. And it's also possible that no one has an answer for you.

In any case, you should provide a minimal compilable example that reproduces your issue.
You should also test your code against a more recent version of Qt, 5.9.5 is more than outdated. Qt 5.15 is the current LTS. Providing the platform your code runs on would also be good idea.

choujayylyxm

Ok，I understood.Sorry for that.
Here is a simple example:

   //click a button to switch line and run below code
  //  a QGraphicsView scene()->addItem(m_chart);
  //replace a new line
  QLineSeries * tmp = static_cast<QLineSeries *>(m_chart->series()[0]);
  QList<QPointF> dataPointList;
  //set new axis range
  m_chart->axisX()->setRange(0,dataVec[dataVec.size()-1].x());
  m_chart->axisY()->setRange(-qAbs(yMax)*1.2f, qAbs(yMax)*1.2f);
  tmp->replace(dataPointList);
  
  
  //delete last line a flag(circle)item in the qchart ，m_calloutsList is keep flags list
  for(auto& item : m_calloutsList[nDataIndex])
  {
      //item.prepareGeomtryChange //try it not work
      scene()->removeItem(item);
  }
  //add current line flag item
  for(auto& item2 : m_calloutsList[nDataIndex])
  {
  //item2.prepareGeomtryChange //try it not work
      scene()->addItem(item2);
  }

SGaist

Please provide a minimal compilable example that shows the behavior.

choujayylyxm

@SGaist OK,I upload a minimal compilable example for github
github link

Is it okay? It base on qt example callout

choujayylyxm

@SGaist Fine,I keep working on it.

SGaist

Did you try to call hide on your items before removing them from the scene ?

One thing: there's no need to make the QGraphicsItemObject. A simple QGraphicsRectItem is enough for your purpose.

Ketan__Patel__0011

try to After

remove the item from your qgraphicsscene

        scene()->removeItem(YOURITEM_OBJECT);
        ui->graphicsview->viewport()->update();
        ui->graphicsview->update();
        ui->graphicsview->show();

StudentScripter

@SGaist Having a question regarding calling hide cause i encounter similar problems.
In my scene i want to add some items when another item is clicked, but when i unselect the other items the items added shall be removed aswell.

NOW as i figured when just calling remove onto the other items the programm crashes cause there is still the flag "isVisible" given back on remove.

Is it in this case fine to just case setVisible(false) and than scene()->removeItem(), because than it don't crashes. But im not sure if thats proper way to do it or is it just a whacky fix.

Here is my code that draws the items when the Owner item is clicked:

void ITMHandleDraw::drawHandlesIfNecessary()
{
    //qDebug() << "DrawHandles" << ShouldDrawHandles << ownerItem->isSelected();
    if(!ownerItem){
        qWarning() << "ITMHandleDraw : No ownerItem set. Not drawing any\
                      handle. Please call setOwnerItem on your ITMHandleDraw subclass";
                      return;
    }

    if(ownerItem->isSelected()){
        drawHandles();

    }else if(!ownerItem->isSelected()){
        handlesAddedToScene = false;

        // Ensure handles are removed from the scene before deletion
        //Remove the handles
        foreach (ITMHandleLogic * ITMHandleLogic, handleList) {
           // ITMHandleLogic->setVisible(false);

            ITMHandleLogic->scene()->removeItem(ITMHandleLogic);
            qDebug() << ITMHandleLogic->isVisible();
        }
            qDeleteAll(handleList);
            handleList.clear();

    }

}

jsulm

@StudentScripter said in qgraphicsscene remove item but sometime still in view:

foreach (ITMHandleLogic * ITMHandleLogic, handleList) {

Is this your real code?! Because it can't even compile.
I also don't get what this line is supposed to do:

ITMHandleLogic->scene()->removeItem(ITMHandleLogic);

JonB

@jsulm said in qgraphicsscene remove item but sometime still in view:

foreach (ITMHandleLogic * ITMHandleLogic, handleList) {

Is this your real code?! Because it can't even compile.

Don't know if you maybe thought this was a for, but it's a foreach and compiles fine? As does e.g.

QList<QString *> QStringList;
foreach (QString * QString, QStringList) {

Unfortunately the OP has a predilection for naming variables identically to their types, which is not helpful but (at least in this case) works fine.

I also don't get what this line is supposed to do:

ITMHandleLogic->scene()->removeItem(ITMHandleLogic);

Given ITMHandleLogic which is a pointer to a QGraphicsItem this gets to the QGraphicsScene from it via QGraphicsItem::scene() to call QGraphicsItem::removeItem(ITMHandleLogic). Alternatively the OP could just have called delete ITMHandleLogic to delete and remove (per Qt internal code for QGraphicsItem destructor which removes from scene).

JonB

@StudentScripter said in qgraphicsscene remove item but sometime still in view:

calling remove onto the other items the programm crashes cause there is still the flag "isVisible" given back on remove.

Is it in this case fine to just case setVisible(false) and than scene()->removeItem(), because than it don't crashes.

First, why do you care about isVisible() or setVisible() at all in your situation? Once you removeItem() the QGraphicsItem will no longer be shown on the scene/view so it's not relevant.

But given that you want to use it. After removeItem() the item no longer belongs to the scene in any way. I would guess that QGraphicsItem::visible() needs to access the scene from the item in order to do whatever calculations are required for "visibility". But for a removed item the scene is probably "undefined" (or maybe nullptr) and hence it "crashes". Do not call any methods on a QGraphicsItem once it has been removed from the scene. If you really want to set/test visibility do so before removeItem().