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Error using foreach

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  • F Offline
    F Offline
    frnklu20
    wrote on last edited by
    #4

    is there someway to tell to the computer that the object is member of a subclass too?
    like scene->item is for sure a QGraphicsItem, but is also a DiagramItem that is a subclass of DiagramItem

    i don't know if i was clear

    1 Reply Last reply
    0
    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #5

      As already suggested, just cast it in the loop. Otherwise you have to add your own method to your class that returns that list of your subclass.

      Interested in AI ? www.idiap.ch
      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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      • F Offline
        F Offline
        frnklu20
        wrote on last edited by
        #6

        how can i do this?

        sorry, i don't what it is

        aha_1980A 1 Reply Last reply
        0
        • F frnklu20

          how can i do this?

          sorry, i don't what it is

          aha_1980A Offline
          aha_1980A Offline
          aha_1980
          Lifetime Qt Champion
          wrote on last edited by
          #7

          @frnklu20

          Could be something like this:

          foreach(QGraphicsItem *item,scene->items()){
              DiagramItem *itempos = (DiagramItem *)item;
              ...
          }
          

          Regards

          Qt has to stay free or it will die.

          1 Reply Last reply
          3
          • F Offline
            F Offline
            frnklu20
            wrote on last edited by
            #8

            oh thanks :))

            1 Reply Last reply
            1
            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #9

              You also have qgraphicsitem_cast. Take a look at the documentation. There's on additional thing you have to do before using it.

              Interested in AI ? www.idiap.ch
              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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              3
              • F Offline
                F Offline
                frnklu20
                wrote on last edited by frnklu20
                #10
                                          if(item->type()==DiagramItem::Type && itempos->type()==DiagramItem::Type
                                                  && itempos!=item){
                                          DiagramItem *itempos = (DiagramItem *)item;
                                          DiagramItem *item = (DiagramItem *)item;
                
                                          DiagramItem *startItem = qgraphicsitem_cast<DiagramItem *>(item);
                                          DiagramItem *endItem = qgraphicsitem_cast<DiagramItem *>(itempos);
                                          Arrow *arrow = new Arrow(startItem, endItem);
                                          arrow->setColor(scene->myLineColor);
                                          item->addArrow(arrow);
                                          itempos->addArrow(arrow);
                                          arrow->setZValue(-1000.0);
                                          scene->addItem(arrow);
                                          }
                

                like this? the program keep crashing when i do this

                aha_1980A 1 Reply Last reply
                0
                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #11

                  You're not checking whether these pointers are nullptr.

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • F Offline
                    F Offline
                    frnklu20
                    wrote on last edited by
                    #12
                               if(item->type()==DiagramItem::Type && itempos->type()==DiagramItem::Type
                                     && itempos!=item && item!=nullptr && itempos!=nullptr){
                    

                    like this? the program still crashes

                    but if i remove the lines:

                                 item->addArrow(arrow);
                                 itempos->addArrow(arrow);
                    

                    it doesn't crashes but it doesn't draw a line between the objects neither

                    1 Reply Last reply
                    0
                    • F frnklu20
                                                if(item->type()==DiagramItem::Type && itempos->type()==DiagramItem::Type
                                                        && itempos!=item){
                                                DiagramItem *itempos = (DiagramItem *)item;
                                                DiagramItem *item = (DiagramItem *)item;
                      
                                                DiagramItem *startItem = qgraphicsitem_cast<DiagramItem *>(item);
                                                DiagramItem *endItem = qgraphicsitem_cast<DiagramItem *>(itempos);
                                                Arrow *arrow = new Arrow(startItem, endItem);
                                                arrow->setColor(scene->myLineColor);
                                                item->addArrow(arrow);
                                                itempos->addArrow(arrow);
                                                arrow->setZValue(-1000.0);
                                                scene->addItem(arrow);
                                                }
                      

                      like this? the program keep crashing when i do this

                      aha_1980A Offline
                      aha_1980A Offline
                      aha_1980
                      Lifetime Qt Champion
                      wrote on last edited by
                      #13

                      @frnklu20 Where does it crash exactly? Use a debugger and step through to find the faulty line.

                      Qt has to stay free or it will die.

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                      0
                      • F Offline
                        F Offline
                        frnklu20
                        wrote on last edited by
                        #14

                        what i'm trying to do is drawing a line that is QGraphicsItem between 2 objects that already exist using the DiagramScene example form Qt

                        diagramscene.cpp

                        void DiagramScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
                        {
                               
                            if (mouseEvent->button() != Qt::LeftButton)
                                return;
                        
                            DiagramItem *item;
                            switch (myMode) {
                                   case InsertLine:
                                    line = new QGraphicsLineItem(QLineF(mouseEvent->scenePos(),
                                                                mouseEvent->scenePos()));
                                    line->setPen(QPen(myLineColor, 2));
                                    addItem(line);
                                    break;
                        }
                        }
                        
                        void DiagramScene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
                        {
                            if (myMode == InsertLine && line != 0) {
                                QLineF newLine(line->line().p1(), mouseEvent->scenePos());
                                line->setLine(newLine);
                            } else if (myMode == MoveItem) {
                                QGraphicsScene::mouseMoveEvent(mouseEvent);
                            }
                        }
                        
                        void DiagramScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
                        {
                            if (line != 0 && myMode == InsertLine) {
                                QList<QGraphicsItem *> startItems = items(line->line().p1());
                                if (startItems.count() && startItems.first() == line)
                                    startItems.removeFirst();
                                QList<QGraphicsItem *> endItems = items(line->line().p2());
                                if (endItems.count() && endItems.first() == line)
                                    endItems.removeFirst();
                        
                                removeItem(line);
                                delete line;
                        
                        
                                if (startItems.count() > 0 && endItems.count() > 0 &&
                                    startItems.first()->type() == DiagramItem::Type &&
                                    endItems.first()->type() == DiagramItem::Type &&
                                    startItems.first() != endItems.first()) {
                                    DiagramItem *startItem = qgraphicsitem_cast<DiagramItem *>(startItems.first());
                                    DiagramItem *endItem = qgraphicsitem_cast<DiagramItem *>(endItems.first());
                                    Arrow *arrow = new Arrow(startItem, endItem);
                                    arrow->setColor(myLineColor);
                                    startItem->addArrow(arrow);
                                    endItem->addArrow(arrow);
                                    arrow->setZValue(-1000.0);
                                    addItem(arrow);  #and here it draws the line
                                    arrow->updatePosition()
                        }
                        }
                        

                        and i what i want to draw a line between 2 objects but not by creating a line with insertline mode

                        mainwindow.cpp

                        void MainWindow::infoItem()
                        {
                            foreach (QGraphicsItem *item, scene->selectedItems()){#the item object is the selected one
                               if (item->type() == DiagramItem::Type){
                        
                        if(item->data(0)=="Carga"){#carga is type of object
                        CargaDialog *carga=new CargaDialog;
                                      carga->setModal(true);
                        #its a dialog that contains a combo box, an the items of this combo box are the items that are in the screen that are not cargas
                        #and after select an item in the combo box, it will draw a line between the carga and the item selected
                        
                        if(carga->getItem()!="Selecione um barramento" && carga->getItem()!=(item->data(1)).toString()){
                                          #getItem() is a function that return the name of item selected in the combo box
                                          item->setData(4,carga->getItem());
                                          foreach(QGraphicsItem *itempos,scene->items()){
                                              if(itempos->data(1)==carga->getItem())
                                             #i use the data(1) slot of the objects to store the name of each object, so now i looking for the QGraphicsItem that have the same name as the item selected
                                              {
                        
                                                  if(item->type()==DiagramItem::Type && itempos->type()==DiagramItem::Type
                                                          && itempos!=item && item!=nullptr && itempos!=nullptr){
                                                  DiagramItem *itempos = (DiagramItem *)item;
                                                  DiagramItem *item = (DiagramItem *)item;
                        
                                                  DiagramItem *startItem = qgraphicsitem_cast<DiagramItem *>(item);
                                                  DiagramItem *endItem = qgraphicsitem_cast<DiagramItem *>(itempos);
                                                  Arrow *arrow = new Arrow(startItem, endItem);
                                                  arrow->setColor(scene->myLineColor);
                                                  item->addArrow(arrow);#if i remove these two lines, the program doesn't crash but it doesn't draw a line on the screen
                                                  itempos->addArrow(arrow);
                                                  arrow->setZValue(-1000.0);
                                                  scene->addItem(arrow);
                                                  arrow->updatePosition();
                                                  }
                                              }
                        

                        i don't know why this is going on, because it's exactaly the same this that is done in diagramscene.cpp

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                        0
                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #15

                          As already suggested, start your application with the debugger and check the stack trace.

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                          1 Reply Last reply
                          1
                          • fcarneyF Offline
                            fcarneyF Offline
                            fcarney
                            wrote on last edited by
                            #16

                            @frnklu20 said in Error using foreach:

                            (DiagramItem *)item;

                            Should this be done this way?

                            DiagramItem *itempos = dynamic_cast<DiagramItem*>(item);
                            // check if itempos is null
                            

                            This gives us some more type safety no?

                            C++ is a perfectly valid school of magic.

                            1 Reply Last reply
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