Error using foreach

[frnklu20]

I'm having a problem using the foreach an I don't know why I am wrong

If i do something like this, it works just fine

foreach(QGraphicsItem *item,scene->items()){

But if I do something like this(Remembering that QGrphicsItem is parent of Diagram Item):

foreach(DiagramItem *itempos,scene->items()){

it gives me the following error

mainwindow.cpp:166:40: error: cannot initialize a variable of type 'DiagramItem *' with an lvalue of type 'QGraphicsItem *const'
qglobal.h:1029:21: note: expanded from macro 'foreach'
qglobal.h:1021:10: note: expanded from macro 'Q_FOREACH'

how can i fix it?

[SGaist]

Hi,

Is DiagramItem a subclass of QGraphicsItem ?
If so, then just cast the pointer to it in the loop.

[frnklu20]

Hi,

yes it is!

Now i think what is the problem

foreach(QGraphicsItem *item,scene->items()){

i defined scene as DiagramScene *scene, and when i do scene->items it returns a QGraphicsItem :( i don't know if i can fix it

[frnklu20]

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

[SGaist]

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.

[frnklu20]

how can i do this?

sorry, i don't what it is

[aha_1980]

@frnklu20

Could be something like this:

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

Regards

[frnklu20]

oh thanks :))

[SGaist]

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

[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

[SGaist]

You're not checking whether these pointers are nullptr.

[frnklu20]

           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

[aha_1980]

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

[frnklu20]

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

[SGaist]

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

[fcarney]

@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?