Get just lines items from a scene where there are some kind of items.

AlvaroS

Hello everyone.
First of all thanks a lot for helping me and reading this post.

i have a scene where tehera are lines items and a pixmap item.
Then I would like to move just the lines items (not the pixmap item).
My code is like this:

        QList<QGraphicsItem*>a;
        a = scene->items();

    for (int i=0; i<a.size();i++){

        QGraphicsItem* my_item = a.value(i); //Item (i) selected
        QGraphicsLineItem *line_at = qgraphicsitem_cast<QGraphicsLineItem *>(my_item);

        double XStart_line=line_at->line().x1(); //X_start of line i.
        double XEnd_line=line_at->line().x2();
        double YStart_line=line_at->line().y1();
        double YEnd_line=line_at->line().y2();

..... //move the item i

It does not give me any errors but when I run this code fragment it gives me this:
The program has unexpectedly finished.

I think that the problem is that when I run this code I am trying to move every kind of items, not just line items so for that reason it gives me an error.

How can I get information just for Lines items¿?
Because if I get to move just the lines items in FOR it will be solved I think.

Thanks a lot!

jsulm

You should check line_at: is it null or not?
See here: http://doc.qt.io/qt-5/qgraphicsitem.html#qgraphicsitem_cast

QGraphicsLineItem *line_at = qgraphicsitem_cast<QGraphicsLineItem *>(my_item);

If my_item is not QGraphicsLineItem qgraphicsitem_cast will return null and then you dereference null pointer and your program crashes.

AlvaroS

@jsulm It is QGraphics line item just in Lines items.. not in Pixmap... so when iteration FOR is the pixmap iteration, it is crashed... so how can I get just lines items from a scene?

jsulm

As I said just check the pointer:

QList<QGraphicsItem*>a;
a = scene->items();
for (int i=0; i<a.size();i++){
    QGraphicsItem* my_item = a.value(i); //Item (i) selected
    QGraphicsLineItem *line_at = qgraphicsitem_cast<QGraphicsLineItem *>(my_item);
    if (line_at == nullptr)
        continue; // my_item is not a line

   double XStart_line=line_at->line().x1(); //X_start of line i.
   double XEnd_line=line_at->line().x2();
   double YStart_line=line_at->line().y1();
   double YEnd_line=line_at->line().y2();

..... //move the item i

AlvaroS

@jsulm Thanks a lot my friend!!!! That works!!