connecting lines?

Hi, I can draw a line between two points and if the point moves the line moves too.
But now I would like to draw a second line between the first point and another one. This works, but then the line isn't connected to the points.
I don't know what's wrong, can somebody help me?

Code:

---

void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *e)
{
pos=e->scenePos();
end=e->scenePos();
item = new EllipseItem(pos.x(), pos.y(),10,10);
item2 = new EllipseItem(end.x(), end.y(),10,10);
item->setFlags(QGraphicsItem::ItemIsMovable);
item2->setFlags(QGraphicsItem::ItemIsMovable);
 
if(e->button() == Qt::LeftButton)
{
	if(itemAt(pos))
	{QGraphicsScene::mousePressEvent(e); }
 
        else
	{addItem(item);
	linie = new LineItem(item,item2);
	QObject::connect(item, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
	QObject::connect(item2, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
	addItem(linie);
	}
}
 
if(e->button() == Qt::RightButton)
{
	if(itemAt(pos))
	{
	linie = new LineItem(item,item2);
	QObject::connect(item, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
	QObject::connect(item2, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
	addItem(linie);
	}
	else
	{ QGraphicsScene::mousePressEvent(e); }
}
}
 
void GraphicsScene::mouseMoveEvent(QGraphicsSceneMouseEvent *e)
{
if((e->buttons()==Qt::LeftButton) || (e->buttons()==Qt::RightButton))
	{item2->setPos(e->scenePos());
	item2->update();
	linie->updatePosition();
	linie->update();
	}
 QGraphicsScene::mouseMoveEvent(e);
}

---

No idea whats wrong? :(

Could you prepare a minimal compilable example reproducing the problem?

Code:

---

void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *e)
      {
      pos=e->scenePos();
      end=e->scenePos();
      item = new EllipseItem(pos.x(), pos.y(),10,10);
      item2 = new EllipseItem(end.x(), end.y(),10,10);
      item->setFlags(QGraphicsItem::ItemIsMovable);
      item2->setFlags(QGraphicsItem::ItemIsMovable);
 
      if(e->button() == Qt::LeftButton)
      {
          if(itemAt(pos))
          {QGraphicsScene::mousePressEvent(e); }
 
           else
          {
          addItem(item);
          linie = new LineItem(item,item2);
          QObject::connect(item, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
          QObject::connect(item2, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
          addItem(linie);
      //here I draw the item and a line, which is connected to the item and item2, this works
          }
      }
 
      if(e->button() == Qt::RightButton)
      {
          if(itemAt(pos))
          {
          linie = new LineItem(item,item2);
          QObject::connect(item, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
          QObject::connect(item2, SIGNAL(positionchanged()), linie , SLOT(updatePosition()));
          addItem(linie);
//here should appear the second line (without creating a new item(startpoint) and a new item2, which is connected, too.
//but when I move item or item2 , the line doesn't move
//this doesn't work
          }
          else
          { QGraphicsScene::mousePressEvent(e); }
      }
      }
 
void GraphicsScene::mouseMoveEvent(QGraphicsSceneMouseEvent *e)
      {
      if((e->buttons()==Qt::LeftButton) || (e->buttons()==Qt::RightButton))
          {item2->setPos(e->scenePos());
          item2->update();
          linie->updatePosition();
          linie->update();        
          }
       QGraphicsScene::mouseMoveEvent(e);
      } 
 
void GraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *e)
{
QGraphicsScene::mouseReleaseEvent(e);
end=e->scenePos();
 
	if(itemAt(end))
	{QGraphicsScene::mouseReleaseEvent(e);}
	else
	{addItem(item2);} //here I draw item2
}

---

Do you know how I could connect the item to the line?

This is not a compilable example reproducing the problem. It's two methods of some nondefined class. I was asking for something I can compile (qmake && make) and run to see the problem myself.

sorry, here is the first part

and here th second

Edit (wysota): - next time please attach an archive instead of standalone files

can you see what's missing ?

The problem is in your release event:

Code:

---

void GraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *e)
 
{
 
QGraphicsScene::mouseReleaseEvent(e);
end=e->scenePos();
 
	if(itemAt(end))
	{
	QGraphicsScene::mouseReleaseEvent(e);
 
	}
 
	else
	{
	addItem(item2);
 
	}
}

---

If you are releasing the mouse on the first line, itemAt() returns a valid pointer, thus an item is not added (the base implementation is called instead).

In general we'd do it differently. Either create a single item consisting of a line with two ellipses or create two ellipses and use QGraphicsItem::itemChange() to react on updates of items' geometry to snap the lines connecting the ellipses into place.

Something like this:

Code:

---

QVariant itemChange ( GraphicsItemChange change, const QVariant & value ) {
        if (change==QGraphicsItem::ItemPositionHasChanged) {
            QLineF li = lineItem->line();
            if(isStartPoint()) li.setP1(pos());
            else li.setP2(pos());
            lineItem->setLine(li);
        }
        return QGraphicsEllipseItem::itemChange(change, value);
}

---

Thanks, but can you help me to realize?!

Code:

---

QVariant itemChange ( GraphicsItemChange change, const QVariant & value ) {
              if (change==QGraphicsItem::ItemPositionHasChanged) {
                  QLineF li = lineItem->line();  
                    //the class LineItem is LineItem(item1,item2)
                    //so I have to write something like QLineF li = lineItem(item1,item2)->line(); 
                    //but in the class ellipseitem I can't creat two ellipses?!
                  if(isStartPoint()) li.setP1(pos());
                  else li.setP2(pos());
                  lineItem->setLine(li);
              }
              return QGraphicsEllipseItem::itemChange(change, value);
      }

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