Qt Undo/Redo for moving items - qt

Question

I am implementing undo/redo for move operation on QGraphicsItemGroup in my graphics scene. It works decently for point entity.
My command for move looks like:
class CommandMove : public QUndoCommand
{
public:
CommandMove(QGraphicsItemGroup *group, qreal fromX, qreal fromY,
qreal toX, qreal toY)
{
itemGroup = group;
mFrom = QPointF(fromX, fromY);
mTo = QPointF(toX, toY);
setText(QString("Point move (%1,%2) -> (%3,%4)").arg(fromX).arg(fromY)
.arg(toX).arg(toY));
}
virtual void undo()
{
itemGroup->setPos(mFrom);
}
virtual void redo()
{
itemGroup->setPos(mTo);
}
private:
QGraphicsItemGroup *itemGroup;
QPointF mFrom;
QPointF mTo;
};
My command is pushed to the undo stack as:
if (item.first->scenePos() != item.second)
{
mUndoStack->push(new CommandMove(item.first, item.second.x(),
item.second.y(), item.first->x(),
item.first->y()));
}
item is a QPair defined as:
typedef QPair<QGraphicsItemGroup *, QPointF> item;
Implemenatation for entities like line, circle etc. requires more information as compared to point. eg., start and end points for line. How do I define my command for moving my entities?
Edit
This is my implementation for line:
if (m1)
{
start_p = event->scenePos();
m1 = false;
m2 = true;
}
else if (!m1 && m2)
{
end_p = event->scenePos();
m3 = true;
m2 = false;
}
if (m3)
{
lineItem = new Line(start_p, end_p);
}
Here event is mousePressEvent.
Where do I use setPos to set the position of line?

Answer 1

I think you shouldn't care about all item's peculiarities. You can implement a move command that works well for any item or group of items. This is a modified version of your code.
class CommandMove : public QUndoCommand
{
public:
CommandMove(QGraphicsItem *item, qreal toX, qreal toY)
{
mItem = item;
mFrom = mItem->pos();
mTo = QPointF(toX, toY);
setText(QString("Point move (%1,%2) -> (%3,%4)").arg(mFrom.x()).arg(mFrom.y())
.arg(mTo.x()).arg(mTo,y()));
}
virtual void undo()
{
mItem->setPos(mFrom);
}
virtual void redo()
{
mItem->setPos(mTo);
}
private:
QGraphicsItem* mItem;
QPointF mFrom;
QPointF mTo;
};
I hope this helps.