I also figured out an another way to figure out the row numbers of the moving items from before and after the move, which is based on indexFromItem() like your suggestion:

@
void MyTreeWidget::dropEvent(QDropEvent event)
{
// get the list of the items that are about to be dropped
QList<QTreeWidgetItem> dragItems = selectedItems();

// find out their row numbers before the drop
QList<int> fromRows;
QTreeWidgetItem *item;
foreach(item, dragItems) fromRows.append(indexFromItem(item).row());

// the default implementation takes care of the actual move inside the tree
QTreeWidget::dropEvent(event);

// query the indices of the dragged items again after the drop
QList<int> toRows;
foreach(item, dragItems) toRows.append(indexFromItem(item).row());

// notify subscribers in some useful way
emit itemsMoved(fromRows, toRows);

}
@

You could also extend the QTreeWidget with a class that holds the current QModelIndex (cur) of the current pointer and the previous position (pre).

When you do the internal movement set pre =cur, cur = indexFromItem(QTreeWidgtItem).
Do a check to see if pre != cur or if pre!= some default value, then emit(moved_item(pre, cur)) and set pre to cur or a default value.

@
void ProjectTree::dropEvent(QDropEvent *event)
{
// retrieve the target of the drop
QTreeWidgetItem *target = itemAt(event->pos());
DropIndicatorPosition dropPos = dropIndicatorPosition();
// when the drop indicator points above an item, then this is the
// correct one, otherwise, replace target item with the one below
if (dropPos == BelowItem) target = itemBelow(target);

// get list of selected items from the tree; these are the dragged
// items
QList<QTreeWidgetItem*> dragItems = selectedItems();

// default implementation takes care of the actual move
QTreeWidget::dropEvent(event);
// notify subscribers of item move in some user-friendly way
emit itemsMoved(...)
}
@

The way I see it, since QTreeWidget has signals like itemClicked(), itemChanged() etc., it should also have itemMoved(from, to) which would let me react to the move easily.

When you reimplemented the dropEvent() are you emitting a signal? If there isn't a signal you like you can always make your own.

i'm not sure if this will help you at all: http://qt-project.org/wiki/Qt_for_beginners_Signals_and_slots_2