I do drag&drop between three QTreeWidgets; each tree are diffrent columns:
1) I do "copy" of drag item if d&d is between diffrent trees,
2) I do "move" if d&d is inside the same tree.

After drop I check if dropped item(s) below to dropped tree:
1) if item not below I know that it's "copy" so I add new item to the tree,
2) another way I know it's "move" so swap items positions.

I don't need remember in d&d mime hole dragged items, but only pointer to them, because it can be that some process in my application remove one of dragged item from tree when I do d&d (between time when I drag and time when I drop dragged item). If I know pointer I can check before drop item if it's still in one of trees. That's I need pointer. I thought about QPointer but QTreeWidgetItem is not "a child" of QObject.

I think also about QList<QTreeWidgetItem *>, but I can't read it form stream:

Qt Code: 
  1. QDataStream stream_items
  2. QList<QTreeWidgetItem *> items
  3.  
  4. stream_items << items
  5. stream_items >> items  // can't be
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