[Qt-interest] Drag & Drop of hierachical items in a TreeView

[Stephen Kelly]

Daniel Price wrote:

> I'm trying to figure how to do drag and drop editing of hierarchical data
> within an QAbstractItemModel-derived adaptor within a QTreeView.
> 
> Single items with no children seem to work fine (I'm only interested in
> moving data, not copying it). However if I move an item with children, the
> children are lost and I'm not sure how I can preserve them as the
> dropMimeData() virtual only gives me the mime data and drop target.

It is odd that the children are lost. How are you doing the actual move?
If you are using Qt4.6, try the beginMoveRows/endMoveRows api. It should not 
be necessary to reconstruct the entire tree if you do that.

> 
> I can think of same ways around this but I don't know what the 'best
> practice' solution would be:
> 
> 1)      Encode the QModelIndex of the original item into the mime data
> (QDataStream) and use it to recursively iterate through and reconstruct
> the tree in the drop location (it seems that the source items are not
> removed until after dropMimeData() is called so the index should remain
> valid).
> 
> 2)      Cache the source model index somewhere when a drag is initiated
> (mimeData()?) and do the above.
> 
> Any suggestions? Has anyone got this working?

The way we do this in akonadi is by encoding a url of the item in the 
mimedata. The url can be used to get the internal data object (Collection or 
Item), and a move operation is kicked off. The move in the model is done 
when we get notified that the move is complete.

see dropMimeData here:
http://websvn.kde.org/trunk/KDE/kdepimlibs/akonadi/entitytreemodel.cpp?view=markup

and monitoredCollectionMoved here:
http://websvn.kde.org/trunk/KDE/kdepimlibs/akonadi/entitytreemodel_p.cpp?view=markup

All the best,

Steve.

> 
> 
> Daniel Price
> Software Engineer
> FXhome Limited
> 
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