Re: TreeModelFilter + drag and drop

[Yann Leboulanger <asterix lagaule org>]

Kristian Rietveld wrote:
> On Sat, Nov 17, 2007 at 10:54:45PM +0100, Yann Leboulanger wrote:
>> I'd like to use Drag and drop on a treeview that gets data in a
>> TreeModelFilter. Of course at the begining I got this error:
>>
>> [snip]
>>
>> So what I understood is that I had to write a drag_drop handler and put
>> my code there instead of in the drag_data_received handler and finish by
>> stopping the propagation of the event. Am I right?
> 
> You could indeed go that way and write a drag_drop handler.  Since you
> will have to use gtk_drag_get_data() to retrieve the actual data that
> was dropped, you will probably end up implementing your own handler for
> drag_data_received as well (because gtk_drag_get_data() will trigger
> drag_data_received).  Note that the default implementations of both of
> those handlers in GtkTreeView are not trivial at all; they contain logic
> to handle several special corner cases (drops on empty views, etc).
> 
>> If so, the problem is that drag_drop handler don't get selection_data
>> and info parameters. Is there a way to get them? For selection_data this
>> can be a global variable, but for info, I don't see how to know if the
>> drop happend on a row, between 2 rows ...
> 
> GtkTreeView just uses the (x, y) coordinates to figure out where you
> dropped.  To determine if the user dropped in between or on a row, it
> just calculates where on the row the user dropped (vertically of
> course).  If it was close to the row's edge, it will drop before or
> after; if the drop was closer to the middle of the row it will drop
> into.  See gtk_tree_view_get_dest_row_at_pos().
> 
> Instead of replicating this tree view code, it might be well easier to
> derive a new class from GtkTreeModelFilter and implement the
> GtkTreeDragDest here.  See GtkTreeModelSort for an example how the
> GtkTreeDragDest implementation would look like, it should be very
> similar.

I just had a look at gtktreemodelfilter.c in gtk+-2.10.14, and I don't
see what has to be done. gtk_tree_model_filter_row_draggable,
gtk_tree_model_filter_drag_data_get,
gtk_tree_model_filter_drag_data_delete functions have code, and there is
no more function in tree gtktreemodelsort.c about TreeDragSource interface.
What did I miss?

> At some point in the future the GtkTreeModelFilter might
> implement the GtkTreeDragDest interface by default, but all kinds of
> interesting problems turn up, such as:
> 
>   ROW   1
>   [row 2]
>   [row 3]
>   ROW   4
> 
> say rows 2 and 3 are hidden.  The tree view will only display row 1 and
> 4.  Say the user drops a row in between row 1 and 4, where would you
> insert it in the original model, where row 2 and 3 do exist and are
> "visible"?

My "root" model has a sort function, so that should handle this case.

> 
> 
> I hope this clears things up a bit.
> 
> 
> regards,
> 
> -kris.
> 
-- 
Yann