Re: TreeModelFilter + drag and drop

[Kristian Rietveld <kris imendio com>]

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.  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"?


I hope this clears things up a bit.


regards,

-kris.