Re: GTK TreeView control in Windows (DND issue)

[dieterv <dieterv optionexplicit be>]

On Tue, 13 Sep 2011 11:18:50 +0100, John Emmas wrote:
> Thanks Dieter.  I was particularly interested to read that apparently
> this did once work.  Also, the fact that it can be made to work after
> a fashion by using 'gtk_drag_source_set() / dest_set()' instead of 
> the
> official 'gtk_tree_view_enable_model_drag_source() / drag_dest()'.  I
> just tried that (in C++) and I can see why someone might think that
> but to be honest, I'm not convinced it's the solution.

It's not the solution but was proposed as a workaround until a proper
solution is found.

> What I did notice though is that regardless of whether you use
> 'gtk_tree_view_enable_model_drag_source()' or 'gtk_drag_source_set()'
> there's a problem with the context action.  In function
> 'gtk_drag_button_release_cb()' (gtkdnd.c) there's a section that 
> looks
> like this:-
>
> if ((info->context->action != 0) && (info->context->dest_window != 
> NULL))
> {
>         gtk_drag_end (info, event->time);
>         gtk_drag_drop (info, event->time);
> }
> else
> {
>         gtk_drag_cancel (info, GTK_DRAG_RESULT_NO_TARGET, 
> event->time);
> }
>
> Normally, 'info->context->action' would be whatever action you'd set
> it to (GDK_ACTION_MOVE / GDK_ACTION_COPY / GDK_ACTION_ASK etc).  But
> by the time the code reaches that point the action data seems to have
> gotten lost somewhere.  For a TreeView control (in gtk-win32)
> 'info->context->action' is always zero.   Consequently, the rest of
> the process always fails and 'gtk_drag_cancel()' gets called.   This
> is what's aborting the drop part and it's true, whichever method you
> use to set up the drag source.

I think you're on to something here...

> If nobody already knows what's wrong I'll see if I can look into this
> and find some more information but it won't be this week.  Probably
> early next week with a bit of luck.  I'm amazed that this hasn't been
> solved already though. It's been a problem for a very long time.  I'd
> be happy to collaborate with one of the devs though, if that would
> help speed things along.

Most likely nobody has had the time to look into it. Sadly, there's not
that many people left working on the win32 port, so all the help we
can get is *most welcome*!

I'd be glad to help out where I can with this, especially because the
solution we find for gtk-2.24 might also help gtk-3, where DnD 
currently
crashes horribly (for example gtk3-demo's "Icon View>Editing and
Drag-and-Drop" demo).

But be aware I'm not an expert on GDK's win32 backend either.

Thanks,
Dieter