# Extending GTK+ Classes in Ruby (revisited)

**URL:** <https://www.ruby-forum.com/t/extending-gtk-classes-in-ruby-revisited/148108>\
**Category:** Ruby-Gnome 2\
**Created:** [September 9, 2008, 12:33pm UTC](https://www.ruby-forum.com/t/extending-gtk-classes-in-ruby-revisited/148108 "2008-09-09T12:33:19Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Andrew\_SSTownley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d07c76/32.png) [@Andrew\_SSTownley](https://www.ruby-forum.com/u/Andrew_SSTownley)\
**Post date:** [September 9, 2008, 12:33pm UTC](https://www.ruby-forum.com/t/extending-gtk-classes-in-ruby-revisited/148108/1 "2008-09-09T12:33:19Z")

</div>

Hi,

I’m trying to figure out if it’s possible to create a custom cell  
renderer using a Ruby class. Digging through the source, I found the  
type\_register example, and that does allow me to provide default  
handlers for the editing signals, but in order to do my custom renderer,  
I need to override some of the methods in the base class.

According to examples I’ve found, you can do this sort of thing with the  
Python bindings, but I don’t see how you can do it from the Ruby ones.  
I saw the following thread on the mailing list back in 2003  
([http://sourceforge.net/mailarchive/message.php?msg\_id=20030912092726.GA2014%40intersect-uk.co.uk](http://sourceforge.net/mailarchive/message.php?msg_id=20030912092726.GA2014%40intersect-uk.co.uk)))  
as well as (  
[http://sourceforge.net/mailarchive/message.php?msg\_id=14e8de370603312339ne957094y5a45753e65e419e8%40mail.gmail.com](http://sourceforge.net/mailarchive/message.php?msg_id=14e8de370603312339ne957094y5a45753e65e419e8%40mail.gmail.com)).  
I’ve also been looking through how it’s implemented in the C source, but  
I haven’t used C GLib/GTK+ in years, and I’ve never done anything other  
than read about extending Ruby in C apart for adding a missing method to  
the Ruby goocanvas bindings (patch to follow at some stage).

Does anyone have any idea how item #1 in the 2003 email message can be  
accomplished? I _really_ don’t want to have to write my custom cell  
renderer in C, then wrap it in Ruby just so I can render one set of  
cells in one table which represents about .000001 of the functionality  
of what I’m trying to write.

I’m sure that solving this problem would also be very useful to the  
general community for cell renderers and view models (which are the main  
reasons you’d need to do something more sophisticated than the signal  
handling already there).

In the old threads, the problem of GLib interfaces vs. Ruby was also  
raised. However, I’d think there should be an easy solution for this.  
Something like the following seems to be a good trade-off:

class MyRenderer \< Gtk::CellRenderer  
type\_register  
implements\_interface(Gtk::foo)  
implements\_interface(Gtk::bar)

…  
end

or, you could do something like

class MyRenderer \< Gtk::CellRenderer

# register the type (type\_register) and all implemented GLib

inteterfaces  
register\_glib\_type([… optional interfaces …])

…  
end

As I said, not having done much with either GLib/GTK+ in C or Ruby  
extensions, I’m not sure how to actually make this happen, but it seems  
like there ought to be a way to do it since you can already add custom  
signals, properties and register the type. Even if it was via closures  
(which, based on the names used, is how it seems to be implemented in  
Python), it’d still be better than what exists today: if you don’t have  
a signal you can override, you’re SOL.

Surely there’s some way to automatically add these redirects to the  
existing bindings. Unfortunately, I’m not sure where to begin, and I’m  
also under time pressure to get something working with my application.  
I guess this means defining my custom GLib classes in C and then  
wrapping them back to Ruby. ☹

Thanks in advance for any ideas/assistance.

Cheers,

ast

P.S. Some other references (I’m sure you’ve seen most of these already):

## [GObject – 2.0](http://library.gnome.org/devel/gobject/unstable/) [http://live.gnome.org/PyGTK/WhatsNew28](http://live.gnome.org/PyGTK/WhatsNew28) [http://www.sicem.biz/personal/lgs/docs/gobject-python/gobject-tutorial.html](http://www.sicem.biz/personal/lgs/docs/gobject-python/gobject-tutorial.html)

Andrew S. Townley [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
[http://atownley.org](http://atownley.org)

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<div class="post-metadata">

**Author:** ![Andrew\_SSTownley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d07c76/32.png) [@Andrew\_SSTownley](https://www.ruby-forum.com/u/Andrew_SSTownley)\
**Post date:** [September 9, 2008, 3:18pm UTC](https://www.ruby-forum.com/t/extending-gtk-classes-in-ruby-revisited/148108/2 "2008-09-09T15:18:19Z")

</div>

hi,  
i don’t know the answer to your problem, but i’m also interested in the  
solution.  
what kind of renderer would you like to implement?  
do you need something more sophisticated that cannot be accomplished  
with  
[http://ruby-gnome2.sourceforge.jp/hiki.cgi?Gtk%3A%3ACellLayout#set\_cell\_data\_func](http://ruby-gnome2.sourceforge.jp/hiki.cgi?Gtk%3A%3ACellLayout#set_cell_data_func)  
?

regards  
balint

---

<div class="post-metadata">

**Author:** ![Andrew\_SSTownley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d07c76/32.png) [@Andrew\_SSTownley](https://www.ruby-forum.com/u/Andrew_SSTownley)\
**Post date:** [September 9, 2008, 4:24pm UTC](https://www.ruby-forum.com/t/extending-gtk-classes-in-ruby-revisited/148108/3 "2008-09-09T16:24:47Z")

</div>

Hi Balint,

Yep. I need a multi-line text editor embedded in a cell. I found this  
one (done in Python), so I know it’s possible:

[http://www.daa.com.au/pipermail/pygtk/2005-April/009990.html](http://www.daa.com.au/pipermail/pygtk/2005-April/009990.html)

However, it has some issues (other than being in Python). I hacked it  
to make it kinda work, just to see how complete it was. It still has  
some other functionality that would be required in a polished  
application. I’m pretty sure I can do the rest, but I can’t get to the  
get\_size and render methods from Ruby.

I did write a version of an editible table cell (single line) using pure  
Python years ago before the GtkTreeView & friends existed (basically a  
crude version of what’s there today). It took a while to get the  
placement right (along with some guesses in the end), but it did end up  
working quite well. At least this time, the right hooks seem to be  
there, so it should be easier/cleaner to do–provided you can get to  
them from Ruby.

On the upside, I was thinking that I could provide a C + Ruby binding  
for such a critter to the community if I got it working (because I think  
this should be core functionality in GTK+). The current implementation  
doesn’t pay attention to things like yalign during editing if you have a  
long row (I want valign=top), but the default CellEditorText  
implementation always locates the GtkEdit in the middle of the cell  
space. It seems a little half-baked, but I really need something  
equivalent to the type of cell editing support you’d find in Excel or OO  
Calc for what I’m doing (and no, it isn’t another spreadsheet! :)).

I haven’t written any C code in about 7 years, but I did play around  
with trying to port the old asclock applet to the new version of Gnome  
at the time, so I have messed around a little with the GLib/GTK+ type  
system and its approach to OOP. Still, it’s a distraction I  
don’t/didn’t need, but I do need the functionality from a user  
experience point of view.

Thanks for trying to help.

Cheers,

ast

On Tue, 2008-09-09 at 16:17 +0300, Dobai-Pataky Bálint wrote:

> balint
> 
> > According to examples I’ve found, you can do this sort of thing with the  
> > I’m sure that solving this problem would also be very useful to the  
> > implements\_interface(Gtk::foo)
> > 
> > ast  
> > Grand prize is a trip for two to an Open Source event anywhere in the world  
> > [http://moblin-contest.org/redirect.php?banner\_id=100&url=/](http://moblin-contest.org/redirect.php?banner_id=100&url=/)  
> > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ruby-gnome2-devel-en mailing list removed\_email\_address@domain.invalid [ruby-gnome2-devel-en List Signup and Options](https://lists.sourceforge.net/lists/listinfo/ruby-gnome2-devel-en)  
> > –  
> > Andrew S. Townley [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> > [http://atownley.org](http://atownley.org)