Subclassing Gtk2::CellRenderer

[Bjarne Steinsbø <bosteins broadpark no>]

Background: I want to create a custom cell renderer for TreeView to 
allow cells to be editable by using something that might look like an 
OptionMenu or a Combo.

Since I'm new to Gtk, I (try to) start off by doing nothing, i.e. 
implement my own renderer that inherits everything from an existing 
renderer.  The point is to get to grips with the basics of GObject 
inheritance etc.

So, I made a few small changes to the (1.0rc3) example "simplelist.pl" 
(please see attached diff), and implemented a basically empty class 
(please see attached "MyRenderer.pm").  So far so good.  The printf's 
seem to indicate that stuff is routed through my class and since the 
example still works, it looks as if I'm on the correct track.

Next step is to try to override a method, and just delegate the handling 
to the parent class.  The Gtk documentation shows that a 
"GtkCellRenderer" class (the superclass of "GtkCellRendererText", which 
again is the class that "MyRenderer" inherits from) should have a 
"gtk_cell_renderer_render" method, called whenever the cell needs to be 
rendered.  Looks good as a test case,  this method will obviously be the 
crux of the matter when going back to what I eventually would like to do.

A method invocation in GObject is just a signal, right?  So I should 
override the proper signal name in order to let my own routine handle 
this method.

However, when I try to install an overridden method (uncommenting line 7 
in "MyRenderer.pm") the way I think method overriding is to be done, I 
get an error message saying "can't override class closure for unknown 
signal render at ...".  Where am I going wrong?

Bjarne

*** /usr/src/Gtk2-perl/Gtk2-1.00rc3/examples/simplelist.pl      Fri Sep 26 01:26:33 2003
--- simplelist.pl       Wed Oct  1 15:03:23 2003
***************
*** 29,30 ****
--- 29,32 ----
  
+ use MyRenderer;
+ 
  # add a new type of column that reverses the text that's in a scalar
***************
*** 33,35 ****
                type     => 'Glib::Scalar',      
!               renderer => 'Gtk2::CellRendererText',   
                attr     => sub {
--- 35,37 ----
                type     => 'Glib::Scalar',      
!               renderer => 'MyRenderer',   
                attr     => sub {
***************
*** 84,85 ****
--- 86,91 ----
  $scwin->add ($slist);
+ printf STDERR "Renderer for column 5 is %s\n",
+     $slist->get_column (5)->get_cell_renderers;
+ printf STDERR "Renderer for column 6 is %s\n",
+     $slist->get_column (6)->get_cell_renderers;
  

package Gtk2::CellRendererText::MyRenderer;
use strict;
use Gtk2;

use Glib::Object::Subclass Gtk2::CellRendererText::,
    signals => {
        render => \&do_render,
#       get_size => \&do_get_size,
    },
    properties => [ ],
;

# Overridden render
sub do_render {
    my $self = shift;
    print STDERR "MyRenderer::render called\n";
    $self->signal_chain_from_overridden;
}

sub do_get_size {
    my $self = shift;
    print STDERR "MyRenderer::get_size called\n";
    $self->signal_chain_from_overridden;
}

sub INIT_INSTANCE {
    my $self = shift;
    print STDERR "MyRenderer::INIT_INSTANCE called\n";
    printf STDERR "Type of self = %s\n", $self;
}

1;