calling superclass size_request method

[Kevin Ryde <user42 zip com au>]

With the debian packaged perl-gtk 1.140 and glib 1.161, and gtk 2.12.0
and glib 2.14.1, I had a little go at subclassing a GtkLabel, and in a
"size_request" method calling up to the corresponding superclass code
using signal_chain_from_overridden().  See Foo.pm and main.pl below,
"perl main.pl".

Alas signal_chain_from_overridden doesn't seem to touch the requisition
object, it just stays as size "0x0", where I hoped for something like
"72x17" (which is the case with no signal_request method in the
subclass).  Have I misunderstood something fundamental?  I was sort of
copying what the histogramplot.pl example does, and wanted something
like in C

    GTK_WIDGET_CLASS (my_foo_parent_class)->size_request (widget, requisition);


I suspect actually for what I'm trying to do (tinkering with a clock as
a subclass of GtkLabel) I ought to calculate a desired size on my own,
in advance, instead of asking the superclass and manipulating its
result.  But playing around made me wonder what I was doing wrong
seemingly not to reach the superclass code at all.


package Foo;

use strict;
use warnings;

use Gtk2;
use Glib::Object::Subclass
  Gtk2::Label::,
  signals => { size_request => \&do_size_request };

sub do_size_request ($$) {
  my ($self, $req) = @_;
  print "this is Foo::do_size_request\n";
  print "text is '",$self->get_text,"'\n";
  print "before chain: ",$req->width(),"x",$req->height(),"\n";
  Glib::Object::signal_chain_from_overridden ($self, $req);
  print "after chain: ",$req->width(),"x",$req->height(),"\n";
}

1;

BEGIN { push @INC, '.'; }

use strict;
use warnings;
use Gtk2 '-init';

use Foo;
my $window = Gtk2::Window->new('toplevel');
my $foo = Foo->new();
$foo->set_text ('hello world');
$window->add ($foo);
$window->show_all;

my $req = $foo->size_request();
print "main: size ",$req->width,"x",$req->height,"\n";

Gtk2->main();
exit 0;