The code you posted runs fine here, so I don't know what your problem is. The following shows how to do row selection.

#!/usr/bin/perl -w
use Data::Dumper;
use Gtk2 -init;
use Gtk2::Ex::Simple::List;

my $win = Gtk2::Window->new;
$win->set_title ('Gtk2::Ex::Simple::List exapmle');
$win->set_border_width (6);
$win->set_default_size (500, 300);
$win->signal_connect (delete_event => sub { Gtk2->main_quit; });

my $hbox = Gtk2::HBox->new (0, 6);
$win->add ($hbox);

my $scwin = Gtk2::ScrolledWindow->new;
$hbox->pack_start ($scwin, 1, 1, 0);
$scwin->set_policy (qw/automatic automatic/);

my $slist = Gtk2::Ex::Simple::List->new (
    'Name'          => 'text',
);

$slist->get_selection->set_mode ('multiple');

@{$slist->{data}} = ('a'..'z');



$scwin->add ($slist);

my $vbox = Gtk2::VBox->new (0, 6);
$hbox->pack_start($vbox, 0, 1, 0);

my $button = Gtk2::Button -> new('What\'s Selected by indices?');
$button -> signal_connect(clicked => \&report_indices, $window);
# pack quit button into $main_vbox
$vbox -> pack_start($button, 0, 1, 0);

my $button1 = Gtk2::Button -> new('What\'s Selected by value?');
$button1 -> signal_connect(clicked => \&report_items, $window);
# pack quit button into $main_vbox
$vbox -> pack_start($button1, 0, 1, 0);

my $button2 = Gtk2::Button -> new('Delete a value(s)');
$button2 -> signal_connect(clicked => \&del_items, $window);
# pack quit button into $main_vbox
$vbox -> pack_start($button2, 0, 1, 0);

my $button3 = Gtk2::Button -> new('Insert values at pos 2');
$button3 -> signal_connect(clicked => \&add_items, $window);
# pack quit button into $main_vbox
$vbox -> pack_start($button3, 0, 1, 0);

my $button4 = Gtk2::Button -> new('Overwrite values at pos 2');
$button4 -> signal_connect(clicked => \&rpl_items, $window);
# pack quit button into $main_vbox
$vbox -> pack_start($button4, 0, 1, 0);


# finally, a button to end it all
$btn = Gtk2::Button->new_from_stock ('gtk-quit');
$btn->signal_connect (clicked => sub  { Gtk2->main_quit; });
$vbox->pack_end($btn, 0, 1, 0);

$win->show_all;
Gtk2->main;

sub del_items {
 my @indices = $slist -> get_selected_indices;
    
  #need to sort numerically, and splice off the highest numbers first 
+   
  foreach my $i (reverse sort {$a<=>$b} @indices ) {
           print "$i\n";
           splice @{ $slist->{data} }, $i, 1;     
    }        
}

sub add_items {
       my @new;
       for(1..5){push @new,int rand 100}
       # adds 5 elements at pos 2, shifting others over               
+       
       splice @{ $slist->{data} }, 2, 0, @new;
}

sub rpl_items {
       my @new;
       for(1..5){push @new,int rand 100}
       
       # adds 5 elements at pos 2, removing previous items            
+          
       splice @{ $slist->{data} }, 2, 5, @new;
}

sub report_indices {
    my @indices = $slist -> get_selected_indices;
    
    foreach my $i (@indices) {
        print $i . "\n"; # I'd rather print the actual data here.
    }        
}

sub report_items {
    my @indices = $slist -> get_selected_indices;
    
    foreach my $i (@indices) {
        print $slist->{data}[$i][0] . ' '; 
    }        

   print "\n";
}
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