(after MainLoop has been called)

Not after the MainLoop. This loop never exits (if you don't destroy the MainWindow, that is).

Instead, you bind events to code (subroutines), which does what you want (e.g. create widgets). Then if a event is triggered, the code bound to this event is executed.

populate a grid managed frame

You just create those widgets as children of the frame:

$Frame->$Widget(@args);
[download]

where $Widget is Button, Frame, Entry, Canvas, ... etc.

It's been a while since TK for me..but i do remember that had to re-pack parent container under certain circumstances to get widgets to update.
the hardest line to type correctly is: stty erase ^H

#!/usr/bin/perl
use strict;
use Tk;
use Tk::HList;

my $mw = MainWindow->new();

$mw->geometry("500x500+100+100");

my $h;

#create some sample data
my %data;

foreach (0..100) {
      $data{$_}{'name'} = 'name'.$_;
      $data{$_}{'id'} =   rand(time);
     }
#get random list of keys
my @keys = keys %data; 

#################


my $button0 = $mw->Button(-text => 'show list',
                         -command => sub{ showlist() } )->pack;


my $button = $mw->Button(-text => 'exit',
                         -command => sub{exit})->pack;

my $sortid = $mw->Button(-text => 'Sort by Id',
                         -command => [\&sort_me,1] )->pack;


MainLoop;
#########################################################


sub showlist{

$h = $mw->Scrolled( 'HList', 
                       -header => 1,
                       -columns => 2,
                       -width => 30,
                       -height => 60,
                       -takefocus => 1,
                       -background => 'steelblue',
                   -foreground =>'snow',
               -selectmode => 'single',
                       -selectforeground => 'pink',
                       -selectbackground => 'black',
                #       -browsecmd => \&browseThis,
                   )->pack(-side => "left", -anchor => "n");

my $nameh = $h->header('create', 0, -text => '   Name  ',
                        -borderwidth => 3,
                        -headerbackground => 'steelblue',
            -relief => 'raised');

my $idh = $h->header('create', 1, -text => '      ID      ',
                        -borderwidth => 3,
                        -headerbackground => 'lightsteelblue',
                    -relief => 'raised');


foreach (@keys) {
     my $e = $h->addchild(""); #will add at end
        
     $h->itemCreate ($e, 0,
           -itemtype => 'text',
           -text => $data{$_}{'name'},
            );
                        
     $h->itemCreate($e, 1,
           -itemtype => 'text',
           -text => $data{$_}{'id'},
         );

}

}




sub sort_me{
  my $col = shift;

  my @entries = $h->info('children');
  my @to_be_sorted =();

 foreach my $entry(@entries){
           push @to_be_sorted,
       [ $h->itemCget($entry,0,'text'),
         $h->itemCget($entry,1,'text')
       ];
           }

  my @sorted = sort{ $a->[$col] cmp $b->[$col] } @to_be_sorted;
            
my $entry = 0;
  foreach my $aref (@sorted){
#    print $aref->[0],' ',$aref->[1],"\n";
    $h->itemConfigure( $entry, 0, 'text' => $aref->[0] );  
    $h->itemConfigure( $entry, 1, 'text' => $aref->[1] ); 
    $entry++;
  }

$mw->update;
}
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I looked at HList but it wasn't clear that I could easily create a scrolling grid of thumbnails with it. I want a rectangular area with rows and columns of thumbnails that I can select and operate on. (Ultimately I'd like to be able to remove thumbnails as operations are completed but that's for later.)

You can use Hlist for thumbnails, see ztkdb and ztkdb-sql

HList is the most configurable list in Tk.

You can also use Gtk2's various list widgets, which accept pixbuf fields.

---

I'm not really a human, but I play one on earth.
Old Perl Programmer Haiku

In my callback I have a call to this subroutine:

sub ThumbNail {
    my($name) = @_;

    my $row = $img_id % 4;
    my $col = $img_id - 4 * $row;
    my $img = $frame->Photo(-format => 'jpeg', -file => $name);
    my $iratio = $img->width()/200;
    my $nh = $img->height()/$iratio;
    my $newimg = $frame->Photo(-width => 200, -height => $nh);
    $newimg->copy($img, -subsample=>($iratio, $iratio));
    my $imgL = $frame->Label('-image' => $newimg)->pack;
    $imgL->bind('<Button-1>', [\&doFocus, $imgL] );
    $imgL->bind ( '<Key-1>' ,  [\&rate, $img_id, 1]);
    $imgL->bind ( '<Key-2>' ,  [\&rate, $img_id, 2]);
    $imgL->bind ( '<Key-3>' ,  [\&rate, $img_id, 3]);
    $imgL->bind ( '<Key-4>' ,  [\&rate, $img_id, 4]);
    $imgL->bind ( '<Key-5>' ,  [\&rate, $img_id, 5]);
    @imgs[$img_id] = { name => $name, lbl => $imgL, sel => 0 };
    $img_id++;
    return $imgL;
    
}
[download]

Some command windows flicker and then it aborts.