I'm not sure what you want to see, so below is the code for the whole subroutine I'm writing

The whole reason I have this subroutine is for user to select some items in the @newSeqUnique array and return the selected array to the calling function

Currently the code is stuck at the MainLoop; statement

 
sub getSelectedSeq {
    my $newSeqUniqueRef = shift; my $grp = shift;
    my @newSeqUnique = @$newSeqUniqueRef;
    my @newSeqUniqueSorted = sort{$a->{ID} cmp $b->{ID} ||
                    $a->{folder} cmp $b->{folder}} @newSeqUnique;
    my @displayedArr; my $displayedStr;
    my @selectedArr;
    foreach (@newSeqUniqueSorted) {
        $displayedStr = $_->{ID}." - ".$_->{folder};
        push (@displayedArr, $displayedStr);
    }
    select STDOUT;
    foreach (@displayedArr) {
        print "$_\n";
    }

#    my $mw = MainWindow->new(-title=>"Select sequences");
    my $mw = new MainWindow;
    
    $mw->Label(-text => "Below is a list of sequences not found in exi
+sting group $grp table")->pack();
    $mw->Label(-text => "Please select sequences to be added to new ta
+ble")->pack();
    
    my $lb = $mw->Scrolled("Listbox",
               -scrollbars => "osoe",
               -height =>10,
               -width => 30,
               -selectmode => "extended");

        my $real_lb = $lb->Subwidget('scrolled');
        $real_lb->configure(-borderwidth=>2);
    $lb->insert("end", @displayedArr);
    $lb->pack(-fill=>"both");
    $mw->Button(-text => "Select",
                     -command => sub{@selectedArr=$lb->curselection;$m
+w->destroy();})->pack();
    $lb->selectionSet('end');
    $lb->see('end');
    MainLoop();

    foreach (@selectedArr) {
                print "$_\n";
        }
        
    my @arr; my @temp; my ($index, $ID, $folder, $obj);
    if ((@selectedArr)&&(defined $selectedArr[0])) {
        foreach (@selectedArr) {
            push (@arr, $newSeqUniqueSorted[$_]);
        }
    }else {
        @arr = ();
    }
    
    return \@arr;
}
[download]

I can't replicate your problem. I added use Tk; to the top of the script, and the following to the bottom:

print %{ getSelectedSeq([{ ID     => 1,
                           folder => '/'
                         },
                         { ID     => 2,
                           folder => 'home'
                         }], 12)->[0] };
[download]

I'm getting the output and the program terminates.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

I have spent more than 1 day on this bug and I have completely no idea why I have this problem. In my program there are also other subroutines which display popup windows but none of them have this problem. I notice that to display other pop-ups I used $main->Show;, probably that's why I never encountered this problem?

Is there any other way of displaying this selection box without having to write MainLoop; at all? So far I have tried 2 ways as shown in the code but they all hang. I'm using Perl 5.8.4 and I can't install any additional library.

When I try Tk::exit;, the whole program terminates, not just the GUI :(((

Can you enlighten me on how I can use dialog box to do the same purpose? :P

I wanted to use dialog to do this, but could not find any code example on how :(. If can do this with dialog box it would be great!