in reply to Tk Optionmenu - how to set the default selection

Here is one way, manipulate the options array. 
#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my @hrs = ("1", "2", "3", "4", "5", "6",
"7", "8", "9", "10", "11", "12");

my $mw = new MainWindow();
my $menu = $mw->Optionmenu( 
           -options => \@hrs,  
       -textvariable => \$hrs[0] )->pack();

$mw->Button(-text=>'Shift',-command => sub{
      push (@hrs, shift(@hrs));
      $menu->configure(-options => \@hrs, -textvariable => \$hrs[0] );
      $mw->update;
    })->pack();

#start up at desired value
my $desired = 3;
push (@hrs, shift(@hrs)) until $hrs[0] == 3;
$menu->configure(-options => \@hrs, -textvariable => \$hrs[0] );

MainLoop;

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Re^2: Tk Optionmenu - how to set the default selection
by Minok (Novice) on Feb 10, 2009 at 18:29 UTC
    Well, there-in lies the solution. Just setting the attribute of -textvariable a second time fixed the issue.

    Adding 

    $platformDropdown -> configure( -textvariable => \$platformChoice );

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    to the end does the trick.... which pokes the TK engine and says "Hey, set the value to THIS". Even though the variable already contained the right value, I guess TK needs to have some sort of event to know it needs to update. So the corrected code, that now works, looks like: 
    my %solutionMatrix;    
my $defaultPlatform = "Mod1";
$solutionMatrix{"Mod1"} = [ 'a','b','c' ];
$solutionMatrix{"Mod2"} = [ 'q' ]; 

    my $platformDropdown = $selectionFrame -> Optionmenu ( -textvariab
+le => \$platformChoice, -indicatoron => 1 ) -> pack( -side => "left")
+;

        # --- now populate the options in the platform and customer dr
+opdown list,  
        #  which is in the hash of arrays, %solutionMatrix
        foreach my $platform ( sort keys %solutionMatrix ) {
            # $platform is a choice for the platform dropdown
            # @{$solutionMatrix{$platform} is an array of solutions fo
+r the customer dropdown
            $platformDropdown -> addOptions([$platform=>$platform]);
        }

        $platformChoice = $defaultPlatform;    # set default
        $platformDropdown -> configure( -textvariable => \$platformCho
+ice );

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