Mastering Perl/Tk

Radiobutton Values

Groups of Radiobuttons are designed to all use the same -variable option but with unique -value options for each individual Radiobutton. When you select a Radiobutton, any other Radiobuttons assigned the same -variable will be unselected, and that variable will be assigned the -value associated with the selected Button.

You must always use -value when creating Radiobuttons. If you don’t, they won’t select/deselect correctly. There are no defaults for -value.

Here is an example that uses Radiobuttons to control the background color:

# setup the default value we would like
$rb_value = "red";
$mw->configure(-background => $rb_value);

# create the Radiobuttons that will let us change it
foreach (qw(red yellow green blue grey)) {
  $mw->Radiobutton(-text => $_,
                   -value => $_,
                   -variable => \$rb_value,
                   -command => \&set_bg)->pack(-side => 'left');
}

# function to change the background color using $rb_value
sub set_bg {
  print "Background value is now: $rb_value\n";
  $mw->configure(-background => $rb_value);
}

We are storing the status of our Radiobutton group in $rb_value. We set it to an initial value of "red", which happens to match the first Radiobutton we are creating. When any of the Radiobuttons are clicked, including the one currently selected, the subroutine set_bg will be called. This subroutine will print the new value of $rb_value and then change the background of our MainWindow to that color.

If you look at the code closely, you see that we call the configure ...