perltk-toolkit

Why is changing the class of a widget in perl tk wrecking the widget

Simplified code to show the problem:

my $mw = MainWindow->new;

my $label = $mw->Label(-text => 'Hello', -class => 'Class1')->pack;
$label->configure(-class => 'Class2');

MainLoop;

.Xresources file:

classfunny*Class1.foreground: green
classfunny*Class2.foreground: red

Without the configure statement the program runs as expected. With the statement the label shrinks to almost nothing and shows nothing. On buttons the button text vanishes after the configure. Changing text with configure works fine, so why is changing the class causing a problem.

Solution

  • The class of a widget can't be changed. There is no configure option -class for Tk widgets after creation.

    See Tk::options documentation

    Unfortunately your attempt to configure -class does not throw an error, which is a bug. If you add another config option to the configure call like so:

     $label->configure(-bg=>'white',-class=>'Class2');

    Tk warns unknown option "-class" at test.pl line 9.