Currently, Perl/Tk generates a
<<MenuSelect>> virtual event whenever
a menu is posted and the active menu item changes.[28] This code binds a callback that
prints on STDOUT the -label option of the active
menu item. The special variable $Tk::event is a
localized reference to the X11 event structure (the same thing
returned by a call to XEvent, described in Chapter 15, "Anatomy of the MainLoop"). Its W method returns the
widget reference that the event occurred in, which is the Menu in
this case. The use of Tk::catch isn't
strictly necessary but does prevent the code from exiting if
$menu isn't a Menu reference.
Tk::Catch is essentially a block eval designed to
trap and ignore exceptions.
[28] On
Unix, multiple events are generated as the cursor moves over the
menu. On Win32, a single event is generated whenever the active menu
item changes.
$menu->bind('<<MenuSelect>>' => sub {
my $label = undef;
my $menu = $Tk::event->W;
Tk::catch {$label = $menu->entrycget('active', -label)};
print "palette=$palette, menu label=$label!\n" if defined $label;
});
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