package my_sizer;
use base 'Wx::StaticBoxSizer';
use Wx qw(:sizer);
use Wx::Event qw(EVT_BUTTON);

sub new {
    my $ref = shift;
    my $parent = shift;

    my $self = $ref->SUPER::new(
        Wx::StaticBox->new($parent, -1, 'Box label'),
        wxHORIZONTAL
    );

    my $button = Wx::Button->new($parent, -1, 'Button');
    $self->Add($button);
    EVT_BUTTON($self, $button, \&click);

    $self->SetSizeHints($parent);

    return $self;
}

sub click { Wx::MessageBox('Click!'); }