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# $Id: composite.pod 1.2 Wed, 12 Nov 1997 00:30:45 +0100 ach $
=head1 NAME
Tk::composite - Defining a new composite widget class
=for category Derived Widgets
=head1 SYNOPSIS
package Tk::MyNewWidget;
use Tk::widgets qw/ list of Tk widgets /;
use base qw/ Tk::Frame /; # or Tk::Toplevel
Construct Tk::Widget 'MyNewWidget';
sub ClassInit {
my( $class, $mw ) = @_;
#... e.g., class bindings here ...
$class->SUPER::ClassInit( $mw );
}
sub Populate {
my( $self, $args ) = @_;
my $flag = delete $args->{-flag};
if( defined $flag ) {
# handle -flag => xxx which can only be done at create
# time the delete above ensures that new() does not try
# and do $self->configure( -flag => xxx );
}
$self->SUPER::Populate( $args );
$self = $self->Component( ... );
$self->Delegates( ... );
$self->ConfigSpecs(
'-cursor' => [ SELF, 'cursor', 'Cursor', undef ],
'-something' => [ METHOD, dbName, dbClass, default ],
'-text' => [ $label, dbName, dbClass, default ],
'-heading' => [ {-text => $head},
heading, Heading, 'My Heading' ],
);
}
sub something {
my( $self, $value) = @_;
if ( @_ > 1 ) {
# set it
}
return # current value
}
1;
__END__
=head1 NAME
Tk::Whatever - a whatever widget
=head1 SYNOPSIS
use Tk::Whatever;
$widget = $parent->Whatever(...);
=head1 DESCRIPTION
...
=head1 DESCRIPTION
The intention behind a composite is to create a higher-level widget,
sometimes called a "super-widget" or "mega-widget". Most often,
a composite will be
built upon other widgets by B<using> them, as opposed to specializing on them.
For example, the supplied composite widget B<LabEntry> is I<made of> an
B<Entry> and a B<Label>; it is neither a I<kind-of> B<Label>
nor is it a I<kind-of> B<Entry>.
Most of the work of a composite widget consistd in creating subwidgets,
arranging to dispatch configure options to the proper subwidgets and manage
composite-specific configure options.
=head1 GLORY DETAILS
Depending on your Perl/Tk knowledge this section may be enlighting
or confusing.
=head2 Composite Widget
Since Perl/Tk is heavilly using an object-oriented approach, it is no
suprise that creating a composite goes through a B<new()> method.
However, the composite does not normally define a B<new()> method
itself: it is usually sufficient to simply inherit it from
B<Tk::Widget>.
This is what happens when the composite uses
use base qw/ Tk::Frame /; # or Tk::Toplevel
to specify its inheritance chain. To complete the initialisation of the
widget, it must call the B<Construct> method from class B<Widget>. That
method accepts the name of the new class to create, i.e. the package name
of your composite widget:
Construct Tk::Widget 'MyNewWidget';
Here, B<MyNewWidget> is the package name (aka the widget's B<class>). This
will define a constructor method for B<MyNewWidget>, normally named after the
widget's class. Instanciating that composite in client code would
the look like:
$mw = MainWindow->new; # creates a top-level MainWindow
$self = $mw->MyNewWidget(); # creates an instance of the
# composite widget MyNewWidget
Whenever a composite is instanciated in client code,
C<Tk::Widget::new()> will be invoked via the widget's class
constructor. That B<new> method will call
$self->Populate(\%args);
where I<%args> is the arguments passed to the widget's constructor. Note
that B<Populate> receives a B<reference> to the hash array
containing all arguments.
B<Populate> is typically defined in the composite class (package),
which creates the characteristic subwidgets of the class.
=head2 Creating Subwidgets
Subwidget creation happens usually in B<Populate()>.
The composite usually calls the
subwidget's constructor method either directly, for "private" subwidgets,
or indirectly through the B<Component> method for subwidgets that should
be advertised to clients.
B<Populate> may call B<Delegates> to direct calls to methods
of chosen subwidgets. For simple composites, typically most if not all
methods are directed
to a single subwidget - e.g. B<ScrListbox> directs all methods to the core
B<Listbox> so that I<$composite>-E<gt>B<get>(...) calls
I<$listbox>-E<gt>B<get>(...).
=head2 Defining mega-widget options
B<Populate> should also call B<ConfigSpecs()> to specify the
way that configure-like options should be handled in the composite.
Once B<Populate> returns, method B<Tk::Frame::ConfigDefault>
walks through the B<ConfigSpecs> entries and populates
%$args hash with defaults for options from X resources (F<.Xdefaults>, etc).
When B<Populate> returns to B<Tk::Widget::new()>,
a call to B<$self>-E<gt>I<configure>(%$args) is made which sets *all*
the options.
=head1 SEE ALSO
L<Tk::ConfigSpecs|Tk::ConfigSpecs>
L<Tk::mega|Tk::mega>
L<Tk::Derived|Tk::Derived>
=cut
|
