=head1 NAME

Gtk2::Buildable - Interface for objects that can be built by Gtk2::Builder

=for position SYNOPSIS

=head1 SYNOPSIS

  package Thing;
  use Gtk2;
  use Glib::Object::Subclass
      Glib::Object::,
      # The important bit -- add this GInterface to our class
      interfaces => [ Gtk2::Buildable:: ],
  
      # Some signals and properties on the object...
      signals => {
          exploderize => {},
      },
      properties => [
          Glib::ParamSpec->int ('force', 'Force',
                                'Explosive force, in megatons',
                                0, 1000000, 5, ['readable', 'writable']),
      ],
      ;
  
  sub exploderize {
      my $self = shift;
      $self->signal_emit ('exploderize');
  }
  
  # We can accept all defaults for Buildable; see the description
  # for details on custom XML.
  
  package main;
  use Gtk2 -init;
  my $builder = Gtk2::Builder->new ();
  $builder->add_from_string ('<interface>
      <object class="Thing" id="thing1">
          <property name="force">50</property>
          <signal name="exploderize" handler="do_explode" />
      </object>
  </interface>');
  $builder->connect_signals ();
  
  my $thing = $builder->get_object ('thing1');
  
  $thing->exploderize ();

  sub do_explode {
      my $thing = shift;
      printf "boom * %d!\n", $thing->get ('force');
  }

  # This program prints "boom * 50!" on stdout.

=cut



=head1 HIERARCHY

  Glib::Interface
  +----Gtk2::Buildable

=for object Gtk2::Buildable - Interface for objects that can be built by Gtk2::Builder
=cut

=head1 DESCRIPTION

In order to allow construction from a Gtk2::Builder UI description
(L<http://library.gnome.org/devel/gtk/unstable/GtkBuilder.html#BUILDER-UI>),
an object must implement the Gtk2::Buildable interface.  The interface
includes methods for setting names and properties of objects, parsing
custom tags, and constructing child objects.

The Gtk2::Buildable interface is implemented by all widgets and many
of the non-widget objects that are provided by GTK+.  The main user of
this interface is Gtk2::Builder, so there should be very little need for
applications to call any of the Gtk2::Buildable methods.

So, instead of focusing on how to call the methods of a Gtk2::Buildable,
this documentation deals with implementing a buildable object.

=head1 WIDGETS

Since Gtk2::Widget implements the Gtk2::Buildable interface, all widgets
get buildability gratis.  If your widget requires no special markup
syntax to express its configuration, and all properties can be handled
through the standard mechanisms, you can simply add the name of your
perl-derived Glib::Object types to the C<object> tag in the builder UI
description.  You don't even have to do anything special in your class
definition.  For example, objects of this class:

  package My::Frame;
  use Gtk2;
  use Glib::Object::Subclass
      Gtk2::Frame::,
      properties => [
          Glib::ParamSpec->int ('foo', ...),
      ],
      ;

  ...

  1;

could be expressed in a builder definition file like this:

  <object class="My__Frame" id="myframe">
    <property name="foo">15</property>
  </object>

Notice that the '::' package separator has been replaced with '__' in the
C<class> attribute; this is because the ':' character is not valid for
GType type names.  The mapping from perl package names to GType names should,
in general, be as simple as transliterating the colons.


=head1 PLAIN OBJECTS

Glib::Object does not implement Gtk2::Buildable by itself, so to get a
builder UI file to create your custom Glib::Object subtypes, you'll have
add the Gtk2::Buildable interface to your class's interfaces list.

  package My::Thing;
  use Gtk2; # to get Gtk2::Buildable
  use Glib::Object::Subclass
      Glib::Object::,
      interfaces => [ 'Gtk2::Buildable' ],
      ...
      ;

Again, if you have no special requirements, then that should be all you need
to do.

=head1 OVERRIDING BUILDABLE INTERFACE METHODS

In some cases, you need to override the default Buildable behavior.  Maybe
your objects already store their names, or you need some special markup
tags to express configuration.  In these cases, add the Gtk2::Buildable
interface to your object declaration, and implement the following methods
as necessary.

=over

=item SET_NAME ($self, $name)

=over

=item * $name (string)

=back

This method should store I<$name> in I<$self> somehow.  For example,
Gtk2::Widget maps this to the Gtk2::Widget's C<name> property.  If you don't
implement this method, the name will be attached in object data down in C
code.  Implement this method if your object has some notion of "name" and
it makes sense to map the XML name attribute to that.

=item string = GET_NAME ($self)

If you implement C<SET_NAME>, you need to implement this method to retrieve
that name.

=item ADD_CHILD ($self, $builder, $child, $type)

=over

=item * $builder (Gtk2::Builder)

=item * $child (Glib::Object or undef)

=item * $type (string)

=back

C<ADD_CHILD> will be called to add I<$child> to I<$self>.  I<$type> can be
used to determine the kind of child.  For example, Gtk2::Container implements
this method to add a child widget to the container, and Gtk2::Notebook uses
I<$type> to distinguish between "page-label" and normal children.  The value
of I<$type> comes directly from the C<type> attribute of the XML C<child> tag.


=item SET_BUILDABLE_PROPERTY ($self, $builder, $name, $value)

=over

=item * $builder (Gtk2::Builder)

=item * $name (string)

=item * $value (scalar)

=back

This will be called to set the object property I<$name> on I<$self>, directly
from the C<property> XML tag.  It is not normally necessary to implement this
method, as the fallback simply calls C<Glib::Object::set()>.  Gtk2::Window
implements this method to delay showing itself (i.e., setting the "visible"
property) until the whole interface is created.  You can also use this to
handle properties that are not wired up through the Glib::Object property
system (though simply creating the property is easier).


=item parser or undef = CUSTOM_TAG_START ($self, $builder, $child, $tagname)

=over

=item * $builder (Gtk2::Builder)

=item * $child (Glib::Object or undef)

=item * $tagname (string)

=back

When Gtk2::Builder encounters an unknown tag while parsing the definition
of I<$self>, it will call C<CUSTOM_TAG_START> to give your code a chance
to do something with it.  If I<$tagname> was encountered inside a C<child>
tag, the corresponding object will be passed in I<$child>; otherwise,
I<$child> will be C<undef>.

Your C<CUSTOM_TAG_START> method should decide whether it supports I<$tagname>.
If not, return C<undef>.  If you do support it, return a blessed perl object
that implements three special methods to be used to parse that tag.  (These
methods are defined by GLib's GMarkupParser, which is a simple SAX-style
setup.)

=over

=item START_ELEMENT ($self, $context, $element_name, $attributes)

=over

=item * $context (Gtk2::Buildable::ParseContext)

=item * $element_name (string)

=item * $attributes (hash reference) Dictionary of all attributes of this tag.

=back


=item TEXT ($self, $context, $text)

=over

=item * $context (Gtk2::Buildable::ParseContext)

=item * $text (string) The text contained in the tag.

=back


=item END_ELEMENT ($self, $context, $element_name)

=over

=item * $context (Gtk2::Buildable::ParseContext)

=item * $element_name (string)

=back

=back

Any blessed perl object that implements these methods is valid as a parser.
(Ain't duck-typing great?)  Gtk2::Builder will hang on to this object until
the parsing is complete, and will pass it to C<CUSTOM_TAG_END> and
C<CUSTOM_FINISHED>, so you shouldn't have to worry about its lifetime.


=item CUSTOM_TAG_END ($self, $builder, $child, $tagname, $parser)

=over

=item * $builder (Gtk2::Builder)

=item * $child (Glib::Object or undef)

=item * $tagname (string)

=item * $parser (some perl object) as returned from C<CUSTOM_TAG_START>

=back

This method will be called (if it exists) when the close tag for I<$tagname>
is encountered.  I<$parser> will be the object you returned from
C<CUSTOM_TAG_START>.  I<$child> is the same object-or-undef as passed to
C<CUSTOM_TAG_START>.


=item CUSTOM_FINISHED ($self, $builder, $child, $tagname, $parser)

=over

=item * $builder (Gtk2::Builder)

=item * $child (Glib::Object or undef)

=item * $tagname (string)

=item * $parser (some perl object) as returned from C<CUSTOM_TAG_START>

=back

This method will be called (if it exists) when the parser finishes dealing
with the custom tag I<$tagname>.  I<$parser> will be the object you returned
from C<CUSTOM_TAG_START>.  I<$child> is the same object-or-undef as passed
to C<CUSTOM_TAG_START>.


=item PARSER_FINISHED ($self, $builder)

=over

=item * $builder (Gtk2::Builder)

=back

If this method exists, it will be invoked when the builder finishes parsing
the description data.  This method is handy if you need to defer any object
initialization until all of the rest of the input is parsed, most likely
because you need to refer to an object that is declared after I<$self> or
you need to perform special cleanup actions.  It is not normally necessary
to implement this method.


=item object or undef = GET_INTERNAL_CHILD ($self, $builder, $childname)

=over

=item * $builder (Gtk2::Builder)

=item * $childname (string)

=back

This will be called to fetch an internal child of I<$self>.  Implement this
method if your buildable has internal children that need to be accessed from
a UI definition.  For example, Gtk2::Dialog implements this to give access
to its internal vbox child.

=back

=cut




=head1 SEE ALSO

L<Gtk2>, L<Glib::Interface>, L<http://library.gnome.org/devel/gtk/unstable/GtkBuilder.html#BUILDER-UI>, L<Gtk2::Buildable::ParseContext>

=head1 COPYRIGHT

Copyright (C) 2003-2008 by the gtk2-perl team.

This software is licensed under the LGPL.  See L<Gtk2> for a full notice.


=cut

