Wordpress API Settings

<?php
    class Liv_Theme_Settings{

        var $options;

        public function __construct(){
            $this->options  = get_option('liv_settings');
        }

        public function menu_option() {
            add_options_page( "Liv Settings", "Liv Settings", 'manage_options', __FILE__, array($this, 'show_settings') );
            //add_menu_page( "Liv Settings", "Liv Settings", 'manage_options', __FILE__, array($this, 'show_settings'), '', 100 );
        }

        public function show_settings(){?>
            <div id="theme-options-wrap">
            <div class="icon32" id="icon-tools">
            </div>
            <h2 style="padding-top:15px;">Configuración</h2>
            <form method="post" action="options.php" enctype="multipart/form-data">
            <?php

            settings_fields('liv_settings');

            do_settings_sections(__FILE__);

            ?>
            <p class="submit"><input name="Submit" type="submit"
                class="button-primary" value="<?php esc_attr_e('Save Changes'); ?>" />
            </p>
            </form>
            </div>
            <?php
        }

        public function register_and_create_fields(){
            register_setting('liv_settings', 'liv_settings', array($this, 'validate_setting'));

            add_settings_section('general_settings', '', array($this, 'show_general_settings_section'), __FILE__);

            add_settings_field('contact_mail', 'Mail de contacto:', array($this, 'show_contact_mail'), __FILE__, 'general_settings');
        }

        function show_contact_mail(){
            echo "<input class='settings_input_field' name='liv_settings[contact_mail]' id='contact_mail' type='text' value='".$this->get_option('contact_mail')."' />";
        }


        function show_general_settings_section(){
        }


        public function validate_setting($plugin_options){
            return $plugin_options;
        }

        function get_option($field_id){
            return @$this->options[$field_id];
        }

    }

    global $liv_settings;

    $liv_settings   = new Liv_Theme_Settings();

    add_action( 'admin_menu', array($liv_settings, 'menu_option' ));
    add_action('admin_init', array($liv_settings, 'register_and_create_fields'));
?>