Displaying new custom option in WooCommerce

display-special-field-woocommerce.php

<?php

class WC_Settings_Hola_Dolly extends WC_Settings_Page {

  public function __construct() {
    $this->id    = 'hola-dolly';
    $this->label = __( 'Hola Dolly', 'hola-dolly' );

    // Añadir pestaña
    add_filter( 'woocommerce_settings_tabs_array', array( $this, 'add_settings_page' ), 20 );

    // Mostrar los campos
    add_action( 'woocommerce_settings_' . $this->id, array( $this, 'output' ) );

    // Guardar los cambios
    add_action( 'woocommerce_settings_save_' . $this->id, array( $this, 'save' ) );

    // Muestra nuestro campo especial
    add_action( 'woocommerce_admin_field_holadolly_special_field', array( &$this, 'display_special_field' ) );

  }

  public function display_special_field( $field ) {
    var_dump( $field );
  }

  public function get_settings() {

    $settings = array(

      array( 'title' => __( 'Opciones Generales', 'hola-dolly' ), 'type' => 'title', 'id' => 'holadolly_general_options', 'desc' => __( 'Nuestras opciones generales.', 'hola-dolly' ) ),
      array(
        'title'     => __( 'Un número', 'hola-dolly' ),
        'id'       => 'holadolly_general_options_number',
        'default'    => 0,
        'type'       => 'number',
        'desc_tip'    => __( 'Pon un número por aquí', 'hola-dolly' )
      ),
      array( 'type' => 'sectionend', 'id' => 'holadolly_general_options' ),

      array( 'title' => __( 'Opciones Especiales', 'hola-dolly' ), 'type' => 'title', 'id' => 'holadolly_special_options', 'desc' => __( 'Nuestras opciones especiales.', 'hola-dolly' ) ),
      // Aquí va nuestro campo especial encerrado en una nueva sección
      array( 
        'title'     => __( 'Campo especial', 'hola-dolly' ),
        'id'     => 'holadolly_general_options_special',
        'default'  => '',
        'type'     => 'holadolly_special_field'
      ),
      array( 'type' => 'sectionend', 'id' => 'holadolly_special_options' ),




    );

    return apply_filters( 'holadolly_woocommerce_holadolly_settings', $settings );
  }

}

new WC_Settings_Hola_Dolly();