Exemplo de classe para criar campos personalizados usando a Settings API do WordPress

exemplo_classe_settings_api_wordpress.php

<?php
	if ( ! defined( 'ABSPATH' ) )
		exit; // Exit if accessed directly.
	/**
	 * Pimap Options.
	 *
	 * @package  Pimap/Admin
	 * @category Admin
	 * @author   Leo Baiano <leobaiano@lbideias.com.br>
	 */
	class Options_Meu_Plugin {

		/**
		 * Instance of this class.
		 *
		 * @var object
		 */
		protected static $instance = null;
		/**
		 * Plugin settings.
		 *
		 * @var array
		 */
		public $plugin_settings = array();
		/**
		 * Initialize the plugin
		 */
		public function __construct() {
			// Adds admin menu.
			add_action( 'admin_init', array( $this, 'settings_section_options' ) );
		}

		/**
		 * Creating the options section and fields of plugin options
		 *
		 */
		public function settings_section_options() {
		 	add_settings_section(
				'meu_plugin_section',
				__( 'Opções do plugin', 'meu-plugin' ),
				'__return_false',
				'meu_plugin_options'
			);
		 	add_settings_field(
				'desconto_plus',
				__( 'Desconto Plus', 'meu-plugin' ),
				array( $this, 'text_element_callback' ),
				'meu_plugin_options',
				'meu_plugin_section',
				array(
					'name' => 'meu_plugin_plus',
					'id' => 'meu_plugin_plus',
					'class' => 'input_text',
					'settings' => 'meu_plugin_settings_main'
				)
			);
			// Repete o add_settings_field para criar os outros campos

		 	register_setting( 'meu_plugin_settings', 'meu_plugin_settings_main' );
		}
		/**
		 * Callback to create fields of type text
		 *
		 * @param array $args Data required for the creation of the field
		 * @return string HTML field
		 */
		public function text_element_callback( $args ){
			$name = $args['name'];
			$id = $args['id'];
			$class = $args['class'];
			$settings = $args['settings'];
			$valueArr = get_option( $settings, array() );
			if( isset( $valueArr[$name] ) )
				$value = $valueArr[$name];
			else
				$value = '';
			echo sprintf( '<input type="text" id="%2$s" name="%4$s[%1$s]" value="%5$s" class="%3$s" />', $name, $id, $class, $settings, $value ) . ' % ';
		}
	}