Cacher is the code snippet organizer for pro developers

<?php
/**
 * Classe para criar Metaboxes mais manuteníveis no Wordpress.
 * 
 * PHP versions 5.3+
 */
class Metabox
{
    public function __construct($key, $title, $screen, $callback=null)
    {
        $this->key = $key;
        $this->title = $title;
        $this->screen = $screen;
        $this->callback_function = $callback;

        add_action('add_meta_boxes', array($this, 'metabox'));
        add_action('save_post', array($this, 'save_metabox'));
    }

    public function metabox()
    {
        add_meta_box($this->key, $this->title, array($this, 'build_metabox'), $this->screen);
    }

    public function build_metabox($post)
    {
        $meta_val = get_post_meta($post->ID, $this->key);
        call_user_func_array($this->callback_function, array($post, $this->key, $meta_val));
    }

    public function save_metabox($post_id)
    {
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
        update_post_meta($post_id, $this->key, $_POST[$this->key]);
    }
};

/* Metabox de teste */
new Metabox(
	'titulo',
	'Título da minha Metabox',
	null,
	function($post, $meta_key, $meta_val) {
		echo '<input type="text" value="'.esc_attr($meta_val[0]).'" name="'.$meta_key.'" />';
	}
);