Calling php classes from other files

Question

I am working on some custom post types. I finished the first one and realized that the metabox code I was using could be re-used by other, future, custom post types (as well as pages, posts, etc). So I put the class in its own php file and included it from the functions.php file of my child theme. I've never used classes before, but I thought I could then call that class from wherever I wanted since that is what I do for functions. instead I called it from my post-types.php file and got the following error:

"Fatal error: Class 'My_meta_box' not found in D:\helga\xampp\htdocs\plagueround\wp-content\themes\plagueround_new2\functions\post-types.php on line 73"

In the functions.php of my child theme I've included the file where my class lives:

define('CHILDTHEME_DIRECTORY', get_stylesheet_directory() . '/');
// Meta Box Class - makes meta boxes
require_once(CHILDTHEME_DIRECTORY . 'functions/meta_box_class.php');

here's my class

//My Meta Box CLASS
//from: http://www.deluxeblogtips.com/2010/05/howto-meta-box-wordpress.html

class My_meta_box {

        protected $_meta_box;

        // create meta box based on given data
        function __construct($meta_box) {
        $this->_meta_box = $meta_box;
        add_action('admin_menu', array(&$this, 'add'));

        add_action('save_post', array(&$this, 'save'));
    }

    /// Add meta box for multiple post types
    function add() {
        foreach ($this->_meta_box['pages'] as $page) {
            add_meta_box($this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']);
        }
    }

    // Callback function to show fields in meta box
    function show() {
        global $post;

        // Use nonce for verification
        echo '<input type="hidden" name="mytheme_meta_box_nonce" value="', wp_create_nonce(basename(__FILE__)), '" />';

        echo '<table class="form-table">';

        foreach ($this->_meta_box['fields'] as $field) {
            // get current post meta data
            $meta = get_post_meta($post->ID, $field['id'], true);

            echo '<tr>',
                    '<th style="width:20%"><label for="', $field['id'], '">', $field['name'], '</label></th>',
                    '<td>';
            switch ($field['type']) {
                case 'text':
                    echo '<input type="text" name="', $field['id'], '" id="', $field['id'], '" value="', $meta ? $meta : $field['std'], '" size="30" style="width:97%" />',
                        '<br />', $field['desc'];
                    break;
                case 'textarea':
                    echo '<textarea name="', $field['id'], '" id="', $field['id'], '" cols="60" rows="4" style="width:97%">', $meta ? $meta : $field['std'], '</textarea>',
                        '<br />', $field['desc'];
                    break;
                case 'select':
                    echo '<select name="', $field['id'], '" id="', $field['id'], '">';
                    foreach ($field['options'] as $option) {
                        echo '<option', $meta == $option ? ' selected="selected"' : '', '>', $option, '</option>';
                    }
                    echo '</select>';
                break;
                case 'select2': //for when value and display text don't match
                                //$options array must be multidimensional with both the 'value' and the 'text' for each option
                                //for example = array( array(text=>text1,value=>value1),array(text=>text2,value=>value2))
                                //then in <option> value = $option['value'] and text = $option['text']
                    echo '<select name="', $field['id'], '" id="', $field['id'], '">';
                    foreach ($field['options'] as $option) {
                        echo '<option value="',$option['value'],'"', $meta == $option['value'] ? ' selected="selected"' : '', '>', $option['desc'], '</option>';
                    }
                    echo '</select>';
                    break;
                case 'radio':
                    foreach ($field['options'] as $option) {
                        echo '<input type="radio" name="', $field['id'], '" value="', $option['value'], '"', $meta == $option['value'] ? ' checked="checked"' : '', ' />', $option['name'];
                    }
                    break;
                case 'checkbox':
                    echo '<input type="checkbox" name="', $field['id'], '" id="', $field['id'], '"', $meta ? ' checked="checked"' : '', ' />';
                    break;
            }
            echo    '<td>',
                '</tr>';
        }

        echo '</table>';
    }

    // Save data from meta box
    function save($post_id) {
        // verify nonce
        if (!wp_verify_nonce($_POST['mytheme_meta_box_nonce'], basename(__FILE__))) {
            return $post_id;
        }

        // check autosave
        if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
            return $post_id;
        }

        // check permissions
        if ('page' == $_POST['post_type']) {
            if (!current_user_can('edit_page', $post_id)) {
                return $post_id;
            }
        } elseif (!current_user_can('edit_post', $post_id)) {
            return $post_id;
        }

        foreach ($this->_meta_box['fields'] as $field) {
            $old = get_post_meta($post_id, $field['id'], true);
            $new = $_POST[$field['id']];

            if ($new && $new != $old) {
                update_post_meta($post_id, $field['id'], $new);
            } elseif ('' == $new && $old) {
                delete_post_meta($post_id, $field['id'], $old);
            }
        }
    }
}

then in my post-types.php file where i am defining some meta boxes for a custom post type i have:

$prefix = '_events_';
$post_id = $_GET['post'] ? $_GET['post'] : $_POST['post_ID'] ;

$events_meta_box = array(
    'id' => 'wpt_events',
    'title' => 'Events Options',
    'pages' => array('events'), // multiple post types possible
    'context' => 'side',
    'priority' => 'low',
    'fields' => array(
        array(
            'name' => 'Headline',
            'desc' => 'Enter the heading you\'d like to appear before the video',
            'id' => $prefix . 'heading1',
            'type' => 'text',
            'std' => ''
        ),

    )

);

$my_box = new My_meta_box($events_meta_box); 

So- how do I reference classes from other files?

EDITS/CONTINUATION

simply moving the require_once statement to the post-types.php (the one trying to call the class) seemed to work. but for the heck of it i tried the autoload script

function __autoload($className)
{
        require(CHILDTHEME_DIRECTORY .'functions/class_' . $className . '.php')  ;
}

where I renamed my class file to class_My_meta_box.php and My_meta_box is the class name

which results in the following errors: Warning: require(D:\helga\xampp\htdocs\plagueround/wp-content/themes/plagueround_new/functions/class_WP_User_Search.php) [function.require]: failed to open stream: No such file or directory in D:\helga\xampp\htdocs\plagueround\wp-content\themes\plagueround_new\functions.php on line 66

Fatal error: require() [function.require]: Failed opening required 'D:\helga\xampp\htdocs\plagueround/wp-content/themes/plagueround_new/functions/class_WP_User_Search.php' (include_path='.;D:\helga\xampp\php\PEAR') in D:\helga\xampp\htdocs\plagueround\wp-content\themes\plagueround_new\functions.php on line 66

i don't totally understand what it says, BUT i think it is trying to autoload some default wordpress class... and is looking in my directory where it obviously doesn't exist.

Answer 1

Just use the absolute path:

require_once("fullpath/functions/meta_box_class.php") or die ("Could Not load file");

Answer 2

Actually, it doesnt matter if the file contains a class or something else. For PHP being able to execute code from other files, PHP has to know where the file is, so it's your regular require or include.

Example:

// foo.class.php
class Foo {}

// main.php
require_once '/path/to/foo.class.php';
$foo = new Foo;

When using classes, it actually makes sense to use a Naming Convention and use an Autoloader, so PHP will try to include the class on it's own, without you having to require or include it.

Answer 3

It looks like meta_box_class.php isn't being included. To find out what files have been included at any point, try:

var_dump(get_included_files());