Custom Fields

<?php
add_action( 'init', 'create_product' );
function create_product() {
  $labels = array(
    'name' => _x('Products', 'post type general name'),
    'singular_name' => _x('Product', 'post type singular name'),
    'add_new' => _x('Add New', 'Product'),
    'add_new_item' => __('Add New Product'),
    'edit_item' => __('Edit Product'),
    'new_item' => __('New Product'),
    'view_item' => __('View Product'),
    'search_items' => __('Search Products'),
    'not_found' =>  __('No Products found'),
    'not_found_in_trash' => __('No Products found in Trash'),
    'parent_item_colon' => ''
  );
 
  $supports = array('title', 'revisions', 'thumbnail', 'editor');
 
  register_post_type( 'product',
    array(
      'labels' => $labels,
      'public' => true,
      'supports' => $supports
    )
  );
}
?>
<?php 
 
$meta_box = array(
    'id' => 'my-meta-box',
    'title' => 'Product Options',
    'page' => 'product',
    'context' => 'normal',
    'priority' => 'high',
    'fields' => array(
        array(
            'name' => 'Price',
            'desc' => 'Enter the price of the product starting with $.',
            'id' => 'price',
            'type' => 'text',
            'std' => ''
        ),
		array(
            'name' => 'Dimensions',
            'desc' => 'Enter the dimensions of the product.',
            'id' => 'dimensions',
            'type' => 'text',
            'std' => ''
        ),
		array(
            'name' => 'Colors',
            'desc' => 'Enter to colors seperating each value.',
            'id' => 'colors',
            'type' => 'text',
            'std' => ''
        ),
        array(
            'name' => 'Description',
            'desc' => 'Enter the description of the product here, to enter the details, write it in the large text box underneath the title.',
            'id' => 'description',
            'type' => 'textarea',
            'std' => ''
        )
    )
);
add_action('admin_menu', 'mytheme_add_box');
 
// Add meta box
function mytheme_add_box() {
    global $meta_box;
 
    add_meta_box($meta_box['id'], $meta_box['title'], 'mytheme_show_box', $meta_box['page'], $meta_box['context'], $meta_box['priority']);
}
// Callback function to show fields in meta box
function mytheme_show_box() {
    global $meta_box, $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 ($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 'price':
                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 'dimensions':
                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 'colors':
                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 'description':
                echo '<textarea name="', $field['id'], '" id="', $field['id'], '" cols="60" rows="4" style="width:97%">', $meta ? $meta : $field['std'], '</textarea>', '<br />', $field['desc'];
                break;
        }
        echo     '<td>',
            '</tr>';
    }
 
    echo '</table>';
}
add_action('save_post', 'mytheme_save_data');
 
// Save data from meta box
function mytheme_save_data($post_id) {
    global $meta_box;
 
    // 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 ($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);
        }
    }
}
?>