I solved the problem with this code by creating again de meta box:
// Add the Meta Box
function add_custom_meta_box() {
add_meta_box(
'custom_meta_box', // $id
'Product Requirements', // $title
'show_custom_meta_box', // $callback
'produktkrav', // $page
'normal', // $context
'high'); // $priority
}
add_action('add_meta_boxes', 'add_custom_meta_box');
// Field Array
$prefix = 'custom_';
$custom_meta_fields = array(
array(
'label'=> 'Filter criteria',
'desc' => 'Select the filter criteria for this product requirement.',
'id' => $prefix.'select',
'type' => 'select',
'options' => array (
'one' => array (
'label' => 'Miljo- og energikrav',
'value' => 'Miljo- og energikrav'
),
'two' => array (
'label' => 'Tildelingskriterier',
'value' => 'Tildelingskriterier'
),
'three' => array (
'label' => 'Leverandorens',
'value' => 'Leverandorens'
)
)
),
array(
'label'=> 'Mandatory Requirement',
'desc' => 'Check if this product requirement is mandatory.',
'id' => $prefix.'checkbox',
'type' => 'checkbox'
),
array(
'label' => 'Categories',
'desc' => 'Related categorie.',
'id' => $prefix.'post_id',
'type' => 'post_list',
'post_type' => array('category_product'),
)
);
// The Callback
function show_custom_meta_box() {
global $custom_meta_fields, $post;
// Use nonce for verification
echo '<input type="hidden" name="custom_meta_box_nonce" value="'.wp_create_nonce(basename(__FILE__)).'" />';
// Begin the field table and loop
echo '<table class="form-table">';
foreach ($custom_meta_fields as $field) {
// get value of this field if it exists for this post
$meta = get_post_meta($post->ID, $field['id'], true);
// begin a table row with
echo '<tr>
<th><label for="'.$field['id'].'">'.$field['label'].'</label></th>
<td>';
switch($field['type']) {
// case items will go here
// select
case 'select':
echo '<select name="'.$field['id'].'" id="'.$field['id'].'">';
foreach ($field['options'] as $option) {
echo '<option', $meta == $option['value'] ? ' selected="selected"' : '', ' value="'.$option['value'].'">'.$option['label'].'</option>';
}
echo '</select><br /><span class="description">'.$field['desc'].'</span>';
break;
// checkbox
case 'checkbox':
echo '<input type="checkbox" name="'.$field['id'].'" id="'.$field['id'].'" ',$meta ? ' checked="checked"' : '','/>
<label for="'.$field['id'].'">'.$field['desc'].'</label>';
break;
// post_list
case 'post_list':
$items = get_posts( array (
'post_type' => $field['post_type'],
'posts_per_page' => -1
));
echo '<select name="'.$field['id'].'" id="'.$field['id'].'">
<option value="">Select One</option>'; // Select One
foreach($items as $item) {
echo '<option value="'.$item->ID.'"',$meta == $item->ID ? ' selected="selected"' : '','> '.$item->post_title.'</option>';
} // end foreach
echo '</select><br /><span class="description">'.$field['desc'].'</span>';
break;
} //end switch
echo '</td></tr>';
} // end foreach
echo '</table>'; // end table
}
// Save the Data
function save_custom_meta($post_id) {
global $custom_meta_fields;
// verify nonce
if (!wp_verify_nonce($_POST['custom_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 $post_id;
}
// loop through fields and save the data
foreach ($custom_meta_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);
}
} // end foreach
}
add_action('save_post', 'save_custom_meta');``