This may be more suited for StackExchange, so if you think that would be the right place to direct my question - please let me know :).

So, I have a class with a property of save_list. This is an 2D array with it's values being in the format array('meta_key' => $meta_key). This class is instantiated once as $metabox within my functions.php file, and thereafter the $metabox variable is used to keep reference the object.

My problem is, when it comes to the save_post action, the object seems to lose it's save_list property, in that attempting to dump it shows an array with no values.

class Metabox
    public function __construct() {
        $this->save_list = array();
        add_action('save_post', array($this, 'save_postmeta'));

    public function text($meta_key, $atts) {
        global $post;

        $this->save_list[] = array('meta_key' => $meta_key);
        $default_atts = array(
            'value' => false,
            'class' => ''
        $atts = $atts + $default_atts;
        $atts['value'] = (!$atts['value']) ? get_post_meta($post->ID, $meta_key, true) : $atts['value'];

        <input name="<?php echo $meta_key; ?>" type="text" class="<?php echo $class; ?>" value="<?php echo $value; ?>">

    public function save_postmeta($post_id) {
        $save_list = $this->save_list;
        foreach ($save_list as $item) {
            $meta_key = $item['meta_key'];
            update_post_meta($post_id, $meta_key, $_POST[$meta_key]);


However, the call to print_r($this->save_list) within the text() method works fine, and keeps scope accordingly, e.g. every call of it adds to the value of save_list when dumped with that call.

I'm wondering if this has something to do with how the save_post action works, or perhaps I'm extremely tired and have made a simple, mundane error.

Any help would be greatly appreciated!

(If you think it would help for context, my functions.php file)

$metabox = new Metabox;
function add_input_metabox() {
    add_meta_box('text1', 'text1', 'input_metabox_callback', 'eating', 'side');
    add_meta_box('text2', 'text2', 'input_metabox_callback_', 'eating', 'side');
add_action('add_meta_boxes', 'add_input_metabox');

function input_metabox_callback() {
    global $metabox;
    $metabox->text('text3', array('class' => 'widefat'));
    $metabox->text('text4', array('class' => 'widefat'));

function input_metabox_callback_() {
    global $metabox;
    $metabox->text('text1', array('class' => 'widefat'));
    $metabox->text('text2', array('class' => 'widefat'));

$metabox is not in the global scope, that is why your two functions is not working. If you turn debug on you will get a a lot of debugging notice error messages regarding the use of $metabox. Simply doing the following

$metabox = new Metabox;

doesn't make a variable global. It need to be defined as a global. But before you go on and do this, take into consideration that it is recommended to stay out of the global scope, specially with an easy-to-recreate variable like $metabox.

Just think about this, you have two plugins using the same variable $metabox. This works great. Now, you define $metabox as a global in your theme. This changes the values for all instances of $metabox which leads to your plugins using wrong data and failing in what it should do.


Create yourself a "global function" which you can reuse, something like

function metabox_global_function()
    $metabox = new Metabox;
    return $metabox;

Then you can use metabox_global_function(); anywhere in any function.

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