Custom post type, have only my meta boxes

Question

I am working on a plugin for which I create a custom post type and several meta boxes on the post page.

However, the theme that I have seems to be adding an ad meta box (Upgrade to our premium theme etc) on the pages of all custom post types.

I consider this an abuse and I don't want that meta box or any other external meta boxes on my post type page, just the ones that I add.

How can I clear all meta boxes except my own?

Edit: I am looking for a general approach to this. If I deploy my plugin to the public, I want to be sure that on my post's page there are no other meta boxes from other themes and plugins, if possible.

Answer 1

You can use remove_meta_box() to accomplish that.

To use remove_meta_box() you will need 3 pieces of information:

1. the id of the meta box you want to remove
2. the screen (or screens) you want it removed from
3. the context it was added in (e.g., 'side', 'normal', etc)

To get these 3 pieces of info, search thru the source for the theme for add_meta_box() call(s) that are used to add the meta box.

And in case it's not obvious, make sure you call remove_meta_box() in an action that is fired after whatever action the meta box was added in.

For example, if the theme looks like:

add_action ('after_theme_setup', 'add_theme_meta_boxes') ;

function
add_theme_meta_boxes ()
{
    add_meta_box ('ad-to-upgrade-to-pro', 'Upgrade to Pro', 'render_upgrade_ad', 'post', 'normal', 'high') ;

    return ;
}

The your plugin should contain the following:

// make sure you hook to an action that is fired *after* the meta box was added
add_action ('init', 'remove_theme_ad_meta_box') ;

function
remove_theme_ad_meta_box ()
{
    remove_meta_box ('ad-to-upgrade-to-pro', 'post', 'normal') ;

    return ;
}

Edit

To answer the question asked in comment: it is not possible to absolutely guarantee that no other theme/plugin adds meta boxes.

Besides, with an open system like WP, it is not a good idea to do what you are trying to do (IMHO). There are a whole host of "general purpose" plugins out in the wild that have legitimate reasons for adding meta boxes to your CPT's post{,-new}.php screens.

For example, the WordPress SEO plugin adds a meta box to any post type that is "viewable" that allows adding SEO-related metadata to the public page for posts (note: mention of WordPress SEO is not meant as an endorsement, it's just the 1st one that came to mind).

Answer 2

In addition to the above answer. There are globals available for the existing meta boxes. You can also find the latest action/filter hook available on your CPT's (probably do_meta_boxes) and just remove everything.

Global: global $wp_meta_boxes;

Take a look at the remove_meta_box function for how it works: https://developer.wordpress.org/reference/functions/remove_meta_box/

So it will be something like this:

add_action( 'do_meta_boxes', 'my_metabox_hack', 99, 3 );

function my_metabox_hack( $post_type, $cur_context, $post ) {
    global $wp_meta_boxes;

    $screen_id = 'YOUR_SCREEN_ID';
    // Remove anything there
    foreach ( $wp_meta_boxes[$screen_id] as $context => $priorities ) {
        if ( $context !== $cur_context ) {
            continue;
        }
        if ( empty( $priorities ) ) {
            $wp_meta_boxes[$screen_id][$context] = array();
            continue;
        }
        foreach ( $priorities as $priority => $metabox_id ) {
            $wp_meta_boxes[$screen_id][$context][$priority] = array();
        }
    }

    // Now add your own metaboxes bases on the $cur_context parameter.
    // add_meta_box( $id, $title, $callback, $screen, etc.... )
}

Keep in mind that this clobal contains ALL meta boxes, not just for CPT's!

I consider this a hack so please be very carefull when using this approach. It's NOT WP code standards and when not used properly it can break other plugins/functions.

EDIT: I also added an action priority. You can set it even higher to make sure this action is done as last.

EDIT2 Also keep in mind that this action could be fires multiple times and has 3 parameters for each $context. Modified the code for reflect this.