Add a meta box to ALL Pages

Question

I'd like to add a meta box to all my pages (not posts) but it looks like I am only able to add it for a specific post based on the codex?

add_meta_box( $id, $title, $callback, $page, $context = 'advanced', $priority = 'default', $callback_args = null );

Answer 1

Try this. This is part of some code I use.

 // Add meta boxes to Page
  add_meta_box( 'RelatedImage', __('Related images'), 'related_images_meta_box', 'page', 'normal', 'high' );

  function related_images_meta_box($object) { 
    $nonce = wp_create_nonce(plugin_basename( __FILE__ ));
  ?>
    <input type="hidden" name="wp_filebrowser_nonce" id="wp_filebrowser_nonce" value="<?php echo $nonce; ?>" />
    <table>
      <tr>
        <td>
          <label for="related_image" class="">Related image</label>
        </td>
        <td>
          <input type="text" id="related_image" name="related_image"  value="<?php echo 'your meta property' ?>" size="40" />  
        <td>
      </tr>
    </table>
  <?php }

Answer 2

Wordpress has the following post types by default, with your custom post types add at the end of the array:

Array
(
    [0] => post
    [1] => page
    [2] => attachment
    [3] => revision
    [4] => nav_menu_item
    [5] => ...all your custom post types
)

So you can loop through them and simply add a meta box to every post type. Note: This won't work for attachment, revision and nav_menu_item, so you want to skip them:

function wpse44962_add_meta_boxes()
{
    foreach ( array_keys( $GLOBALS['wp_post_types'] ) as $post_type )
    {
        // Skip:
        if ( in_array( $post_type, array( 'attachment', 'revision', 'nav_menu_item' ) ) )
            continue;

        // You'll have to set $id, $title, $callback yourself:
        add_meta_box( $id, $title, $callback, $post_type, 'advanced', 'default' );
    }
}
add_action( 'add_meta_boxes', 'wpse44962_add_meta_boxes' );