Adding meta boxes to custom post type

Question

The add_meta_box() function needs a callback function as an argument to display the meta box on the edit page of a custom type post. My problem is I can not display anything, say in the input type=text (for example the values of an already posted post), because I don't have the ID of the post...

get_post_meta needs the ID of the post to display the values!

How can I get the ID of the post?

Answer 1

Let’s say your post type is named product. You register your metabox with …

add_action( 'add_meta_boxes_product', 'register_product_metabox' );

function register_product_metabox()
{
    // register the metabox
}

You get the post id in your callback per post object now:

function metabox_callback( $post )
{
    $field = get_post_meta( $post->ID );
}

This happens because WordPress calls the callback with:

call_user_func($box['callback'], $object, $box);

See wp-admin/includes/template.php.