Get Post ID of post you're currently editing in WordPress - wordpress

Question

I'm attempting to get the ID of the post I am editing in functions.php for the purpose of dynamically rewriting a custom post type slug.
This is what I'm working with so far.
function change_post_type_slug( $args, $post_type ) {
if ( 'custom_post' == $post_type ) {
global $post;
$location = get_field('custom_field', $post->ID);
$args['rewrite']['slug'] = $location;
}
return $args;
}
add_filter( 'register_post_type_args', 'change_post_type_slug', 10, 2 );
I am not sure if the hook register_post_type_args is firing before I am able to get the ID, or if this is even the best way to go about what I am trying to accomplish. Can't find much out there on the subject.
I was able to get it to work with the following:
function change_post_type_slug( $args, $post_type ) {
if ( 'lead_page' == $post_type ) {
$post_id = $_GET['post'];
$location = get_field('leadpage_location', $post_id);
$args['rewrite']['slug'] = $location->post_name;
}
return $args;
}
add_filter( 'register_post_type_args', 'change_post_type_slug', 10, 2 );
However it resulted in a notice on the front-end:
Notice: Undefined index: post in /path/to/wordpress/functions.php on line 623
Line 623 is $post_id = $_GET['post'];

Answer 1

You should use the updated_postmeta hook for this, as its run every time you update your custom fields.
Then you can update your post data with wp_update_post() function.
add_action( 'updated_postmeta', function( $meta_id, $object_id, $meta_key, $meta_value ) {
if ( 'location' === $meta_key ) {
wp_update_post([
'ID' => $object_id,
'post_name' => $meta_value,
]);
}
}, 10, 4 );

Answer 2

Update:
Try this:
function change_post_types_slug( $args, $post_type ) {
if ( 'your-custom_post' === $post_type ) {
// Check and get the custom post ID
$id = isset($_GET[ 'post' ]) ? $_GET[ 'post' ] : '' ;
// $location = get_field('leadpage_location', $id);
$args['rewrite']['slug'] = 'new-slug-here';
}
return $args;
}
add_filter( 'register_post_type_args', 'change_post_types_slug', 10, 2 );

Answer 3

Try this out:
function change_post_type_slug( $args, $post_type ) {
if ( 'lead_page' === $post_type && is_admin() && $_GET['action'] === 'edit' ) {
$post_id = $_GET['post'];
$location = get_field('leadpage_location', $post_id);
$args['rewrite']['slug'] = $location->post_name;
}
return $args;
}
add_filter( 'register_post_type_args', 'change_post_type_slug', 10, 2 );
It adds two more conditionals, to check if you're on the admin screen and to check of there is a GET parameter of edit. Probably overkill to do is_admin() as well, but now you're super safe.