current_post not working – give me -1 for every post

I try to get the current post index number and echo the number of this lesson(post)in a series of lessons(category).

I’m inside the loop on single.php page

my code looks like this:

$args = array(
   'cat' => 22,
);
$query = new WP_Query( $args );

echo $query->current_post;
echo $query->post_count;

the “$query->post_count” works great and give me the number of the posts that are inside this category,
but the “$query->current_post” don’t work and give me “-1” all the time in every post…

what i’m doing wrong?