I have a PlugIn which lets a user upload an image to a user profile in the backend. Now I want to access the user id in the uploader to change the filename of the uploaded image.

On the user profile edit page, I get the id via global $profileuser. But when I access it in a function I added as a filter to wp_handle_upload, $profileuser is empty.

Any ideas how to get the profile user (not the logged in user) in this case?

This is my code:

add_filter('wp_handle_upload_prefilter', 'my_pre_upload', 2);

function my_pre_upload($file){
    // get current user
    global $profileuser;
    $myAuthorImg = get_userdata( $profileuser->ID );
    $myAuthorImg = 'author-' . $myAuthorImg . '.jpg";
    $file['name'] = $myAuthorImg 
    return $file;
}