private static void on_contact_created(IntPtr list, IntPtr lf)
        {
            FriendList         thiz     = fromNativePtr <FriendList>(list);
            FriendListListener listener = thiz.Listener;

            listener.on_contact_created_public?.Invoke(thiz, fromNativePtr <Friend>(lf));
        }
        private static void on_contact_updated(IntPtr list, IntPtr newFriend, IntPtr oldFriend)
        {
            FriendList         thiz     = fromNativePtr <FriendList>(list);
            FriendListListener listener = thiz.Listener;

            listener.on_contact_updated_public?.Invoke(thiz, fromNativePtr <Friend>(newFriend), fromNativePtr <Friend>(oldFriend));
        }
        private static void on_sync_status_changed(IntPtr list, int status, string msg)
        {
            FriendList         thiz     = fromNativePtr <FriendList>(list);
            FriendListListener listener = thiz.Listener;

            listener.on_sync_status_changed_public?.Invoke(thiz, (FriendListSyncStatus)status, msg);
        }