reorder

If you make a Files view a draggable view, with an integer field and using the FieldAPI handler, everything looks great except for this error:

Undefined property stdClass::$nid in draggableviews_handler_fieldapi->get() draggableviews_handler_fieldapi.inc

and the fact that it doesn't work at all.

If you just want to insert something first in an array, as to make sure that your validation function is called first, you can do something like this:

AJAX sorting of book pages is built into Drupal's book module.

Navigate to Content Management » Books » List, and click "edit and order titles" for the book you care about.
admin/content/book/[nid-of-book-parent]