I have a
managed_file form element. I want to trigger an AJAX callback when a user clicks the upload button. But I can't seem to get anything working by attaching the
#ajax element to the
managed_file element. I know the
managed_file element creates an upload button automatically, so I tried to hook into that using
hook_form_alter but the button doesn't seem to have been created yet, so I can't attach the AJAX handler.