you can use call back function, like this
$this->form_validation->set_rules('userfile', 'Document', 'callback_file_selected_test');
if ($this->form_validation->run() == FALSE) {
//error
}
else{
// success
}
function file_selected_test(){
$this->form_validation->set_message('file_selected_test', 'Please select file.');
if (empty($_FILES['userfile']['name'])) {
return false;
}else{
return true;
}
}