Codeigniter - input type file as required field

I have create a form with 2 file upload fields and basically I want to make them required fields. I created a call back function but just can't seem to make it work properly. It is using the callback and posts the error if some other fields are left blank but sends the form whether files are attached or not. I'm pretty new to Codeigniter. Any help would be very much appreciated!

Controller:

class Form extends CI_Controller {

function index()
{
    $this->load->helper(array('form', 'url'));

    $this->load->library('form_validation');

    //Upload errors array
    $up_errors = array();

    $this->form_validation->set_rules('first_name', 'First Name', 'required|alpha');
    $this->form_validation->set_rules('last_name', 'Surname', 'required|alpha');
    $this->form_validation->set_rules('dob', 'Date of Birth', 'required');
    $this->form_validation->set_rules('nationality', 'Nationality', 'required|alpha');
    $this->form_validation->set_rules('gender', 'Gender', 'required');
    $this->form_validation->set_rules('address_l1', 'Address Line 1', 'required|alpha_dash_space');
    //$this->form_validation->set_rules('address_l2', 'Address Line 2', 'alpha');
    $this->form_validation->set_rules('address_city', 'City', 'required|alpha');
    $this->form_validation->set_rules('address_postcode', 'Post Code', 'required|alpha_dash_space');
    //$this->form_validation->set_rules('address_country', 'Country', 'required|alpha_dash_space');
    $this->form_validation->set_rules('e_address', 'Email Address', 'required|valid_email');
    $this->form_validation->set_rules('h_tel', 'Home Telephone Number', 'required|numeric');
    $this->form_validation->set_rules('mobile', 'Mobile Number', 'required|numeric');
    $this->form_validation->set_rules('university', 'University', 'required|alpha_dash_space');
    $this->form_validation->set_rules('campus', 'Campus Name', 'required|alpha_dash_space');
    $this->form_validation->set_rules('course', 'Course Title', 'required|alpha_dash_space');
    $this->form_validation->set_rules('end_date', 'Course End Date', 'required');
    //Custom callback
    $this->form_validation->set_rules('file', 'Attachment', 'callback_handle_upload');
    //Check if file attached
    //if (isset($_FILES['file']))
    //{


    //}

    if ($this->form_validation->run() == FALSE)
    {
        $this->load->view('home');
    }
    else
    {

        //Display Success page
        $this->load->view('formsuccess');



        //Array helper
        $this->load->helper('array');





        //Set form data array
        $fields = $this->input->post('first_name')."\n".
        $this->input->post('last_name')."\n".
        $this->input->post('dob')."\n".
        $this->input->post('nationality')."\n".
        $this->input->post('gender')."\n".
        $this->input->post('address_l1')."\n".
        $this->input->post('address_l2')."\n".
        $this->input->post('address_city')."\n".
        $this->input->post('address_postcode')."\n".
        $this->input->post('address_country')."\n".
        $this->input->post('e_address')."\n".
        $this->input->post('h_tel')."\n".
        $this->input->post('mobile')."\n".
        $this->input->post('university')."\n".
        $this->input->post('campus')."\n".
        $this->input->post('course')."\n".
        $this->input->post('end_date');

        $msg = serialize($fields);

        //Upload files to server
        $this->load->library('upload');

        //Send Email
        $this->load->library('email');

        //Set config
        $config['upload_path']   = './attachments'; //if the files does not exist it'll be created
        $config['allowed_types'] = 'gif|jpg|png|doc|docx|txt|pdf';
        $config['max_size']   = '4000'; //size in kilobytes
        $config['encrypt_name']  = TRUE;

        $this->upload->initialize($config);

        $uploaded = $this->upload->up(FALSE); //Pass true if you want to create the index.php files


        //Attach the 2 files to email
        foreach($_FILES as $key => $value)
        {
            //var_dump($uploaded['success'][$key]['full_path']); //FOR TESTING
            $file = $uploaded['success'][$key]['full_path'];
            $this->email->attach($file);
            //unlink($file);
        }

        //var_dump($msg); //FOR TESTING
        $this->email->from($this->input->post('e_address'),$this->input->post('first_name') . $this->input->post('last_name'));
        $this->email->to('[email protected]'); 

        $this->email->subject('NON-SHU STUDENT REQUEST');
        $this->email->message($msg);    

        $this->email->send();

        //echo $this->email->print_debugger();
    }
}
function alpha_dash_space($str_in)
{
    if (! preg_match("/^([-a-z0-9_ ])+$/i", $str_in)) {
    $this->form_validation->set_message('_alpha_dash_space', 'The %s field may only contain alpha-numeric characters, spaces, underscores, and dashes.');
    return FALSE;
    } else {
    return TRUE;
}
}
 function handle_upload()
{
    if (count($_FILES['file']['name'] < 2)
    {
        // throw an error because nothing was uploaded
        $this->form_validation->set_message('handle_upload', "You must attach both files!");
        return false;
    }
    else
    {
        return TRUE;
    }
}

} ?>