(CodeIgniter) Unable to add to Cart Class

(CodeIgniter) Unable to add to Cart Class

I've just started playing around with the shopping cart class for
CodeIgniter (version 2.1.4) and I've been following tutorials that help
explain it. But for some reason I am unable to successfully add a a simple
array to the cart.
Here is my implementation of the cart class:
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Cart extends CI_Controller {
public function __construct() {
parent:: __construct();
}
public function index() {
$nav["navigation"] = $this->getCategory->getCategories();
$this->load->view("header");
$this->load->view("scripts");
$this->load->view("nav", $nav);
$this->load->view("cart");
$this->load->view("footer");
}
function add() {
$data = array(
"id" => "42",
"name" => "pants",
"quantity" => 1,
"price" => 19.99,
"options" => array("size" => "medium")
);
$this->cart->insert($data);
var_dump($this->cart->contents()); //This should output the array!
}
function show() {
$cart = $this->cart->contents();
echo "<pre>" . print_r($cart) . "</pre>"; //Nothing here either!
}
function update() {
$this->cart->update($data);
redirect(base_url()."cart");
}
function total() {
echo $this->cart->total();
}
function remove() {
$this->cart->update($data);
}
function destroy() {
$this->cart->destroy();
}
}
But if I go to the add function the var_dump just displays "array(0) { }".
Same result if I navigate to the show function.
Here is my autoload config showing that I have autoloaded the cart library
has been loaded:
$autoload['libraries'] = array("database", "session", "cart");
$autoload['helper'] = array("html", "url", "form");
I know it's something really simple and obvious I'm missing, but right now
I'm just left baffled. Any suggestions?