Adding shipping costs to cart automatically in Magento

In my case, I need to adding shipping cost of Webshopapps Matrix Rates to cart automatically. If you meet the same requirement , you can follow these steps to make it done:
1/Create a xml file to declare new module: app/etc/modules/Inbusiness_Cart.xml

<?xml version="1.0"?>
<config>
<modules>
<Inbusiness_Cart>
<active>true</active>
<codePool>local</codePool>
</Inbusiness_Cart>
</modules>
</config>

2/Create app/code/local/Inbusiness/Cart/etc/config.xml

<?xml version="1.0"?>
<config>
<modules>
<Inbusiness_Cart>
<version>1.1.1</version>
</Inbusiness_Cart>
</modules>
<global>
<models>
<Inbusiness_Cart>
<class>Inbusiness_Cart_Model</class>
</Inbusiness_Cart>
</models>
</global>
<frontend>
<events>
<checkout_cart_save_before>
<observers>
<inbusiness_set_shipping_observer>
<type>singleton</type>
<class>Inbusiness_Cart/observer</class>
<method>setShipping</method>
</inbusiness_set_shipping_observer>
</observers>
</checkout_cart_save_before>
</events>
</frontend>

</config>

3/ Create app/code/local/Inbusiness/Cart/Model/Observer.php

<?php
class Inbusiness_Cart_Model_Observer {

private $_shippingCode = 'matrixrate';
private $_country = 'NO';

public function setShipping($observer) {

/*if (Mage::registry('checkout_addShipping')) {
Mage::unregister('checkout_addShipping');
return;
}
Mage::register('checkout_addShipping',true);*/

$event = $observer->getEvent();
$cart = $event->getCart();
$rates = $cart->getQuote()->getShippingAddress()->getAllShippingRates();
$allowed_rates = array();
foreach ($rates as $rate) {
array_push($allowed_rates,$rate->getCode());
}

if (!in_array($this->_shippingCode,$allowed_rates) && count($allowed_rates) > 0) {
$shippingCode = $allowed_rates[0];
$cart->getQuote()->getShippingAddress()->setShippingMethod($shippingCode)->save();
}
return;

}

}

?>

Resource:

http://excellencemagentoblog.com/magento-shipping-method-dropdown-default-shipping-method-on-cart-page
http://www.danneh.org/2010/08/adding-shipping-costs-to-the-cart-automatically-in-magento/
http://www.nicksays.co.uk/magento-events-cheat-sheet-1-8/
Mage::dispatchEvent(‘checkout_cart_save_before’, array(‘cart’=>$this));