Toggle shipping method based on customer's condition

Question

I created an extension following Inchoo's tutorial but still confusing at how to toggle the shipping method.

Once customers about to see the shipping method page, I need to check the customer's attribute. If Yes the display my custom shipping method, otherwise hide. This is required for both frontend and admin placing order.

I have a few thoughts but all out of my ability to start. I need some hints about which idea is the most efficient and what files should I created:

1. Using event: set an event such as before_shipping_method_render(I made up this one), then I can setup a function in Observer.php to remove the shipping method from the collection before rendering but I don't know the event name and how to get the collection.
2. Rewriting Magento function: rewrite the function that puts all enabled shipping methods together. I can put my condition check function in the iterate then allow my custom shipping method if condition is Yes otherwise vice versa.

Answer 1

Update your module's config.xml file with the following details:

<global>
        <blocks>
            <checkout>
                <rewrite>
                    <onepage_shipping_method_available>Inchoo_Shipping_Block_Method</onepage_shipping_method_available>
                </rewrite>
            </checkout>
        </blocks>
<global>

Create a new file Inchoo/Shipping/Block/Method.php, which remove your shipping method:

<?php
class Inchoo_Shipping_Block_Method extends Mage_Checkout_Block_Onepage_Shipping_Method_Available
{
    public function getShippingRates()
    {
        $youCustomAttribute = false;
        // Check if any customer is logged in or not
        if (Mage::getSingleton('customer/session')->isLoggedIn()) {  
            // Load the customer's data
            $customer = Mage::getSingleton('customer/session')->getCustomer();   
            // mange your code to get the customer attribute 
            $youCustomAttribute = $customer->getYourCustomerAttribute();

        }
        $rates = parent::getShippingRates();
        if (array_key_exists('inchoo_shipping', $rates) && $youCustomAttribute!==false) {
            unset($rates['inchoo_shipping']);
        }

        return $rates;
    }
}

For more see here.