how to display enable/disable(multi select) custom shipping methods at admin side?

Question

I created custom shipping methods using following link

http://www.smashingmagazine.com/2014/01/15/create-custom-shipping-methods-magento/

Now I want enable /disable option(multiselect) at system->configuration->shipping methods->custom carrier

(For example ups carrier->allowed methods multiselect field in system configuration->shipping methods).

In order to get I'm using following code in system.xml

<allowed_methods translate="label">
    <label>Allowed Methods</label>
    <frontend_type>multiselect</frontend_type>
    <source_model>smashingmagazine_mycarrier/source_methods</source_model>
    <sort_order>20</sort_order>
    <show_in_default>1</show_in_default>
    <show_in_website>1</show_in_website>
    <show_in_store>0</show_in_store>
    <can_be_empty>1</can_be_empty>
 </allowed_methods>

and I created Methods.php in proper place.

class SmashingMagazine_MyCarrier_Model_Source_Methods
{
    public function toOptionArray()
    {

        $arr = array();
//how to get created custom shipping methods here?

        return $arr;
    }
}

Answer 1

This post on Stackoverflow is exactly what you are looking for.

Copied from the answer:

public function toOptionArray($isMultiSelect = false)
{
    $methods = Mage::getSingleton('shipping/config')->getActiveCarriers();

    $options = array();

    foreach($methods as $_code => $_method)
    {
        if(!$_title = Mage::getStoreConfig("carriers/$_code/title"))
            $_title = $_code;

        $options[] = array('value' => $_code, 'label' => $_title . " ($_code)");
    }

    if($isMultiSelect)
    {
        array_unshift($options, array('value'=>'', 'label'=> Mage::helper('adminhtml')->__('--Please Select--')));
    }

    return $options;
}

Answer 2

In case you would like to disable (or enable) multishipping for your custom shipping method, you can use this code in your Model/Carrier.php

public function collectRates(Mage_Shipping_Model_Rate_Request $request) {
    if (Mage::app()->getRequest()->getControllerName() === 'multishipping') {
        return false;
    }
    <...code...>
}