Magento : How to add onchange function in country in Cart page?

Question

I want to add onchange function in select of country in cart page. But country are coming from :

Mage::getBlockSingleton('directory/data')->getCountryHtmlSelect($this->getEstimateCountryId())

So , How to add onchange function to country on Cart page.

When customer select country then page will reload and display delivery method in dropdown and calculate estimate shipping cost and add in grand total in cart page.

Answer 1

This is the function you are referring. At the end, select html is built by core/html_select block

public function getCountryHtmlSelect($defValue=null, $name='country_id', $id='country', $title='Country')
{
    Varien_Profiler::start('TEST: '.__METHOD__);
    if (is_null($defValue)) {
        $defValue = $this->getCountryId();
    }
    $cacheKey = 'DIRECTORY_COUNTRY_SELECT_STORE_'.Mage::app()->getStore()->getCode();
    if (Mage::app()->useCache('config') && $cache = Mage::app()->loadCache($cacheKey)) {
        $options = unserialize($cache);
    } else {
        $options = $this->getCountryCollection()->toOptionArray();
        if (Mage::app()->useCache('config')) {
            Mage::app()->saveCache(serialize($options), $cacheKey, array('config'));
        }
    }
    $html = $this->getLayout()->createBlock('core/html_select')
        ->setName($name)
        ->setId($id)
        ->setTitle(Mage::helper('directory')->__($title))
        ->setClass('validate-select')
        ->setValue($defValue)
        ->setOptions($options)
        ->getHtml();

    Varien_Profiler::stop('TEST: '.__METHOD__);
    return $html;
}

The good news for you are core/html_select block allows including some extra data, such as you want, using setExtraParams() method

For instance, take a look at Mage_Checkout_Block_Onepage_Abstract::getCountryHtmlSelect() method

public function getCountryHtmlSelect($type)
{
    $countryId = $this->getAddress()->getCountryId();
    if (is_null($countryId)) {
        $countryId = Mage::helper('core')->getDefaultCountry();
    }
    $select = $this->getLayout()->createBlock('core/html_select')
        ->setName($type.'[country_id]')
        ->setId($type.':country_id')
        ->setTitle(Mage::helper('checkout')->__('Country'))
        ->setClass('validate-select')
        ->setValue($countryId)
        ->setOptions($this->getCountryOptions());
    if ($type === 'shipping') {
        $select->setExtraParams('onchange="if(window.shipping)shipping.setSameAsBilling(false);"');
    }

    return $select->getHtml();
}