By overriding template: app/design/frontend/[interface]/[theme]/template/checkout/onepage /payment/methods.phtml
By overriding method: Mage_Checkout_Block_Onepage_Payment_Methods::_canUseMethod()
By overriding method: Mage_Payment_Model_Method_Abstract::isAvailable()
By overriding method: Mage_Checkout_Block_Onepage_Payment_Methods::getMethods()
By observing event: payment_method_is_active
Among above methods obviously using event-observer technique is the best way to go.
And here I will be discussing about how to enable the PayPal (Website Standard) method only when current currency is USD.
Suppose a skeleton module(MagePsycho_Paymentfilter) has already been created.
Step 1:
Register the event: ‘payment_method_is_active’ in config.xml.
Add the following xml code in app/code/local/MagePsycho/Paymentfilter/etc/config.xml:
…
<frontend>
…
<events>
<payment_method_is_active>
<observers>
<paymentfilter_payment_method_is
_active>
<type>singleton</type>
<class>paymentfilter/observer</class>
<method>paymentMethodIsActive</method>
</paymentfilter_payment_method_is_active>
</observers>
</payment_method_is_active>
</events>
…
</frontend>
…
Step 2: Implement the observer model
Create observer file: app/code/local/MagePsycho/Paymentfilter/Model/Observer.php and paste the following code:
<?php
/**
* @category MagePsycho
* @package MagePsycho_Paymentfilter
* @author magepsycho@gmail.com
* @website http://www.magepsycho.com
* @license http://opensource.org/licenses/osl-3.0.php Open Software License (OSL 3.0)
*/
class MagePsycho_Paymentfilter_Model_Observer {
public function paymentMethodIsActive(Varien_Event_Observer $observer) {
$event = $observer->getEvent();
$method = $event->getMethodInstance();
$result = $event->getResult();
$currencyCode = Mage::app()->getStore()->getCurrentCurrencyCode();
if( $currencyCode == ‘USD’){
if($method->getCode() == ‘paypal_standard’ ){
$result->isAvailable = true;
}else{
$result->isAvailable = false;
}
}
}
}
Step 3: Go ahead for testing.