/app/code/core/Mage/Payment/Model/Method/Abstract.php isApplicableToQuote()

payment method类会继承Mage_Payment_Model_Method_Abstract

在模板里会判断payment method是否可以显示，供用户选择。最终会调用isApplicableToQuote()

所以自己的payment method插件可以写isApplicableToQuote()方法用来判断在哪些条件下可以显示或者不显示。

workflow:

->app/design/frontend/base/default/template/checkout/onepage/payment/methods.phtml $this->getMethods() [$this => Mage_Payment_Block_Form_Container]

->app/code/core/Mage/Payment/Block/Form/Container.php[_canUseMethod()] && app/code/core/Mage/Payment/Model/Abstract.php [isApplicableToQuote()]