在Magento Checkout Onepage 中SaveBilling处理大致可分以下几步
1、通过Ajax提交到OnePageController.php的saveBillingAction方法
   
//在billing.phtml中利用Javascript对Billing类进行创建，并在该页面中通过billing.save()来进行Ajax请求
 

 var billing = new Billing('co-billing-form', '<?php echo $this->getUrl('checkout/onepage/getAddress') ?>address/', '<?php echo $this->getUrl('checkout/onepage/saveBilling') ?>');
//javascript'save方法
save: function(){
        if (checkout.loadWaiting!=false) return;
        var validator = new Validation(this.form);
        if (validator.validate()) {
            if (checkout.method=='register' && $('billing:customer_password').value != $('billing:confirm_password').value) {
                alert(Translator.translate('Error: Passwords do not match'));
                return;
            }
            checkout.setLoadWaiting('billing');
//            if ($('billing:use_for_shipping') && $('billing:use_for_shipping').checked) {
//                $('billing:use_for_shipping').value=1;
//            }
            var request = new Ajax.Request(
                this.saveUrl,
                {
                    method: 'post',
                    onComplete: this.onComplete,
                    onSuccess: this.onSave,
                    onFailure: checkout.ajaxFailure.bind(checkout),
                    parameters: Form.serialize(this.form)
                }
            );
        }
    }

 
2、处理saveBillingAction中saveBilling方法
   
$result = $this->getOnepage()->saveBilling($data, $customerAddressId);
2.1 分析sales_flat_quote_address表中有无addressid(一条billing信息就有一个addressid与之相对应)，有则更新，无则追加

$address = $this->getQuote()->getBillingAddress();
       if (!empty($customerAddressId)) {
           $customerAddress = Mage::getModel('customer/address')->load($customerAddressId);
           if ($customerAddress->getId()) {
               if ($customerAddress->getCustomerId() != $this->getQuote()->getCustomerId()) {
                   return array('error' => 1,
                       'message' => Mage::helper('checkout')->__('Customer Address is not valid.')
                   );
               }
               $address->importCustomerAddress($customerAddress);
           }
       } else {
           unset($data['address_id']);
           $address->addData($data);
           //$address->setId(null);
       }
 $this->getQuote()->collectTotals();进行金额计算

    



展 开这个方法，会发现这个方法是在 app/code/core/Mage/Sales/Model/Quote/Address.php中定义，其内用反射来找到当前需要计算的模块，而 collect函数则在app/code/core/Mage/Sales/Model/Quote/Address/Total/下(通过 getTotalModels可以看到其命名空间)，也就是说，不管是shipping、subtotal、grand、handling fee、tax、discount等运算规则，其内的运算方法名是统一的，名为collect()。这也就是模板模式。
   

public function collectTotals()
    {
        foreach ($this->getTotalModels() as $model) {
            if (is_callable(array($model, 'collect'))) {
                $model->collect($this);
            }
        }
        return $this;
    }

3、根据用户是否选择the same as shipping information来决定执行_getShippingMethodsHtml
4、执行_getShippingMethodsHtml

返 回layout中的checkout_onepage_shippingmethod 块信息(其内有显示available.phtml与additional.phtml的信息。具体请参见layout/checkout.xml下 block=”checkout_onepage_shippingmethod”下的附属块结点所对应模板的phtml文件)
   

protected function _getShippingMethodsHtml()
  {
      $layout = $this->getLayout();
      $update = $layout->getUpdate();
      $update->load('checkout_onepage_shippingmethod');
      $layout->generateXml();
      $layout->generateBlocks();
      $output = $layout->getOutput();
      return $output;
  }

5、将块信息进行json编码，返回给opcheckout.js的savebilling的ajax

    
$result['update_section'] = array(
                        'name' => 'shipping-method',
                        'html' => $this->_getShippingMethodsHtml()
                    );
$this->getResponse()->setBody(Zend_Json::encode($result));

6、在opcheckout.js中 savebilling成功后调用onSave,而onSave指向的是nextstep函数

nextStep: function(transport){
        if (transport && transport.responseText){
            try{
                response = eval('(' + transport.responseText + ')');
            }
            catch (e) {
                response = {};
            }
        }
        if (response.error){
            if ((typeof response.message) == 'string') {
                alert(response.message);
            } else {
                if (window.billingRegionUpdater) {
                    billingRegionUpdater.update();
                }
                alert(response.message.join("/n"));
            }
            return false;
        }
        checkout.setStepResponse(response);
}
//而checkout.setStepResponse(response)为基类checkout的方法
  setStepResponse: function(response){
        if (response.update_section) {
            //response.update_section.html
            $('checkout-'+response.update_section.name+'-load').update(response.update_section.html);
        }
//这里的response.update_section.html就是返回在服务器端返回的json,其格式如下{"update_section":{"html":"<div>...</div>"}}

   
其它模块类似。