以重写 app/code/core/Mage/Catalog/Block/Navigation.php 为例

1. 复制Mage (不推荐使用 )

First add a new Navigation.php file you can edit to your local folder that Magento will reference instead of the original.

Copy the original found here:  app/code/core/Mage/Catalog/Block/Navigation.php

Recreate this folder structure in your app/code/local folder. So go to app/code/local, make a Mage folder, inside it make a Catalog folder, inside that make a Block folder, and inside that place your copy of Navigation.php, eg:  app/code/local/Mage/Catalog/Block/Navigation.php

Second, add some code to the app/etc/local.xml file, inside of the global tags.

Xml代码  

1. <blocks>   
2.     <catalog>  
3.         <rewrite>  
4.             <navigation>Mage_Catalog_Block_Navigation</navigation>                  
5.         </rewrite>  
6.     </catalog>  
7. </blocks>   

2. 重写 (推荐 )

If you want to override a core controller on Magento in order to add other customActions, it is really quick and easy to do so. Here are the files that you have to take into account:

• The block you want to override : /app/code/core/Mage/Catalog/Block/Navigation.php
• The xml file to enable the module: /app/etc/modules/[namespace] _All.xml
• The block xml file definition : /app/code/local/[namespace] /Catalog/etc/config.xml
• The overridden block : /app/code/local/[namespace] /Catalog/Block/Navigation.php

本文中所有 [namespace] 将被取代为我自己实例的名称 “App”，如果你想要用其他命名空间，可以替换[namespace]

First of all, you have to enable the module on the /app/etc/modules/ directory. This file would be App _All.xml and inside that:  

Xml代码  

1. <?xml version="1.0"?>  
2. <config>  
3.      <modules>  
4.         <App_Catalog>  
5.             <active>true</active>  
6.             <codePool>local</codePool>  
7.             <!--depends>  
8.                 <Mage_Core/>  
9.             </depends-->  
10.         </App_Catalog>  
11.      </modules>  
12. </config>  

开启depends的话，表示依靠core class， 

Now it’s time to create the /app/code/local/App /Catalog/etc/config.xml file that will override the core block:

Xml代码  

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <config>  
3.     <modules>  
4.         <App_Catalog>  
5.             <version>0.1.0</version>  
6.         </App_Catalog>  
7.     </modules>  
8.     <global>  
9.         <blocks>  
10.             <catalog>  
11.                 <rewrite>  
12.                         <navigation>App_Catalog_Block_Navigation</navigation>  
13.                 </rewrite>  
14.             </catalog>  
15.         </blocks>  
16.     </global>  
17. </config>  

注意：<navigation>App_Catalog_Block_Navigation</navigation> 中 App_Catalog_Block_Navigation 不能随便起名，一定要形成正确完整的路径， [namespace] _Catalog_Block_Navigation =>[namespace]/Catalog/Block/Navigation.php

Finally, we can create the class that will add/change actions to the core block:app/code/local/App/Catalog/Block/Navigation.php

Java代码  

1. <?php  
2. class App_Catalog_Block_Navigation extends Mage_Catalog_Block_Navigation  
3. {  
4.     protected function _renderCategoryMenuItemHtml($category, $level = 0, $isLast = false, $isFirst = false,  
5.         $isOutermost = false, $outermostItemClass = '', $childrenWrapClass = '', $noEventAttributes = false, $showText = false)  
6.     {  
7.        /* .... */  
8.     }  
9. }  

注意： class是继承了原来的Mage_Catalog_Block_Navigation

注意：如果要看效果，要清理cache先，或者在后台 disable cache