Menu of categories "not included in navigation bar" - magento

Question

If I am right, in Magento the renderCategoriesMenuHtml() function helps in displaying the menu of "categories included in the navigation menu bar".
I'd like to modify the renderCategoriesMenuHtml() function to display the menu of "categories that are not included in the navigation menu bar".
In short, I need to display a menu of categories that have the attribute "Include in navigation menu" set to no in the admin panel.
Thanks in advance.

Answer 1

Magento has a facility for changing or adding to functionality of classes known as class overrides or class rewrites. The following example assumes a namespace of "Custom" and a module name of "Nav".
First, register a module:
<?xml version="1.0" encoding="UTF-8"?>
<!-- app/etc/modules/whatever.xml -->
<config>
<modules>
<Custom_Nav><!-- must match your namespace & module folder names -->
<active>true</active>
<codePool>local</codePool>
</Custom_Nav>
</modules>
</config>
Based on the above, the application will look for a configuration file for your module:
<?xml version="1.0" encoding="UTF-8"?>
<!-- app/code/local/Custom/Nav/etc/config.xml -->
<config>
<global>
<blocks>
<catalog>
<rewrite>
<navigation>Custom_Nav_Block_Rewrite_Navigation</navigation>
</rewrite>
</catalog>
</blocks>
</global>
</config>
What this does is to rewrite the class name in the block creation factory method. The catalog navigation block is added in catalog.xml layout update XML (<block type="catalog/navigation" .../>). The above xpath will cause the class name to map to Custom_Nav_Block_Rewrite_Navigation rather than the usual Mage_Catalog_Block_Navigation, and it is this class which will be instantiated.
The final step is to create the class definition, extending from the original class for the sake of maintainability and to obey DRY:
<?php
/* app/code/local/Custom/Nav/Block/Rewrite/Navigation.php */
class Custom_Nav_Block_Rewrite_Navigation extends Mage_Catalog_Block_Navigation
{
//custom method overrides & additions belong here
}
Clear the config & block_html caches and the changes should be visible. To verify, enable template path hints + block class names via the admin panel, or create a simple script in the site root:
<?php
/* test.php in Magento root folder */
ini_set('display_errors',true);
include 'app/Mage.php';
Mage::setIsDeveloperMode(true);
Mage::app();
var_dump(Mage::getConfig()->getBlockClassName('catalog/navigation'));
Point the browser to http://site.com/test.php and the output should show the rewritten class name.