Override core block in magento

The simplest way to override a core block is to simply copy the file into the corresponding /app/code/local/ folder, and Magento automatically uses that version of the file without an XML/config changes needed.

So just copy /app/code/core/Mage/Checkout/Block/Cart/Item/Renderer.php into /app/code/local/Mage/Checkout/Block/Cart/Item/ and be sure to refresh the cache.

Magento: Redirect functions

The redirect functions are present in Mage_Core_Controller_Varien_Action class.

/* Redirect to certain url */
_redirectUrl($url)

/* Redirect to certain path */
_redirect($path, $arguments=array())

/* Redirect to success page */
_redirectSuccess($defaultUrl)

/* Redirect to error page */
_redirectError($defaultUrl)

/* Set referer url for redirect in response */
_redirectReferer($defaultUrl=null)

/* Identify referer url via all accepted methods (HTTP_REFERER, regular or base64-encoded request param) */
_getRefererUrl()

/* Check url to be used as internal */
_isUrlInternal($url)

Create custom module in magento

1) Create directory app\code\local\mymodulepack. Here ‘mymodulepack’ will be the new directory folder where you can create modules.
2) Create module named ‘MyModule’ in above defined directory path. This will be your module directory which will contain required files like models, blocks, controllers etc.
3) Now add your new module xml file in app/etc/modules/ mymodulepack _All.xml. Consider that _All.xml will be used to add all new module definitions to the same file instead of cluttering the etc/modules folder with many files.
4) Following defined code is used to inform Magento that there is an active module (you can turn it off from here by setting ‘active’ to false). Also that it is located in the ‘local’ code pool.
<?xml version="1.0"?>
<config>
<modules>
<mymodulepack_MyModule>
<active>true</active>
<codePool>local</codePool>
</mymodulepack_MyModule>
</modules>
</config>
5) Now you can enable or disable this module at Admin -> System -> Advanced. Here you can see your new module ‘Mymodulepack_MyModule’ listed there with status enable.
Note : Please disable the cache from admin section to view the module.
6) And now create the block php class file at app/code/local/mymodulepack/MyModule/Block/Myview.php which contains a function that returns the string ‘Hello World’.
<?php
class mymodulepack_MyModule_Block_Myview extends Mage_Core_Block_Template
{
public function __construct()
{
parent::__construct();
$this->setTemplate('mymodule/myview.phtml');
}
protected function _prepareLayout()
{
parent::_prepareLayout();
}
}
?>
7) Now make a config.xml file in app\code\local\mymodulepack\MyModule\etc directory. This is done to enter configuration information for the module.
<?xml version="1.0" encoding="iso-8859-1"?>
<config>
<modules>
<mymodulepack_MyModule>
<version>0.1.0</version>
</mymodulepack_MyModule>
</modules>
<blocks>
<MyModule>
<rewrite>
<MyModule>mymodulepack_MyModule_Block_Myview</MyModule>
</rewrite>
</MyModule>
</blocks>
<frontend>
<routers>
<MyModule>
<use>standard</use>
<args>
<module>mymodulepack_MyModule</module>
<frontName>MyModule</frontName>
</args>
</MyModule>
</routers>
<layout>
<updates>
<MyModule>
<file>MyModule.xml</file>
</MyModule>
</updates>
</layout>
</frontend>
<global>
<helpers>
<extras>
<class>mymodulepack_MyModule_Helper_Data</class>
</extras>
</helpers>
</global>
</config>
8) Create the php class file at app/code/local/mymodulepack/MyModule/ Helper / Data.php
<?PHP
class mymodulepack_MyModule_Helper_Data extends Mage_Core_Helper_Abstract {
}
?>
9) Now we need to create a template file which uses the View Block Class to display the message “Hello World”. Create a template (phtml) called myview.phtml in the following directory:
app/design/frontend/default/your theme/template/mymodule/myview.phtml.
<div>
<span style=" color:#0000FF; font:Arial, Helvetica, sans-serif;">
<bold><?php
echo "Hello World";
?></bold>
</span>
</div>
10)The module is now ready for use.
Where do I put this block? Should I create new mymodule.xml in theme/layout?
You can view the output by two ways.
1) {{block type=”mymodulepack_mymodule/view” template=”mymodule/myview.phtml” }}
call this block in page.xml file
2) Create xml file in app/design/frontend/default/your theme/layout/MyModule.xml
<?xml version="1.0"?>
<layout>
<default>
<reference name="content">
<action method="setTemplate"><template>page/2columns-right.phtml</template></action>
</reference>
<reference name="content">
<block type="core/template" name="mymodule" template="mymodule/myview.phtml" />
</reference>
</default>
</layout>
Note : Set the position of your module as per your requirement,
1. <reference name="right">
2. <reference name="left">
3. <reference name="content">