Rewrite Admin Newsletter Grid

Question

I am trying to rewrite Grid in Magento Admin for Newsletter Subscribers. I am using code below to rewrite Grid in Custom module:

config.xml (only required part is added)

<global>    
    <blocks>
        <custommodule>
            <class>Namespace_Module_Block</class>
        </custommodule>
        <adminhtml>
            <rewrite>
                <!-- Extra column in newsletter subscribers grid  -->
                <newsletter_subscriber_grid>Namespace_Module_Block_Adminhtml_Newsletter_Subscriber_Grid</newsletter_subscriber_grid>
            </rewrite>
        </adminhtml>
        <catalog>
            <rewrite>
                <product_list_toolbar>Namespace_Module_Block_Product_List_Toolbar</product_list_toolbar>
                <product_view>Namespace_Module_Block_Product_View</product_view>
            </rewrite>
        </catalog>
    </blocks>
<global>

Namespace_Module_Block_Adminhtml_Newsletter_Subscriber_Grid

    <?php
    class Namespace_Module_Block_Adminhtml_Newsletter_Subscriber_Grid extends Mage_Adminhtml_Block_Newsletter_Subscriber_Grid 
    {
        protected function _prepareColumns()
        {
            // extra grid column added
        }
    }

But Grid is not updating in Admin... Anything wrong I am doing here...??

Answer 1

First, your configuration file should be config.xml and not config.php.

Second it must declare the module like this, this bit seems to be missing in the code you pasted:

<modules>
    <Namespace_Module>
        <version>0.0.1</version>
    </Namespace_Module>
</modules>

And the XML code must be surrounded with a <config> tag.

Now, most of the time, the main error when trying to add columns to an existing grid using block rewrite is that the extended class method calls the following:

return parent::_prepareColumns();

Calling this will call the original _prepareColumns method and thus, override the extra column you're trying to add.

To avoid that, you need to call the following instead in your custom code:

return Mage_Adminhtml_Block_Widget_Grid::_prepareColumns();

Personal Suggestion

Instead of rewriting the entire block, use an observer.

In your config.xml add the following code under the <config> tag:

<adminhtml>
    <events>
        <core_layout_block_create_after>
            <observers>
                <namespace_module_after_block>
                    <type>singleton</type>
                    <class>Namespace_Module_Model_Observer</class>
                    <method>blockCreateAfter</method>
                </namespace_module_after_block>
            </observers>
        </core_layout_block_create_after>
    </events>
</adminhtml>

Now create the following file Namespace/Module/Model/Observer.php with the following content:

<?php

class Namespace_Module_Model_Observer {
    public function blockCreateAfter(Varien_Event_Observer $observer)
    {
        $block = $observer->getBlock();

        if ($block instanceof Mage_Adminhtml_Block_Newsletter_Subscriber_Grid) {
            $block->addColumnAfter('customcolumn',
                array(
                    'header' => Mage::helper('newsletter')->__('Custom Column'),
                    'index' => 'customcolumn'
                ),
                'after_column'
            );
        }
    }
}

In this code you need to replace the after_column with the name of the original column you want to place your custom column after.