Extending Adminhtml blocks class _prepareCollection

Question

I am trying to override a adminhtml block and I created all files accordingly. The problem is that it does not have any effect. My files are as follows:

app/code/local/Grando/Groupfilter/etc/config.xml

<?xml version="1.0"?>

<config>

<modules>

    <Grando_Groupfilter>

        <version>1.0</version>

    </Grando_Groupfilter>

</modules>

<global>
    <blocks>
    <grando_groupfilter>
        <class>Grando_Groupfilter_Block</class>
    </grando_groupfilter>
        <adminhtml>
            <rewrite>
                <catalog_product_edit_tab_super_group>Grando_Groupfilter_Block_Adminhtml_Catalog_Product_Edit_Tab_Super_Group</catalog_product_edit_tab_super_group>
            </rewrite>
        </adminhtml>
    </blocks>
</global>   

</config>

app/code/local/Grando/Groupfilter/Block/Adminhtml/Catalog/Product/Edit/Tab/Super/Group.php

class Grando_Groupfilter_Block_Adminhtml_Catalog_Product_Edit_Tab_Super_Group extends Mage_Adminhtml_Block_Catalog_Product_Edit_Tab_Super_Group {
   protected function _prepareCollection()
{
    //somecodehere
} 
   }

app/etc/modules/Grando_Groupfilter.xml

    <?xml version="1.0"?>
<config>
    <modules>
        <Grando_Groupfilter>
            <active>true</active>
            <codePool>local</codePool>
        </Grando_Groupfilter>
    </modules>
</config>

Is it not possible to do this? Am I missing something?

Answer 1

Why it is not working!!! Please see below

your function is inherited from below function which is protected. Yes, we can inherit protected function into our custom module but here slite difference is that we can not inherit private property.

protected function _prepareCollection()
    {
        $allowProductTypes = array();
        $allowProductTypeNodes = Mage::getConfig()
            ->getNode('global/catalog/product/type/grouped/allow_product_types')->children();
        foreach ($allowProductTypeNodes as $type) {
            $allowProductTypes[] = $type->getName();
        }

        $collection = Mage::getModel('catalog/product_link')->useGroupedLinks()
            ->getProductCollection()
            ->setProduct($this->_getProduct())
            ->addAttributeToSelect('*')
            ->addFilterByRequiredOptions()
            ->addAttributeToFilter('type_id', $allowProductTypes);

        if ($this->getIsReadonly() === true) {
            $collection->addFieldToFilter('entity_id', array('in' => $this->_getSelectedProducts()));
        }
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }

->setProduct($this->_getProduct()) this is the function which is private So we can not set current product object.That's why your code is not working. Just make it app/code/local/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Super/Group.php