overriding a magento block in multiple modules (and how to ignore the other ones)

Question

In Magento you can override a block (or helper, or model, etc.) from one module in another one (most common from Magento Adminhtml module). Now I have the problem that I wan

Answer 1

If you set your module to 'depend' on the one that's also doing a rewrite, your config will be read last and the rewrite should stick, in the appropriate file within app/etc/modules you should have:

<config>
  <modules>
    <Your_Module>
      <active>true</active>
      <codePool>local</codePool>
      <depends>
        <Other_Module/>
      </depends>
    </Your_Module>
  <modules>
<config>

Answer 2

Instead of rewriting catalog_product_grid, why not extend on Symmetrics_DeliveryTime_Block_Adminhtml_Catalog_Product_Grid? That way the Symmetrics module will keep all it's functionalities and you can add yours.

So instead of:

<blocks>
    <adminhtml>
        <rewrite>
                <catalog_product_grid>Symmetrics_DeliveryTime_Block_Adminhtml_Catalog_Product_Grid</catalog_product_grid>
        </rewrite>
    </adminhtml>
</blocks>

do this:

<blocks>
    <adminhtml>
        <rewrite>
                <deliverytime_catalog_product_grid>Namespace_MyModule_Block_Adminhtml_Catalog_Product_Grid</deliverytime_catalog_product_grid>
        </rewrite>
    </adminhtml>
</blocks>

Of course than a depend in your app/etc/modules file would be fitting.

Answer 3

The best way to overcome this problem using, layout after or before observer.

app/code/local/My/Module/etc/config.xml

<config>
<adminhtml>
    <events>
        <core_block_abstract_prepare_layout_before>
            <observers>
                <mymodule>
                    <!-- Add column to catalog product grid -->
                    <class>mymodule/adminhtml_observer</class>
                    <method>onBlockHtmlBefore</method>
                </mymodule>
            </observers>
        </core_block_abstract_prepare_layout_before>
    </events>
</adminhtml>

or can use event: core_block_abstract_prepare_layout_after.

And in Observer:

class My_Module_Model_Adminhtml_Observer
 {
   public function onBlockHtmlBefore(Varien_Event_Observer $observer) {
    $block = $observer->getBlock();
    if (!isset($block)) return;

    switch ($block->getType()) {
        case 'adminhtml/catalog_product_grid':  //or here you can put any other block 

            /*For example i am using Mage_Adminhtml_Block_Catalog_Product_Grid, and want  to add a column*/

            $block->addColumn('COLUMN_ID', array(
                'header' => Mage::helper('mymodule')->__('COLUMN HEADER'),
                'index'  => 'COLUMN_ID',
            ));
             break;

            case 'adminhtml/catalog_product_edit_tabs':

             /*Or i want to add new tab to admin product edit*/
              /* @var $block Mage_Adminhtml_Block_Catalog_Product_Edit_Tabs */
            $block->addTab('tab_name', array(
                        'label'     => Mage::helper('catalog')->__('Tab Tilte'),
                        'content'   => $block->getLayout()->createBlock('modulename/adminhtml_product_edit_tabname')->toHtml(),
                        'after'     => 'inventory',
            ));
            break;
    }
  }
}

While adding tab then you can take reference of product edit tabs to add your form fields into that using you module.

Hope this will be helpful to some one :)

Answer 4

I took a look in the class loading, and it doesn't look like there is a clean solution. The relevant classname loading code is this:

    if (isset($this->_classNameCache[$groupRootNode][$group][$class])) {
        return $this->_classNameCache[$groupRootNode][$group][$class];
    }

    ...

    if (isset($config->rewrite->$class)) {
        $className = (string)$config->rewrite->$class;

So it looks like there is no such thing as a rewritten-rewrite. The one that gets put into the configuration array is the one that gets loaded, and once cached it simply gets returned as requested. I don't see an easy way to hack the cache, either. You could try to get precedence for your module (by renaming it alphabetically, I assume), but that's a total hack and likely to fail mysteriously later on. That kills the config possibilities.

Also obnoxious: it looks like Magento only requests that grid in two places, within Mage_Adminhtml_Block_Catalog_Product (which you can easily override), but also in Mage_Adminhtml_Catalog_ProductController (d'oh!). Depending on your use case, consider overriding the catalog product block and replacing the _prepareLayout() function with your own. If you want to override the controller as well, you'll want to create your own controller (which descends from Mage_Adminhtml_Catalog_ProductController) and define a rewrite within your configuration to direct admin/catalog/product/grid to your action. A pain, but at least accomplishes your goal.

Hope that helps,

Joe