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

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

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

    
        
            
                
                    
                    mymodule/adminhtml_observer
                    onBlockHtmlBefore
                
            
        
    

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 :)