Powerful block system in Magento

When you read the class Mage_Core_Block_Abstract,you will know that magento creates a very powerful block system.

First of all, Mage_Core_Block_Abstract is thesubclass of Varien_Object. That is to say, magentospecific block class whose parent classis Mage_Core_Block_Abstract can add as many childblocks as possible and access them in the array-style way.

    public functionsetChild($alias, $block)

    {

       if (is_string($block)) {

           $block =$this->getLayout()->getBlock($block);

       }

       if (!$block) {

           return$this;

       }

      $block->setParentBlock($this);

      $block->setBlockAlias($alias);

       $this->_children[$alias] =$block;

       return $this;

    }

Moreover, Magento provides two ways to use block: XML layoutway and object way.

1.Use XML layout way

<catalog_category_default>

       <referencename="left">

        <blocktype="directory/currency" name="currency"template="directory/currency.phtml"/>

       </reference>

</catalog_category_default>

In the template file, use following statement<?php echo$this->getChildHtml("currency");?>

2.Object way

<?php

$currency =new Mage_Directory_Block_Currency();

echo $currency->toHtml();

?>