update layout programmatically in magento event observer

Question

I am trying to change the template(view.phtml) of a block (product.info) for product detail page, to do this, I am observing an event (controller_action_l

Answer 1

As Ben said, I don't know why you're going to put it on the observer but the problem in your case is the sequence of loadLayout.

You can check your loaded layout xml by using:

Mage::log(Mage::getSingleton('core/layout')->getUpdate()->asString());

Pretty sure your has been overridden by other setTemplate that's the reason your template is not shown.

Mage_Core_Controller_Varien_Action

public function loadLayout($handles=null, $generateBlocks=true, $generateXml=true)
{
    // if handles were specified in arguments load them first
    if (false!==$handles && ''!==$handles) {
        $this->getLayout()->getUpdate()->addHandle($handles ? $handles : 'default');
    }

    // add default layout handles for this action
    $this->addActionLayoutHandles();

    $this->loadLayoutUpdates(); //in here: $this->getLayout()->getUpdate()->load();

    if (!$generateXml) {
        return $this;
    }
    //event: controller_action_layout_generate_xml_before
    $this->generateLayoutXml(); //in here: $this->getLayout()->generateXml();

    if (!$generateBlocks) {
        return $this;
    }
    //event: controller_action_layout_generate_blocks_before, your observer is located here
    $this->generateLayoutBlocks(); //in here: $this->getLayout()->generateBlocks();
    $this->_isLayoutLoaded = true;

    return $this;
}

So, you're going to modify the xml using event: controller_action_layout_generate_blocks_before.

It means what you need to do is:

//add the update
$layout->getUpdate()->addUpdate('');
//then generate the xml
$layout->generateXml();

What cause your problem is:

$layout->getUpdate()->load();

was called again after

$layout->getUpdate()->addUpdate('');

Though it is better to use event: controller_action_layout_generate_xml_before. So that you don't need to generate your xml twice.