How to tell which layout handle a block method is called from

Question

I have a little module that compiles JavaScript modules. I want to add a feature so that it compiles JavaScript files that are added to the default handle separately. I want to know if this will make performance better, because the modules common to every page can be cached, and only the modules specific to each page loaded on every request.

The best way I can think of to do this, is to use the same interface (my block has a method addModule), but to somehow work out whether it was called in the default handle or not.

Is this even possible? I feel like it ought to be, but I'm having some trouble knowing where to look, and the internet isn't being entirely helpful in this.

Answer 1

I went through this with one of my colleagues, and he was very helpful in pointing me in the right direction, and I finally got somewhere. Magento does store a parsed version of its layout tree, replete with handles. Unfortunately, this is in a protected variable.

I'm doing this as a one time operation, which I will be caching, and it doesn't take too long, so I decided I could afford to parse the layouts again.

There is a handy public function to do this. It's Mage_Core_Model_Layout_Update::getFileLayoutUpdatesXml($area, $package, $theme, $storeId).

I called it the same way they call it in fetchFileLayoutUpdates (which saves its xml in the aforementioned protected variable):

$update = Mage::app()->getLayout()->getUpdate();
$design = Mage::getSingleton('core/design_package');
$layout = $update->getFileLayoutUpdatesXml(
    $design->getArea(),
    $design->getPackageName(),
    $design->getTheme('layout'),
    Mage::app()->getStore()->getId()
);

This is the full xml layout tree, which is useful for a lot of things. My module defines a block called amdjs_modules, and I wanted to know the layout handle where a method was called inside this block. Well, this requires two different XPath queries, unless somebody who learned XPath earlier than yesterday can tell me a better way.

$modules = $layout->xpath("//block[@name=\"amdjs_modules\"]/action/*|//reference[@name=\"amdjs_modules\"]/action/*");

This gives an array of each argument given to every action in my block, referred to by the block name, or the reference.

Once you have these, mapping them to their handle is easy:

$handleMap = array();
foreach ($els as $el) {
    $handleMap[$el->__toString()] = $el->xpath("ancestor::*[parent::layouts]")[0]->getName();
}

This works on the assumption that each handle is directly below the root node.