Magento layout: block groups

Something I recently found out, is a feature that all blocks have. Interestingly enough, it wasn’t part of the Frontend certification, maybe because it isn’t used very much. I decided to dig into it anyway.

It’s pretty simple - Mage_Core_Block_Abstract has the ability to group it’s children blocks without the need to use text lists.

The blockgroup API

The API looks something like this:

addToChildGroup($groupname, Mage_Core_Block_Abstract $child)

Unfortunately, you cannot call this function in layout XML because you can’t pass a block to a method - the XML parser doesn’t work that way. That means you can only create a group programmatically by using this method. But fear not, check out the next method and its implementation:

public function addToParentGroup($groupName)
{
    $this->getParentBlock()->addToChildGroup($groupName, $this);
    return $this;
}

This adds the block that’s executing the method to it’s parent block group.

Next up:

getChildGroup($groupName, $callback = null, $skipEmptyResults = true)

Documentation states:

 * Get a group of child blocks
 *
 * Returns an array of <alias> => <block>
 * or an array of <alias> => <callback_result>
 * The callback currently supports only $this methods and passes the alias as parameter

That means you can render a group with the following code (stolen from catalog/product/view.phtml):

foreach ($this->getChildGroup('detailed_info', 'getChildHtml') as $alias => $html) {
    echo $html;
}

It’s interesting that you can pass a callback to getChildGroup - the first time I see something like this in Magento. This means you can do something like:

$group = getChildGroup('detailed_info', getCacheLifetime)

...and get all cache lifetimes. I’m not quite sure why you would ever want to pass something other than getChildHtml, but it’s possible.

Why use this over text list blocks?

By using a group, we don’t need to use a text_list anymore and can keep our block hierarchy simpler:

block
    block-1-1
    block-1-2

    block-2-1
    block-2-2

block
    text-list
        block-1-1
        block-1-2
    text-list
        block-2-1
        block-2-2

What about Magento 2?

As far as I can see, Magento 2 doesn't have this feature. However, with the current state that Magento 2 is at, there is plenty of time for the codepool to change.

blocks layout.xml magento