How Can A Block Render Without Specifying `as` property of the block, When we use getChildHtml() Method

Question

This is the source for my doubt. Please have a a look on this question, answer and answer's comment.

Basically the question demands to include a core/template block inside header block. For this we can use this code in layout XML.

<reference name="header">
    <block type="core/template" name="test_name" as="test_as" template="test/test.phtml" />
</reference>

and the test.phtml look like this.

<p><?php echo $this->__('Can you see me ?'); ?></p>

In order to see the content of my template, I need to call my test block inside header block as like this. This is because, header block is of type page/html_header and the block will not automatically convert its content to html as other core block does. So this is how we can call test block in header block.

<div><?php echo $this->getChildHtml('test_as') ?></div>

Note that, I am using the as property of test block to invoke that block in header block. Upto this everything is clear for me. But the actual doubt starts here.

Doubt :- If I didn't specify the as property in my test block and if I call my test block and then invokes the block as like this,

 <div><?php echo $this->getChildHtml('test_name'); ?></div>

it works and show the content of test.phtml in frontend. This also works.

 <div><?php echo $this->getChildHtml(); ?></div>

How it is possible to show the block output, by invoking that block with its name in its parent block ????

I am asking this because, there were lot of occasions in which I didn't specify as property that leaves a block not rendered. (even if I use name property of my block)

I know, magic happens here. But I can't just understand what exactly happens here.

public function getChildHtml($name = '', $useCache = true, $sorted = false)
{
    if ($name === '') {
        if ($sorted) {
            $children = array();
            foreach ($this->getSortedChildren() as $childName) {
                $children[$childName] = $this->getLayout()->getBlock($childName);
            }
        } else {
            $children = $this->getChild();
        }
        $out = '';
        foreach ($children as $child) {
            $out .= $this->_getChildHtml($child->getBlockAlias(), $useCache);
        }
        return $out;
    } else {
        return $this->_getChildHtml($name, $useCache);
    }
}

So any help mostly appreciated .

Thanks in Advance

Answer 1

The magic actually happens in Mage_Core_Block_Abstract::insert():

public function insert($block, $siblingName = '', $after = false, $alias = '')
{

    //...

    if ($block->getIsAnonymous()) {
        $this->setChild('', $block);
        $name = $block->getNameInLayout();
    } elseif ('' != $alias) {
        $this->setChild($alias, $block);
        $name = $block->getNameInLayout();
    } else {
        $name = $block->getNameInLayout();
        $this->setChild($name, $block);
    }

If there is no alias specified, the name is automatically used as alias.

Answer 2

When you don't pass anything to getChildHtml() the below part gets executed

  if ($name === '') {
        if ($sorted) {
            $children = array();
            foreach ($this->getSortedChildren() as $childName) {
                $children[$childName] = $this->getLayout()->getBlock($childName);
            }
        } else {
            $children = $this->getChild();
        }
        $out = '';
        foreach ($children as $child) {
            $out .= $this->_getChildHtml($child->getBlockAlias(), $useCache);
        }
        return $out;
    } 

This basically gets the list of children object either sorted or unsorted from either the layout object or Mage_Core_Block_Abstract::$_children

Whenever you do $this->loadLayout(); in a controller, it basically loads the blocks from xml handle and add the block objects to the layout model and subsequently the children blocks are also added to their parent's _children property. This happens in this function

Mage_Core_Block_Abstract::setChild($alias, $block)

{
        if (is_string($block)) {
            $block = $this->getLayout()->getBlock($block);
        }
        if (!$block) {
            return $this;
        }

        if ($block->getIsAnonymous()) {
            $suffix = $block->getAnonSuffix();
            if (empty($suffix)) {
                $suffix = 'child' . sizeof($this->_children);
            }
            $blockName = $this->getNameInLayout() . '.' . $suffix;

            if ($this->getLayout()) {
                $this->getLayout()->unsetBlock($block->getNameInLayout())
                    ->setBlock($blockName, $block);
            }

            $block->setNameInLayout($blockName);
            $block->setIsAnonymous(false);

            if (empty($alias)) {
                $alias = $blockName;
            }
        }

        $block->setParentBlock($this);
        $block->setBlockAlias($alias);
        $this->_children[$alias] = $block;
        return $this;
    }

So this is how

$this->getChildHtml('<As attribute of block>')
and $this->getChildHtml(); // to retrieve all child block html

Work!

I am trying to get a block when it's name attribute is mentioned in the layout file but the as property is not. I am not able to retrieve the html for that block in Magento 1.9