XML syntax to change block's template

[cescopag]

Summary

Documentation claims that it is possible to change a block's template by the following layout update:

<referenceBlock name="navigation.sections">
  <arguments>
    <argument name="template" xsi:type="string">Magento_Theme::html/nav_sections.phtml</argument>
  </arguments>
</referenceBlock>

But It doesn't work.

Using action node, instead of arguments node, works fine:

<referenceBlock name="navigation.sections">
  <action method="setTemplate">
    <argument name="template" xsi:type="string">Magento_Theme::html/nav_sections.phtml</argument>
  </action>
</referenceBlock>

Source:
http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/layouts/xml-manage.html#set_template

Preconditions (*)

1. Magento 2.3-develop
2. PHP 7.2

Steps to reproduce (*)

Try to change a block's template by the following layout update
e.g.:

Expected result (*)

Block's template is changed without any errors

Actual result (*)

Got exception

[shiftedreality]

Hi @cescopag

You provided correct way with action method
Looks like mistake in public docs

[almarchenko]

Hi @cescopag!
Thank you for reporting this. Looks like there's a bug in magento code, that is why the code sample provided in docs doesn't work. But you found the correct temporary solution.
It must be temporarily as is deprecated. I'll add a note in docs, and updated them when the bug is fixed.

[LiamFielding]

Is this now fixed?

[dnadle]

In 2.1.0 I still have to use 'action' and the online documentation is still wrong.

[LiamFielding]

@digitalpianism No, sorry - I believe that's what we all tried first. At least I did, that's how I ended up here.

[digitalpianism]

@LiamFielding my bad. I guess we gotta wait ^^

[sylvainraye]

The reason why it doesn't work is because the method \Magento\Framework\View\Layout\Generator\Block::generateBlock:

When we want to overwrite an existing block, this one was at first initialized via a layout XML with an attribute template.

Into the generateBlockmethod, arguments are passed to the block, then setTemplate is called and then in the calling method process the action is called.

So the priority is the following:

• actions
• setTemplate via attribute template
• arguments

When a block was initialized with its attribute template, arguments will have no effect. That's why you need to use actions

protected function generateBlock(
        Layout\ScheduledStructure $scheduledStructure,
        Layout\Data\Structure $structure,
        $elementName
    ) {
        list(, $data) = $scheduledStructure->getElement($elementName);
        $attributes = $data['attributes'];

        if (!empty($attributes['group'])) {
            $structure->addToParentGroup($elementName, $attributes['group']);
        }
        if (!empty($attributes['display'])) {
            $structure->setAttribute($elementName, 'display', $attributes['display']);
        }

        // create block
        $className = $attributes['class'];
        $block = $this->createBlock($className, $elementName, [
            'data' => $this->evaluateArguments($data['arguments'])
        ]);
        if (!empty($attributes['template'])) {
            $block->setTemplate($attributes['template']);
        }
        if (!empty($attributes['ttl'])) {
            $ttl = (int)$attributes['ttl'];
            $block->setTtl($ttl);
        }
        return $block;
    }

[nsergo]

Issue in progress @nsergo & @sambolek