What is the difference between render() and renderStatic() and what should be used when writing a ViewHelper in TYPO3

Question

There are several examples for writing a custom ViewHelper and different ways to do things. I have seen examples with render() and with renderStatic (for example in Developing a Custom ViewHelper).

In 24 Fluid Tips there is an explanation, but I don't understand it and it does not make it clear for me why there are 2 functions and what should be used where.

Breaking changes (Render method arguments on ViewHelpers deprecated) and fragmented information in various places makes it difficult to get a clear answer here. Is the example in Developing a Custom ViewHelper up to date and best practice?

Mezzotint

Answer 1

▸ renderStatic()
First of all, renderStatic() is a static PHP method. This means, you do not have access to instance attributes, such as $this->tag, which is for example required when your ViewHelper class is a subclass of AbstractTagBasedViewHelper.

Another drawback of renderStatic() is that you can not access child nodes. A child node is for example <f:then> in the following example:

<f:if condition="{variable}">
<f:then>
...
</f:then>
</f:if>

Having said that, renderStatic() features the best performance, because it is called from within compiled Fluid. Therefore, this method should be used if possible.

▸ render()
Under certain circumstances, this method is the better choice or has to be used for a specific use case (see explanations above). The logic implemented in a render() method is not compiled, which has an impact on output that is cached.

The downside of render() is its performance.

▸ Summary / Additional Notes

• Use renderStatic(), if you can (performance).
• Use render(), if you implement an TagBased-ViewHelper (subclass of
  TYPO3Fluid\Fluid\Core\ViewHelper\AbstractTagBasedViewHelper).
• Use render(), if you need to read child nodes.
• Review the ViewHelpers that are shipped with Fluid (e.g. TYPO3 v9 LTS) as examples.
  (see: typo3/sysext/fluid/Classes/ViewHelpers/*) [GitHub]

Paragraphia

This is a brilliant answer! Thanks. – Mezzotint

@Michael, Nice to have you on stackoverflow, Hope you remember. – Collettecolletti