Fluid array, if all elements are deleted the array is not empty, but a string - typo3

Question

When I have an array in flux:
<flux:form.section name="links" label="Links">
<flux:form.object name="link" label="Link">
<flux:field.input name="linktext" label="Linktext"/>
</flux:form.object>
</flux:form.section>
I first check if the array is set before I render it with fluid:
<f:if condition="{links}">
<ul class="menulinks">
<f:for each="{links}" as="linkelement">
<li>{linkelement.link.linktext}</li>
</f:for>
</ul>
</f:if>
This works. But if there were items set but then deleted, {links} is not empty. It is set as a string with a whitespace " ". And that means the condition in the if-Tag returns true.
And this can lead to an error. In this case I had an error in the backend, but not on the frontend. Even I used nearly the same code in <f:section name="Preview"> and <f:section name="Main">.
My idea was to check the type of {links} and only return true if the type is array. But I am not sure if this is possible with fluid. What other options I have?
The errorreport I see in the backend:
The argument "each" was registered with type "array", but is of type "string" in view helper "TYPO3\CMS\Fluid\ViewHelpers\ForViewHelper"

Answer 1

My idea was to check the type of {links} and only return true if the type is array. But I am not sure if this is possible with fluid.
It is. You can always implement your own ViewHelper if you need support for something, fluid does not bring out of the box. To add the ViewHelper you need, create a php file called IfIsNonEmptyArrayViewHelper.php in some_extension/Classes/ViewHelpers/. The implementation is quite easy:
<?php
namespace Vendor\SomeExtension\ViewHelpers;
class IfIsNonEmptyArrayViewHelper extends \TYPO3\CMS\Fluid\Core\ViewHelper\AbstractConditionViewHelper {
/**
* #param mixed $variable
* #return string
*/
public function render($variable) {
if (is_array($variable) && !empty($variable)) {
return $this->renderThenChild();
}
return $this->renderElseChild();
}
}
After that you only have to add your own fluid namespace to your template like this: {namespace ns=Vendor\SomeExtension\ViewHelpers}
Now you can write your condition like this:
<ns:ifIsNonEmptyArray variable="{links}">
<ul class="menulinks">
<f:for each="{links}" as="linkelement">
<li>{linkelement.link.linktext}</li>
</f:for>
</ul>
</ns:ifIsNonEmptyArray>
Of course ns, Vendor and SomeExtension are just placeholders for the real names.