ZF2 FormInput to show error class on validation fail - zend-framework2

Question

My form has multiple elements being rendered in the format:
<div class="form-group">
<?php echo $this->formlabel($form->get('lastname')); ?>
<?php echo $this->forminput($form->get('lastname')); ?>
<?php echo $this->formElementErrors($form->get('lastname')); ?>
</div>
I do this so I can have my element next to my label as opposed to inside it:
<label for="lastname">Lastname</label><input .../>
<ul><li>error messages</li></ul>
What I have noticed is that on validation fail the input is not getting the input-error class. When I change the above code to <?php echo $this->formrow($form->get('lastname')); ?> the input is put into the label (which I don't want) and the input gets the error class as expected:
<label>Lastname<input ... class="input-error"/></label>
How do I get the input-error class into the element via $this->forminput?
When I do formrow before forminput then the input in both has the error class, but when I do forminput on it's own it does not.
[edit]
Short term I have put formrow (without the echo) above my existing code and now my input field is showing the error class, but that feels like a bit of a hack, and I would have to do that for each element in my app that I have set up like this.

Answer 1

I have created a view helper to add the missing class to forminput:
<?php
/**
* Extend zend form view helper forminput to add error class to element on validation
* fail
*
* #package RPK
* #author Richard Parnaby-King
*/
namespace RPK\Form\View\Helper;
use Zend\Form\View\Helper\FormInput as ZendFormInput;
class FormInput extends ZendFormInput
{
protected $inputErrorClass = 'input-error';
/**
* Render a form <input> element from the provided $element
*
* #param ElementInterface $element
* #throws Exception\DomainException
* #return string
*/
public function render(\Zend\Form\ElementInterface $element)
{
$inputErrorClass = $this->inputErrorClass;
// Following code block copied from \Zend\Form\View\Helper\FormRow
// Does this element have errors ?
if (count($element->getMessages()) > 0 && !empty($inputErrorClass)) {
$classAttributes = ($element->hasAttribute('class') ? $element->getAttribute('class') . ' ' : '');
$classAttributes = $classAttributes . $inputErrorClass;
$element->setAttribute('class', $classAttributes);
}
return parent::render($element);
}
}
I then tell my application to use this view helper in my Module.php file:
public function onBootstrap(MvcEvent $e) {
$services = $e->getApplication()->getServiceManager();
//add custom forminput viewhelper
$services->get('ViewHelperManager')->setFactory('forminput', function (\Zend\View\HelperPluginManager $manager) {
return new \RPK\Form\View\Helper\FormInput();
});
}