Zend framework 2: Invalid instantiator of type "NULL" for "Zend\Form\FormInterface" - zend-form

Question

I am not able to instantiate my forms via DI due to strange exception.
Here is the code snippet to reproduce exception I got
include 'Zend/Loader/AutoloaderFactory.php';
Zend\Loader\AutoloaderFactory::factory(array(
'Zend\Loader\StandardAutoloader' => array(
'autoregister_zf' => true
)
));
include 'Zend/Di/Di.php';
$di = new Zend\Di\Di();
$form = $di->get('Zend\Form\Form');
I always get
Fatal error: Uncaught exception 'Zend\Di\Exception\RuntimeException' with message 'Invalid instantiator of type "NULL" for "Zend\Form\FormInterface".'
What am I doing wrong? Any help and/or suggestions are greatly appreciated.

Answer 1

I digged into this and indeed an exception is thrown. Try running following:
$def = new \Zend\Di\Definition\RuntimeDefinition();
var_dump($def->getMethods('Zend\Form\Form'));
This will dump all methods that Zend\Di will understand as "injection methods". The output will be something like
array (size=23)
'__construct' => boolean true
'setData' => boolean false
'setHydrator' => boolean false
'setBindOnValidate' => boolean false
'setBaseFieldset' => boolean false
'setValidationGroup' => boolean false
'setInputFilter' => boolean false
'setUseInputFilterDefaults' => boolean false
'setPreferFormInputFilter' => boolean false
'setWrapElements' => boolean false
'setOptions' => boolean false
'setFormFactory' => boolean true
'setPriority' => boolean false
'setMessages' => boolean false
'setObject' => boolean false
'setUseAsBaseFieldset' => boolean false
'setName' => boolean false
'setAttribute' => boolean false
'setAttributes' => boolean false
'setValue' => boolean false
'setLabel' => boolean false
'setLabelAttributes' => boolean false
'prepareElement' => boolean true
As you can see, method prepareElement(FormInterface $form) is marked as injection method. That is because (as of current Di introspection strategy) prepareElement is defined in interface Zend\Form\ElementPrepareAwareInterface, and that since 2.1.0.
Since injection methods are marked to be called by Zend\Di after the object is instantiated, Zend\Di is hereby failing to find an instance for Zend\Form\FormInterface (which isn't Zend\Form\Form).
So as you can see the change has nothing to do with Zend\Di in this case. You could eventually report it or alter the introspection strategy to suit your needs.
I personally don't think Zend\Di should call that method, nor that the method should be part of an *Aware* interface.