Advanced use cases

Beginning with version 2.1, forms elements can be registered using a designated plugin manager, in the same way that view helpers, controller plugins, and filters are registered. This new feature has a number of benefits, especially when you need to handle complex dependencies in forms/fieldsets.

Short names

The first advantage of pulling form elements from the service manager is that now you can use short names to create new elements through the factory. Therefore, this code:

$form->add([
    'type' => Element\Email::class,
    'name' => 'email',
]);

can now be replaced by:

$form->add([
     'type' => 'Email',
     'name' => 'email'
]);

Each element provided out-of-the-box by zend-form supports this natively.

Use the ::class constant

While using aliases leads to compact code, they're also can more easily result in typographic mistakes. We recommend using the ::class constant in most situations, as these can be more easily scanned with static analysis tools for correctness.

Creating custom elements

zend-form also supports custom form elements.

To create a custom form element, make it extend the Zend\Form\Element class, or, if you have a more specific dependency, extend one of the classes in the Zend\Form\Element namespace.

In the following, we will demonstrate creating a custom Phone element for entering phone numbers. It will extend Zend\Form\Element class and provide some default input rules.

Our custom phone element could look something like this:

namespace Application\Form\Element;

use Zend\Filter;
use Zend\Form\Element;
use Zend\InputFilter\InputProviderInterface;
use Zend\Validator\Regex as RegexValidator;

class Phone extends Element implements InputProviderInterface
{
    /**
     * @var ValidatorInterface
     */
    protected $validator;

    /**
    * Get a validator if none has been set.
    *
    * @return ValidatorInterface
    */
    public function getValidator()
    {
        if (null === $this->validator) {
            $validator = new RegexValidator('/^\+?\d{11,12}$/');
            $validator->setMessage(
                'Please enter 11 or 12 digits only!',
                RegexValidator::NOT_MATCH
            );

            $this->validator = $validator;
        }

        return $this->validator;
    }

    /**
     * Sets the validator to use for this element
     *
     * @param  ValidatorInterface $validator
     * @return self
     */
    public function setValidator(ValidatorInterface $validator)
    {
        $this->validator = $validator;
        return $this;
    }

    /**
     * Provide default input rules for this element
     *
     * Attaches a phone number validator.
     *
     * @return array
     */
    public function getInputSpecification()
    {
        return [
            'name' => $this->getName(),
            'required' => true,
            'filters' => [
                ['name' => Filter\StringTrim::class],
            ],
            'validators' => [
                $this->getValidator(),
            ],
        ];
    }
}

By implementing Zend\InputFilter\InputProviderInterface interface, we are hinting to our form object that this element provides some default input rules for filtering and/or validating values. In this example, the default input specification provides a Zend\Filter\StringTrim filter and a Zend\Validator\Regex validator that validates that the value optionally has a + sign at the beginning, and is followed by 11 or 12 digits.

To use the new element in our forms, we can specify it by its fully qualified class name (FQCN):

use Application\Form\Element\Phone;
use Zend\Form\Form;

$form = Form();
$form->add(array(
    'name' => 'phone',
    'type' => Phone::class,
));

Or, if you are extending Zend\Form\Form:

namespace Application\Form;

use Zend\Form\Form;

class MyForm extends Form
{
    public function __construct($name = null)
    {
        parent::__construct($name);

        $this->add([
            'name' => 'phone',
            'type' => Element\Phone::class,
        ]);
    }
}

If you don't want to use the custom element's FQCN, but rather a short name, add an entry for it to Zend\Form\FormElementManager. You can do this by adding an entry under the form_elements configuration, or within your Module class via a getFormElementConfig() method.

Configuration via a config file (e.g., module.config.php) file looks like the following:

use Zend\ServiceManager\Factory\InvokableFactory;

return [
    'form_elements' => [
        'aliases' => [
            'phone' => Application\Form\Element\Phone::class,
        ],
        'factories' => [
            Application\Form\Element\Phone::class => InvokableFactory::class,
        ],
    ],
];

The following demonstrates using your Module class:

namespace Application;

use Zend\ModuleManager\Feature\FormElementProviderInterface;
use Zend\ServiceManager\Factory\InvokableFactory;

class Module implements FormElementProviderInterface
{
    public function getFormElementConfig()
    {
        return [
            'aliases' => [
                'phone' => Form\Element\Phone::class,
            ],
            'factories' => [
                Form\Element\Phone::class => InvokableFactory::class,
            ],
        ];
    }
}

If needed, you can define a custom factory for handling dependencies.

And now comes the first catch.

If you are creating your form class by extending Zend\Form\Form, you must not add the custom element in the constructor (as we have done in the previous example where we used the custom element's FQCN), but rather in the init() method:

namespace Application\Form;

use Zend\Form\Form;

class MyForm extends Form
{
    public function init()
    {
        $this->add([
            'name' => 'phone',
            'type' => 'phone',
        ]);
    }
}

The second catch is that you must not directly instantiate your form class, but rather get an instance of it through Zend\Form\FormElementManager:

namespace Application\Controller;

use Application\Form\MyForm;
use Zend\Mvc\Controller\AbstractActionController;

class IndexController extends AbstractActionController
{
    private $form;

    public function __construct(MyForm $form)
    {
        $this->form = $form;
    }

    public function indexAction()
    {
        return array('form' => $this->form);
    }
}

This now requires a factory to inject the form instance:

namespace Application\Controller;

use Interop\Container\ContainerInterface;
use Application\Form\MyForm;

class IndexControllerFactory
{
    public function __invoke(ContainerInterface $container)
    {
        $formManager = $container->get('FormElementManager');
        return new IndexController($formManager->get(MyForm::class));
    }
}

Which in turn requires that you map the controller to the factory:

// In module.config.php
return [
    /* ... */
    'controllers' => [
        'factories' => [
            Application\Controller\IndexController::class => Application\Controller\IndexControllerFactory::class,
        ],
    ],
];

The biggest gain of this is that you can easily override any built-in form elements if they do not fit your needs. For instance, if you want to create your own Email element instead of the standard one, create your custom element, and add it to the form element config with the same key as the element you want to replace:

namespace Application;

use Zend\Form\Element\Email;
use Zend\ModuleManager\Feature\FormElementProviderInterface;
use Zend\ServiceManager\Factory\InvokableFactory;

class Module implements FormElementProviderInterface
{
    public function getFormElementConfig()
    {
        return [
            'aliases' => [
                'email' => Form\Element\MyEmail::class,
                'Email' => Form\Element\MyEmail::class,
            ],
            'factories' => [
                Form\Element\MyEmail::class => InvokableFactory::class,
            ],
        ];
    }
}

Now whenever you create an element with a type of 'email', it will create the custom element instead of the built-in one.

Use the original?

If you want to be able to use both the built-in one and your own one, you can still provide the FQCN of the element, e.g. Zend\Form\Element\Email.

In summary, to create your own form elements (or even reusable fieldsets!) and be able to use them in your form, you need to:

  1. Create your element (like you did before).
  2. Add it to the form element manager either via the form_elements configuration in your module, or by defining a getFormElementConfig() in your Module class.
  3. Make sure the custom form element is not added in the form's constructor, but rather in its init() method, or after getting an instance of the form.
  4. Retrieve your form through the form element manager instead of directly instantiating it, and inject it in your controller.

Handling dependencies

Dependency management can be complex. For instance, a very frequent use case is a form that creates a fieldset, but itself need access to the database to populate a Select element. Retrieving forms from the FormElementManager solves this issue, as factories it invokes have access to the application service container, and can use it to provide dependencies.

For instance, let's say that a form create a fieldset called AlbumFieldset:

namespace Application\Form;

use Zend\Form\Form;

class CreateAlbum extends Form
{
    public function init()
    {
        $this->add([
            'name' => 'album',
            'type' => AlbumFieldset::class,
        ]);
    }
}

Let's now create the AlbumFieldset, and have it depend on an AlbumTable object that allows us to fetch albums from the database.

namespace Application\Form;

use Album\Model\AlbumTable;
use Zend\Form\Fieldset;

class AlbumFieldset extends Fieldset
{
    public function __construct(AlbumTable $albumTable)
    {           
        // Add any elements that need to fetch data from database
        // using the album table !
    }
}

To enable this, we'll create a factory for our AlbumFieldset as follows:

namespace Application\Form;

use Album\Model\AlbumTable;
use Interop\Container\ContainerInterface;
use Zend\ServiceManager\FactoryInterface;
use Zend\ServiceManager\ServiceLocatorInterface;

class AlbumFieldsetFactory implements FactoryInterface
{
    public function __invoke(ContainerInterface $container, $name, array $options = null)
    {
        return new AlbumFieldset($container->get(AlbumTable::class));
    }

    public function createService(ServiceLocatorInterface $formManager)
    {
        return $this(
            $formManager->getServiceLocator() ?: $formManager,
            AlbumFieldset::class
        );
    }
}

Compatibility

The above factory was written to work with both the v2 and v3 releases of zend-servicemanager. If you know you will only be using v3, you can remove the createService() implementation.

You can now map the fieldset to the factory in your configuration:

// In module.config.php:
return [
    'form_elements' => [
        'factories' => [
            Application\Form\AlbumFieldset::class => Application\Form\AlbumFieldsetFactory::class,
        ],
    ],
];

Inject your form into your controller, per the example in the previous section.

As a reminder, to use your fieldset in a view, you need to use the formCollection helper:

echo $this->form()->openTag($form);
echo $this->formCollection($form->get('album'));
echo $this->form()->closeTag();

Initialization

As noted in previous sections, and in the chapter on elements, we recommend defining an init() method for initializing your elements, fieldsets, and forms. Where does this come from, and when exactly is it invoked in the object lifecycle?

The method is defined in Zend\Stdlib\InitializableInterface, which Zend\Form\Element implements. It is not, however, automatically invoked on instantiation!

Within zend-form, the FormElementManager defines an initializer that is pushed to the bottom of the initializer stack, making it the last initializer invoked. This initializer checks if the instance created implements InitializableInterface, and, if so, calls its init() method.

This approach ensures that dependencies are fully injected prior to any methods you call from your init() method. As a result, when pulling items from the FormElementManager, you can be assured that all factories are correctly setup and populated, and shared across all specifications you provide.