PHP5

Let's use a registration form as an example. For our purposes, we want to capture the desired username and password on the first page, then the user's metadata -- given name, family name, and location -- and finally allow them to decide what mailing lists, if any, they wish to subscribe to.

First, let's create our own form, and define several sub forms within it:

<?php class My_Form_Registration extends Zend_Form
{
    public function init()
    {
        // Create user sub form: username and password
        $user = new Zend_Form_SubForm();
        $user->addElements(array(
            new Zend_Form_Element_Text('username', array(
                'required'   => true,
                'label'      => 'Username:',
                'filters'    => array('StringTrim', 'StringToLower'),
                'validators' => array(
                    'Alnum',
                    array('Regex', false, array('/^[a-z][a-z0-9]{2,}$/'))
                )
            )),

            new Zend_Form_Element_Password('password', array(
                'required'   => true,
                'label'      => 'Password:',
                'filters'    => array('StringTrim'),
                'validators' => array(
                    'NotEmpty',
                    array('StringLength', false, array(6))
                )
            )),
        ));

        // Create demographics sub form: given name, family name, and location
        $demog = new Zend_Form_SubForm();
        $demog->addElements(array(
            new Zend_Form_Element_Text('givenName', array(
                'required'   => true,
                'label'      => 'Given (First) Name:',
                'filters'    => array('StringTrim'),
                'validators' => array(
                    array('Regex', false, array('/^[a-z][a-z0-9., \'-]{2,}$/i'))
                )
            )),

            new Zend_Form_Element_Text('familyName', array(
                'required'   => true,
                'label'      => 'Family (Last) Name:',
                'filters'    => array('StringTrim'),
                'validators' => array(
                    array('Regex', false, array('/^[a-z][a-z0-9., \'-]{2,}$/i'))
                )
            )),

            new Zend_Form_Element_Text('location', array(
                'required'   => true,
                'label'      => 'Your Location:',
                'filters'    => array('StringTrim'),
                'validators' => array(
                    array('StringLength', false, array(2))
                )
            )),
        ));

        // Create mailing lists sub form
        $listOptions = array(
            'none'        => 'No lists, please',
            'fw-general'  =>  'Zend Framework General List',
            'fw-mvc'      =>  'Zend Framework MVC List',
            'fw-auth'     =>  'Zend Framwork Authentication and ACL List',
            'fw-services' => 'Zend Framework Web Services List',
        );
        $lists = new Zend_Form_SubForm();
        $lists->addElements(array(
            new Zend_Form_Element_MultiCheckbox('subscriptions', array(
                'label'        => 'Which lists would you like to subscribe to?',
                'multiOptions' => $listOptions,
                'required'     => true,
                'filters'      => array('StringTrim'),
                'validators'   => array(
                    array('InArray', false, array(array_keys($listOptions)))
                )
            )),
        ));

        // Attach sub forms to main form
        $this->addSubForms(array(
            'user'  => $user,
            'demog' => $demog,
            'lists' => $lists
        ));
    }
}

Note that there are no submit buttons, and that we have done nothing with the sub form decorators -- which means that by default they will be displayed as fieldsets. We will need to be able to override these as we display each individual sub form, and add in submit buttons so we can actually process them -- which will also require action and method properties. Let's add some scaffolding to our class to provide that information:

 class My_Form_Registration extends Zend_Form
{
    // ...

    /**
     * Prepare a sub form for display
     * 
     * @param  string|Zend_Form_SubForm $spec 
     * @return Zend_Form_SubForm
     */
    public function prepareSubForm($spec)
    {
        if (is_string($spec)) {
            $subForm = $this->{$spec};
        } elseif ($spec instanceof Zend_Form_SubForm) {
            $subForm = $spec;
        } else {
            throw new Exception('Invalid argument passed to ' . __FUNCTION__ . '()');
        }
        $this->setSubFormDecorators($subForm)
             ->addSubmitButton($subForm)
             ->addSubFormActions($subForm);
        return $subForm;
    }

    /**
     * Add form decorators to an individual sub form
     * 
     * @param  Zend_Form_SubForm $subForm
     * @return My_Form_Registration
     */
    public function setSubFormDecorators(Zend_Form_SubForm $subForm)
    {
        $subForm->setDecorators(array(
            'FormElements',
            array('HtmlTag', array('tag' => 'dl', 'class' => 'zend_form')),
            'Form',
        ));
        return $this;
    }

    /**
     * Add a submit button to an individual sub form
     * 
     * @param  Zend_Form_SubForm $subForm
     * @return My_Form_Registration
     */
    public function addSubmitButton(Zend_Form_SubForm $subForm)
    {
        $subForm->addElement(new Zend_Form_Element_Submit(
            'save', 
            array(
                'label'    => 'Save and continue',
                'required' => false,
                'ignore'   => true,
            )
        ));
        return $this;
    }

    /**
     * Add action and method to sub form
     * 
     * @param  Zend_Form_SubForm $subForm 
     * @return My_Form_Registration
     */
    public function addSubFormActions(Zend_Form_SubForm $subForm)
    {
        $subForm->setAction('/registration/process')
                ->setMethod('post');
        return $this;
    }
}

Next, we need to add some scaffolding in our action controller, and have several considerations. First, we need to make sure we persist form data between requests, so that we can determine when to quit. Second, we need some logic to determine what form segments have already been submitted, and what sub form to display based on that information. We'll use Zend_Session_Namespace to persist data, which will also help us answer the question of which form to submit.

Let's create our controller, and add a method for retrieving a form instance:

<?php class RegistrationController extends Zend_Controller_Action
{
    protected $_form;

    public function getForm()
    {
        if (null === $this->_form) {
            require_once 'My/Form/Registration.php';
            $this->_form = new My_Form_Registration();
        }
        return $this->_form;
    }
}

Now, let's add some functionality for determining which form to display. Basically, until the entire form is considered valid, we need to continue displaying form segments. Additionally, we likely want to make sure they're in a particular order: user, demog, and then lists. We can determine what data has been submitted by checking our session namespace for particular keys representing each subform.

 class RegistrationController extends Zend_Controller_Action
{
    // ...

    protected $_namespace = 'RegistrationController';
    protected $_session;

    /**
     * Get the session namespace we're using
     * 
     * @return Zend_Session_Namespace
     */
    public function getSessionNamespace()
    {
        if (null === $this->_session) {
            require_once 'Zend/Session/Namespace.php';
            $this->_session = new Zend_Session_Namespace($this->_namespace);
        }

        return $this->_session;
    }

    /**
     * Get a list of forms already stored in the session
     * 
     * @return array
     */
    public function getStoredForms()
    {
        $stored = array();
        foreach ($this->getSessionNamespace() as $key => $value) {
            $stored[] = $key;
        }

        return $stored;
    }

    /**
     * Get list of all subforms available
     * 
     * @return array
     */
    public function getPotentialForms()
    {
        return array_keys($this->getForm()->getSubForms());
    }

    /**
     * What sub form was submitted?
     * 
     * @return false|Zend_Form_SubForm
     */
    public function getCurrentSubForm()
    {
        $request = $this->getRequest();
        if (!$request->isPost()) {
            return false;
        }

        foreach ($this->getPotentialForms() as $name) {
            if ($data = $request->getPost($name, false)) {
                if (is_array($data)) {
                    return $this->getForm()->getSubForm($name);
                    break;
                }
            }
        }

        return false;
    }

    /**
     * Get the next sub form to display
     * 
     * @return Zend_Form_SubForm|false
     */
    public function getNextSubForm()
    {
        $storedForms    = $this->getStoredForms();
        $potentialForms = $this->getPotentialForms();

        foreach ($potentialForms as $name) {
            if (!in_array($name, $storedForms)) {
                return $this->getForm()->getSubForm($name);
            }
        }

        return false;
    }
}

The above methods allow us to use notations such as "$subForm = $this->getCurrentSubForm();" to retrieve the current sub form for validation, or "$next = $this->getNextSubForm();" to get the next one to display.

Now, let's figure out how to process and display the various sub forms. We can use getCurrentSubForm() to determine if any sub forms have been submitted (false return values indicate none have been displayed or submitted), and getNextSubForm() to retrieve a form to display. We can then use the form's prepareSubForm() method to ensure the form is ready for display.

When we have a form submission, we can validate the sub form, and then check to see if the entire form is now valid. To do these tasks, we'll need additional methods that ensure that submitted data is added to the session, and that when validating the form entire, we validate against all segments from the session:

<?php class My_Form_Registration extends Zend_Form
{
    // ...
    
    /**
     * Is the sub form valid?
     * 
     * @param  Zend_Form_SubForm $subForm 
     * @param  array $data 
     * @return bool
     */
    public function subFormIsValid(Zend_Form_SubForm $subForm, array $data)
    {
        $name = $subForm->getName();
        if ($subForm->isValid($data)) {
            $this->getSessionNamespace()->$name = $subForm->getValues();
            return true;
        }

        return false;
    }

    /**
     * Is the full form valid?
     * 
     * @return bool
     */
    public function formIsValid()
    {
        $data = array();
        foreach ($this->getSessionNamespace() as $key => $info) {
            $data[$key] = $info;
        }

        return $this->getForm()->isValid($data);
    }
}

Now that we have the legwork out of the way, let's build the actions for this controller. We'll need a landing page for the form, and then a 'process' action for processing the form.

<?php class My_Form_Registration extends Zend_Form
{
    // ...

    public function indexAction()
    {
        // Either re-display the current page, or grab the "next" (first) 
        // sub form
        if (!$form = $this->getCurrentSubForm()) {
            $form = $this->getNextSubForm();
        }
        $this->view->form = $this->getForm()->prepareSubForm($form);
    }

    public function processAction()
    {
        if (!$form = $this->getCurrentSubForm()) {
            return $this->_forward('index');
        }

        if (!$this->subFormIsValid($form, $this->getRequest()->getPost())) {
            $this->view->form = $this->getForm()->prepareSubForm($form);
            return $this->render('index');
        }

        if (!$this->formIsValid()) {
            $form = $this->getNextSubForm();
            $this->view->form = $this->getForm()->prepareSubForm($form);
            return $this->render('index');
        }

        // Valid form!
        // Render information in a verification page
        $this->view->info = $this->getSessionNamespace();
        $this->render('verification');
    }
}

As you'll notice, the actual code for processing the form is relatively simple. We check to see if we have a current sub form submission, and if not, we go back to the landing page. If we do have a sub form, we attempt to validate it, redisplaying it if it fails. If the sub form is valid, we then check to see if the form is valid, which would indicate we're done; if not, we display the next form segment. Finally, we display a verification page with the contents of the session.

The view scripts are very simple:

<? // registration/index.phtml ?>
<h2>Registration</h2>
<?= $this->form ?>

<? // registration/verification.phtml ?>
<h2>Thank you for registering!</h2>
<p>
    Here is the information you provided:
</p>

<?
// Have to do this construct due to how items are stored in session namespaces
foreach ($this->info as $info):
    foreach ($info as $form => $data): ?>
<h4><?= ucfirst($form) ?>:</h4>
<dl>
    <? foreach ($data as $key => $value): ?>
    <dt><?= ucfirst($key) ?></dt>
    <? if (is_array($value)):
        foreach ($value as $label => $val): ?>
    <dd><?= $val ?></dd>
        <? endforeach;
       else: ?>
    <dd><?= $this->escape($value) ?></dd>
    <? endif;
    endforeach; ?>
</dl>
<? endforeach;
endforeach ?>

Upcoming releases of Zend Framework will include components to make multi page forms simpler by abstracting the session and ordering logic. In the meantime, the above example should serve as a reasonable guideline on how to accomplish this task for your site.