Zend_Form makes use of Zend_Loader_PluginLoader to allow developers to specify the locations of alternate elements and decorators. Each has its own plugin loader associated with it, and general accessors are used to retrieve and modify each.

The following loader types are used with the various plugin loader methods: 'element' and 'decorator'. The type names are case insensitive.

The methods used to interact with plugin loaders are as follows:

Additionally, you can specify prefix paths for all elements and display groups created through a Zend_Form instance using the following methods:

Custom elements and decorators are an easy way to share functionality between forms and encapsulate custom functionality. See the Custom Label example in the elements documentation for an example of how custom elements can be used as replacements for standard classes.

Zend_Form provides several accessors for adding and removing form elements from a form. These can take element object instances or serve as factories for instantiating the element objects themselves.

The most basic method for adding an element is addElement(). This method can take either an object of type Zend_Form_Element (or of a class extending Zend_Form_Element), or arguments for building a new element -- including the element type, name, and any configuration options.

Some examples:

// Using an element instance:
$element = new Zend_Form_Element_Text('foo');
$form->addElement($element);

// Using a factory
//
// Creates an element of type Zend_Form_Element_Text with the
// name of 'foo':
$form->addElement('text', 'foo');

// Pass label option to the element:
$form->addElement('text', 'foo', array('label' => 'Foo:'));

Once an element has been added to the form, you can retrieve it by name. This can be done either by using the getElement() method or by using overloading to access the element as an object property:

// getElement():
$foo = $form->getElement('foo');

// As object property:
$foo = $form->foo;

Occasionally, you may want to create an element without attaching it to the form (for instance, if you wish to make use of the various plugin paths registered with the form, but wish to later attach the object to a sub form). The createElement() method allows you to do so:

// $username becomes a Zend_Form_Element_Text object:
$username = $form->createElement('text', 'username');

// Get all values:
$values = $form->getValues();

// Get only 'foo' element's value:
$value = $form->getValue('foo');

$form->setDefaults($data);
$form->populate($data);

$form->reset();

// Set global prefix path:
// Creates paths for prefixes My_Foo_Filter, My_Foo_Validate,
// and My_Foo_Decorator
$form->addElementPrefixPath('My_Foo', 'My/Foo/');

// Just filter paths:
$form->addElementPrefixPath('My_Foo_Filter',
                            'My/Foo/Filter',
                            'filter');

// Just validator paths:
$form->addElementPrefixPath('My_Foo_Validate',
                            'My/Foo/Validate',
                            'validate');

// Just decorator paths:
$form->addElementPrefixPath('My_Foo_Decorator',
                            'My/Foo/Decorator',
                            'decorator');

$form->setElementDecorators(array(
    'ViewHelper',
    'Label'
));

$form->setElementDecorators(
    array(
        'ViewHelper',
        'Label'
    ),
    array(
        'foo',
        'bar'
    )
);

$form->setElementDecorators(
    array(
        'ViewHelper',
        'Label'
    ),
    array(
        'foo',
        'bar'
    ),
    false
);

$form->setElementFilters(array('StringTrim'));

Display groups are a way to create virtual groupings of elements for display purposes. All elements remain accessible by name in the form, but when iterating over the form or rendering, any elements in a display group are rendered together. The most common use case for this is for grouping elements in fieldsets.

The base class for display groups is Zend_Form_DisplayGroup. While it can be instantiated directly, it is usually best to use Zend_Form's addDisplayGroup() method to do so. This method takes an array of element names as its first argument, and a name for the display group as its second argument. You may optionally pass in an array of options or a Zend_Config object as the third argument.

Assuming that the elements 'username' and 'password' are already set in the form, the following code would group these elements in a 'login' display group:

$form->addDisplayGroup(array('username', 'password'), 'login');

You can access display groups using the getDisplayGroup() method, or via overloading using the display group's name:

// Using getDisplayGroup():
$login = $form->getDisplayGroup('login');

// Using overloading:
$login = $form->login;

$form->addDisplayGroup(
    array('foo', 'bar'),
    'foobar',
    array('disableLoadDefaultDecorators' => true)
);

$form->addDisplayGroupPrefixPath('My_Foo_Decorator', 'My/Foo/Decorator');

$form->setDisplayGroupDecorators(array(
    'FormElements',
    'Fieldset'
));

// Use the 'My_DisplayGroup' class
$form->addDisplayGroup(
    array('username', 'password'),
    'user',
    array('displayGroupClass' => 'My_DisplayGroup')
);

// Use the 'My_DisplayGroup' class for all display groups:
$form->setDefaultDisplayGroupClass('My_DisplayGroup');

Sub forms serve several purposes:

A sub form may be a Zend_Form object, or, more typically, a Zend_Form_SubForm object. The latter contains decorators suitable for inclusion in a larger form (i.e., it does not render additional HTML form tags, but does group elements). To attach a sub form, simply add it to the form and give it a name:

$form->addSubForm($subForm, 'subform');

You can retrieve a sub form using either getSubForm($name) or overloading using the sub form name:

// Using getSubForm():
$subForm = $form->getSubForm('subform');

// Using overloading:
$subForm = $form->subform;

Sub forms are included in form iteration, although the elements they contain are not.

$form->setSubFormDecorators(array(
    'FormElements',
    'Fieldset'
));

While a form's usefulness primarily derives from the elements it contains, it can also contain other metadata, such as a name (often used as a unique ID in the HTML markup); the form action and method; the number of elements, groups, and sub forms it contains; and arbitrary metadata (usually used to set HTML attributes for the form tag itself).

You can set and retrieve a form's name using the name accessors:

// Set the name:
$form->setName('registration');

// Retrieve the name:
$name = $form->getName();

To set the action (url to which the form submits) and method (method by which it should submit, e.g., 'POST' or 'GET'), use the action and method accessors:

// Set the action and method:
$form->setAction('/user/login')
     ->setMethod('post');

You may also specify the form encoding type specifically using the enctype accessors. Zend_Form defines two constants, Zend_Form::ENCTYPE_URLENCODED and Zend_Form::ENCTYPE_MULTIPART, corresponding to the values 'application/x-www-form-urlencoded' and 'multipart/form-data', respectively; however, you can set this to any arbitrary encoding type.

// Set the action, method, and enctype:
$form->setAction('/user/login')
     ->setMethod('post')
     ->setEnctype(Zend_Form::ENCTYPE_MULTIPART);

Zend_Form implements the Countable interface, allowing you to pass it as an argument to count:

$numItems = count($form);

Setting arbitrary metadata is done through the attribs accessors. Since overloading in Zend_Form is used to access elements, display groups, and sub forms, this is the only method for accessing metadata.

// Setting attributes:
$form->setAttrib('class', 'zend-form')
     ->addAttribs(array(
         'id'       => 'registration',
         'onSubmit' => 'validate(this)',
     ));

// Retrieving attributes:
$class = $form->getAttrib('class');
$attribs = $form->getAttribs();

// Remove an attribute:
$form->removeAttrib('onSubmit');

// Clear all attributes:
$form->clearAttribs();

Creating the markup for a form is often a time-consuming task, particularly if you plan on re-using the same markup to show things such as validation errors, submitted values, etc. Zend_Form's answer to this issue is decorators.

Decorators for Zend_Form objects can be used to render a form. The FormElements decorator will iterate through all items in a form -- elements, display groups, and sub forms -- and render them, returning the result. Additional decorators may then be used to wrap this content, or append or prepend it.

The default decorators for Zend_Form are FormElements, HtmlTag (wraps in a definition list), and Form; the equivalent code for creating them is as follows:

$form->setDecorators(array(
    'FormElements',
    array('HtmlTag', array('tag' => 'dl')),
    'Form'
));

This creates output like the following:

<form action="/form/action" method="post">
<dl>
...
</dl>
</form>

Any attributes set on the form object will be used as HTML attributes of the <form> tag.

$form = new Zend_Form(array('disableLoadDefaultDecorators' => true));

// Alias to 'FooBar':
$form->addDecorator(array('FooBar' => 'HtmlTag'), array('tag' => 'div'));

// And retrieve later:
$form = $element->getDecorator('FooBar');

// Add two 'HtmlTag' decorators, aliasing one to 'FooBar':
$form->addDecorators(
    array('HtmlTag', array('tag' => 'div')),
    array(
        'decorator' => array('FooBar' => 'HtmlTag'),
        'options' => array('tag' => 'dd')
    ),
);

// And retrieve later:
$htmlTag = $form->getDecorator('HtmlTag');
$fooBar  = $form->getDecorator('FooBar');

You may create your own decorators for generating the form. One common use case is if you know the exact HTML you wish to use; your decorator could create the exact HTML and simply return it, potentially using the decorators from individual elements or display groups.

The following methods may be used to interact with decorators:

Zend_Form also uses overloading to allow rendering specific decorators. __call() will intercept methods that lead with the text 'render' and use the remainder of the method name to lookup a decorator; if found, it will then render that single decorator. Any arguments passed to the method call will be used as content to pass to the decorator's render() method. As an example:

// Render only the FormElements decorator:
echo $form->renderFormElements();

// Render only the fieldset decorator, passing in content:
echo $form->renderFieldset("<p>This is fieldset content</p>");

If the decorator does not exist, an exception is raised.

A primary use case for forms is validating submitted data. Zend_Form allows you to validate an entire form, a partial form, or responses for XmlHttpRequests (AJAX). If the submitted data is not valid, it has methods for retrieving the various error codes and messages for elements and sub forms.

To validate a full form, use the isValid() method:

if (!$form->isValid($_POST)) {
    // failed validation
}

isValid() will validate every required element, and any unrequired element contained in the submitted data.

Sometimes you may need to validate only a subset of the data; for this, use isValidPartial($data):

if (!$form->isValidPartial($data)) {
    // failed validation
}

isValidPartial() only attempts to validate those items in the data for which there are matching elements; if an element is not represented in the data, it is skipped.

When validating elements or groups of elements for an AJAX request, you will typically be validating a subset of the form, and want the response back in JSON. processAjax() does precisely that:

$json = $form->processAjax($data);

You can then simply send the JSON response to the client. If the form is valid, this will be a boolean TRUE response. If not, it will be a javascript object containing key/message pairs, where each 'message' is an array of validation error messages.

For forms that fail validation, you can retrieve both error codes and error messages, using getErrors() and getMessages(), respectively:

$codes = $form->getErrors();
$messages = $form->getMessages();

You can retrieve codes and error messages for individual elements by simply passing the element name to each:

$codes = $form->getErrors('username');
$messages = $form->getMessages('username');

$validValues = $form->getValidValues($_POST);

The following is a full list of methods available to Zend_Form, grouped by type:

Zend_Form is fully configurable via setOptions() and setConfig() (or by passing options or a Zend_Config object to the constructor). Using these methods, you can specify form elements, display groups, decorators, and metadata.

As a general rule, if 'set' + the option key refers to a Zend_Form method, then the value provided will be passed to that method. If the accessor does not exist, the key is assumed to reference an attribute, and will be passed to setAttrib().

Exceptions to the rule include the following:

As an example, here is a config file that passes configuration for every type of configurable data:

[element]
name = "registration"
action = "/user/register"
method = "post"
attribs.class = "zend_form"
attribs.onclick = "validate(this)"

disableTranslator = 0

prefixPath.element.prefix = "My_Element"
prefixPath.element.path = "My/Element/"
elementPrefixPath.validate.prefix = "My_Validate"
elementPrefixPath.validate.path = "My/Validate/"
displayGroupPrefixPath.prefix = "My_Group"
displayGroupPrefixPath.path = "My/Group/"

elements.username.type = "text"
elements.username.options.label = "Username"
elements.username.options.validators.alpha.validator = "Alpha"
elements.username.options.filters.lcase = "StringToLower"
; more elements, of course...

elementFilters.trim = "StringTrim"
;elementDecorators.trim = "StringTrim"

displayGroups.login.elements.username = "username"
displayGroups.login.elements.password = "password"
displayGroupDecorators.elements.decorator = "FormElements"
displayGroupDecorators.fieldset.decorator = "Fieldset"

decorators.elements.decorator = "FormElements"
decorators.fieldset.decorator = "FieldSet"
decorators.fieldset.decorator.options.class = "zend_form"
decorators.form.decorator = "Form"

The above could easily be abstracted to an XML or PHP array-based configuration file.

An alternative to using configuration-based forms is to subclass Zend_Form. This has several benefits:

The most typical use case would be to use the init() method to setup specific form elements and configuration:

class My_Form_Login extends Zend_Form
{
    public function init()
    {
        $username = new Zend_Form_Element_Text('username');
        $username->class = 'formtext';
        $username->setLabel('Username:')
                 ->setDecorators(array(
                     array('ViewHelper',
                           array('helper' => 'formText')),
                     array('Label',
                           array('class' => 'label'))
                 ));

        $password = new Zend_Form_Element_Password('password');
        $password->class = 'formtext';
        $password->setLabel('Password:')
                 ->setDecorators(array(
                     array('ViewHelper',
                           array('helper' => 'formPassword')),
                     array('Label',
                           array('class' => 'label'))
                 ));

        $submit = new Zend_Form_Element_Submit('login');
        $submit->class = 'formsubmit';
        $submit->setValue('Login')
               ->setDecorators(array(
                   array('ViewHelper',
                   array('helper' => 'formSubmit'))
               ));

        $this->addElements(array(
            $username,
            $password,
            $submit
        ));

        $this->setDecorators(array(
            'FormElements',
            'Fieldset',
            'Form'
        ));
    }
}

This form can then be instantiated with simply:

$form = new My_Form_Login();

and all functionality is already setup and ready; no config files needed. (Note that this example is greatly simplified, as it contains no validators or filters for the elements.)

Another common reason for extension is to define a set of default decorators. You can do this by overriding the loadDefaultDecorators() method:

class My_Form_Login extends Zend_Form
{
    public function loadDefaultDecorators()
    {
        $this->setDecorators(array(
            'FormElements',
            'Fieldset',
            'Form'
        ));
    }
}