repo_zf1/documentation/manual/en/module_specs/Zend_Form-Elements.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.form.elements">
    <title>Creating Form Elements Using Zend_Form_Element</title>

    <para>
        A form is made of elements that typically correspond to <acronym>HTML</acronym> form
        input. <classname>Zend_Form_Element</classname> encapsulates single form elements, with the
        following areas of responsibility:
    </para>

    <itemizedlist>
        <listitem>
            <para>
                validation (is submitted data valid?)
            </para>

            <itemizedlist>
                <listitem><para>capturing of validation error codes and messages</para></listitem>
            </itemizedlist>
        </listitem>

        <listitem>
            <para>
                filtering (how is the element escaped or normalized prior to
                validation and/or for output?)
            </para>
        </listitem>

        <listitem>
            <para>rendering (how is the element displayed?)</para>
        </listitem>

        <listitem>
            <para>metadata and attributes (what information further qualifies the element?)</para>
        </listitem>
    </itemizedlist>

    <para>
        The base class, <classname>Zend_Form_Element</classname>, has reasonable defaults
        for many cases, but it is best to extend the class for commonly used
        special purpose elements. Additionally, Zend Framework ships with a
        number of standard <acronym>XHTML</acronym> elements; you can read about them <link
            linkend="zend.form.standardElements">in the Standard Elements
            chapter</link>.
    </para>

    <sect2 id="zend.form.elements.loaders">
        <title>Plugin Loaders</title>

        <para>
            <classname>Zend_Form_Element</classname> makes use of <link
                linkend="zend.loader.pluginloader">Zend_Loader_PluginLoader</link>
            to allow developers to specify locations of alternate validators,
            filters, and decorators. Each has its own plugin loader associated
            with it, and general accessors are used to retrieve and modify
            each.
        </para>

        <para>
            The following loader types are used with the various plugin loader
            methods: 'validate', 'filter', and 'decorator'. The type names are
            case insensitive.
        </para>

        <para>
            The methods used to interact with plugin loaders are as follows:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <methodname>setPluginLoader($loader, $type)</methodname>:
                    <varname>$loader</varname> is the plugin loader object itself, while
                    <varname>$type</varname> is one of the types specified above. This
                    sets the plugin loader for the given type to the newly
                    specified loader object.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getPluginLoader($type)</methodname>: retrieves the plugin
                    loader associated with <varname>$type</varname>.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addPrefixPath($prefix, $path, $type = null)</methodname>: adds
                    a prefix/path association to the loader specified by
                    <varname>$type</varname>. If <varname>$type</varname> is
                    <constant>NULL</constant>, it will attempt to add the path to all loaders, by
                    appending the prefix with each of "_Validate", "_Filter", and "_Decorator"; and
                    appending the path with "Validate/", "Filter/", and
                    "Decorator/". If you have all your extra form element classes
                    under a common hierarchy, this is a convenience method for
                    setting the base prefix for them.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addPrefixPaths(array $spec)</methodname>: allows you to add
                    many paths at once to one or more plugin loaders. It expects
                    each array item to be an array with the keys 'path', 'prefix',
                    and 'type'.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Custom validators, filters, and decorators are an easy way to share
            functionality between forms and to encapsulate custom functionality.
        </para>

        <example id="zend.form.elements.loaders.customLabel">
            <title>Custom Label</title>

            <para>
                One common use case for plugins is to provide replacements for
                standard classes. For instance, if you want to provide a
                different implementation of the 'Label' decorator -- for
                instance, to always append a colon -- you could create your own
                'Label' decorator with your own class prefix, and then add it to
                your prefix path.
            </para>

            <para>
                Let's start with a custom Label decorator. We'll give it the
                class prefix "My_Decorator", and the class itself will be in the
                file "My/Decorator/Label.php".
            </para>

            <programlisting language="php"><![CDATA[
class My_Decorator_Label extends Zend_Form_Decorator_Abstract
{
    protected $_placement = 'PREPEND';

    public function render($content)
    {
        if (null === ($element = $this->getElement())) {
            return $content;
        }
        if (!method_exists($element, 'getLabel')) {
            return $content;
        }

        $label = $element->getLabel() . ':';

        if (null === ($view = $element->getView())) {
            return $this->renderLabel($content, $label);
        }

        $label = $view->formLabel($element->getName(), $label);

        return $this->renderLabel($content, $label);
    }

    public function renderLabel($content, $label)
    {
        $placement = $this->getPlacement();
        $separator = $this->getSeparator();

        switch ($placement) {
            case 'APPEND':
                return $content . $separator . $label;
            case 'PREPEND':
            default:
                return $label . $separator . $content;
        }
    }
}
]]></programlisting>

            <para>
                Now we can tell the element to use this plugin path when looking
                for decorators:
            </para>

            <programlisting language="php"><![CDATA[
$element->addPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');
]]></programlisting>

            <para>
                Alternately, we can do that at the form level to ensure all
                decorators use this path:
            </para>

            <programlisting language="php"><![CDATA[
$form->addElementPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');
]]></programlisting>

            <para>
                After it added as in the example above, the 'My/Decorator/' path will be searched
                first to see if the decorator exists there when you add a decorator. As a result,
                'My_Decorator_Label' will now be used when the 'Label' decorator is requested.
            </para>
        </example>
    </sect2>

    <sect2 id="zend.form.elements.filters">
        <title>Filters</title>

        <para>
            It's often useful and/or necessary to perform some normalization on
            input prior to validation. For example, you may want to strip out
            all <acronym>HTML</acronym>, but run your validations on what remains to ensure the
            submission is valid. Or you may want to trim empty space surrounding input so that a
            StringLength validator will use the correct length of the input without counting leading
            or trailing whitespace characters. These operations may be performed using
            <classname>Zend_Filter</classname>. <classname>Zend_Form_Element</classname> has support
            for filter chains, allowing you to specify multiple, sequential filters. Filtering
            happens both during validation and when you retrieve the element value via
            <methodname>getValue()</methodname>:
        </para>

        <programlisting language="php"><![CDATA[
$filtered = $element->getValue();
]]></programlisting>

        <para>
            Filters may be added to the chain in two ways:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    passing in a concrete filter instance
                </para>
            </listitem>

            <listitem>
                <para>
                    providing a short filter name
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Let's see some examples:
        </para>

        <programlisting language="php"><![CDATA[
// Concrete filter instance:
$element->addFilter(new Zend_Filter_Alnum());

// Short filter name:
$element->addFilter('Alnum');
$element->addFilter('alnum');
]]></programlisting>

        <para>
            Short names are typically the filter name minus the prefix. In the
            default case, this will mean minus the 'Zend_Filter_' prefix.
            The first letter can be upper-cased or lower-cased.
        </para>

        <note>
            <title>Using Custom Filter Classes</title>

            <para>
                If you have your own set of filter classes, you can tell
                <classname>Zend_Form_Element</classname> about these using
                <methodname>addPrefixPath()</methodname>. For instance, if you have
                filters under the 'My_Filter' prefix, you can tell
                <classname>Zend_Form_Element</classname> about this as follows:
            </para>

            <programlisting language="php"><![CDATA[
$element->addPrefixPath('My_Filter', 'My/Filter/', 'filter');
]]></programlisting>

            <para>
                (Recall that the third argument indicates which plugin loader
                on which to perform the action.)
            </para>
        </note>

        <para>
            If at any time you need the unfiltered value, use the
            <methodname>getUnfilteredValue()</methodname> method:
        </para>

        <programlisting language="php"><![CDATA[
$unfiltered = $element->getUnfilteredValue();
]]></programlisting>

        <para>
            For more information on filters, see the <link
                linkend="zend.filter.introduction">Zend_Filter
                documentation</link>.
        </para>

        <para>
            Methods associated with filters include:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <methodname>addFilter($nameOfFilter, array $options = null)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addFilters(array $filters)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setFilters(array $filters)</methodname> (overwrites all filters)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getFilter($name)</methodname> (retrieve a filter object by name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getFilters()</methodname> (retrieve all filters)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>removeFilter($name)</methodname> (remove filter by name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>clearFilters()</methodname> (remove all filters)
                </para>
            </listitem>
        </itemizedlist>
    </sect2>

    <sect2 id="zend.form.elements.validators">
        <title>Validators</title>

        <para>
            If you subscribe to the security mantra of "filter input, escape
            output," you'll should use validator to filter input submitted with your form.
            In <classname>Zend_Form</classname>, each element includes its own validator
            chain, consisting of <classname>Zend_Validate_*</classname> validators.
        </para>

        <para>
            Validators may be added to the chain in two ways:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    passing in a concrete validator instance
                </para>
            </listitem>

            <listitem>
                <para>
                    providing a short validator name
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Let's see some examples:
        </para>

        <programlisting language="php"><![CDATA[
// Concrete validator instance:
$element->addValidator(new Zend_Validate_Alnum());

// Short validator name:
$element->addValidator('Alnum');
$element->addValidator('alnum');
]]></programlisting>

        <para>
            Short names are typically the validator name minus the prefix. In
            the default case, this will mean minus the 'Zend_Validate_' prefix.
            As is the case with filters, the first letter can be upper-cased or lower-cased.
        </para>

        <note>
            <title>Using Custom Validator Classes</title>

            <para>
                If you have your own set of validator classes, you can tell
                <classname>Zend_Form_Element</classname> about these using
                <methodname>addPrefixPath()</methodname>. For instance, if you have
                validators under the 'My_Validator' prefix, you can tell
                <classname>Zend_Form_Element</classname> about this as follows:
            </para>

            <programlisting language="php"><![CDATA[
$element->addPrefixPath('My_Validator', 'My/Validator/', 'validate');
]]></programlisting>

            <para>
                (Recall that the third argument indicates which plugin loader
                on which to perform the action.)
            </para>
        </note>

        <para>
            If failing a particular validation should prevent later validators
            from firing, pass boolean <constant>TRUE</constant> as the second parameter:
        </para>

        <programlisting language="php"><![CDATA[
$element->addValidator('alnum', true);
]]></programlisting>

        <para>
            If you are using a string name to add a validator, and the
            validator class accepts arguments to the constructor, you may pass
            these to the third parameter of <methodname>addValidator()</methodname> as an
            array:
        </para>

        <programlisting language="php"><![CDATA[
$element->addValidator('StringLength', false, array(6, 20));
]]></programlisting>

        <para>
            Arguments passed in this way should be in the order in which they
            are defined in the constructor. The above example will instantiate
            the <classname>Zend_Validate_StringLenth</classname> class with its
            <varname>$min</varname> and <varname>$max</varname> parameters:
        </para>

        <programlisting language="php"><![CDATA[
$validator = new Zend_Validate_StringLength(6, 20);
]]></programlisting>

        <note>
            <title>Providing Custom Validator Error Messages</title>

            <para>
                Some developers may wish to provide custom error messages for a
                validator. The <varname>$options</varname> argument of the
                <methodname>Zend_Form_Element::addValidator()</methodname> method allows you to do
                so by providing the key 'messages' and mapping it to an array of key/value pairs
                for setting the message templates. You will need to know the
                error codes of the various validation error types for the
                particular validator.
            </para>

            <para>
                A better option is to use a <classname>Zend_Translate_Adapter</classname>
                with your form. Error codes are automatically passed to the
                adapter by the default Errors decorator; you can then specify
                your own error message strings by setting up translations for
                the various error codes of your validators.
            </para>
        </note>

        <para>
            You can also set many validators at once, using
            <methodname>addValidators()</methodname>. The basic usage is to pass an array
            of arrays, with each array containing 1 to 3 values, matching the
            constructor of <methodname>addValidator()</methodname>:
        </para>

        <programlisting language="php"><![CDATA[
$element->addValidators(array(
    array('NotEmpty', true),
    array('alnum'),
    array('stringLength', false, array(6, 20)),
));
]]></programlisting>

        <para>
            If you want to be more verbose or explicit, you can use the array
            keys 'validator', 'breakChainOnFailure', and 'options':
        </para>

        <programlisting language="php"><![CDATA[
$element->addValidators(array(
    array(
        'validator'           => 'NotEmpty',
        'breakChainOnFailure' => true),
    array('validator' => 'alnum'),
    array(
        'validator' => 'stringLength',
        'options'   => array(6, 20)),
));
]]></programlisting>

        <para>
            This usage is good for illustrating how you could then configure
            validators in a config file:
        </para>

        <programlisting language="ini"><![CDATA[
element.validators.notempty.validator = "NotEmpty"
element.validators.notempty.breakChainOnFailure = true
element.validators.alnum.validator = "Alnum"
element.validators.strlen.validator = "StringLength"
element.validators.strlen.options.min = 6
element.validators.strlen.options.max = 20
]]></programlisting>

        <para>
            Notice that every item has a key, whether or not it needs one; this
            is a limitation of using configuration files -- but it also helps
            make explicit what the arguments are for. Just remember that any
            validator options must be specified in order.
        </para>

        <para>
            To validate an element, pass the value to
            <methodname>isValid()</methodname>:
        </para>

        <programlisting language="php"><![CDATA[
if ($element->isValid($value)) {
    // valid
} else {
    // invalid
}
]]></programlisting>

        <note>
            <title>Validation Operates On Filtered Values</title>

            <para>
                <methodname>Zend_Form_Element::isValid()</methodname> filters values through
                the provided filter chain prior to validation. See <link
                    linkend="zend.form.elements.filters">the Filters
                    section</link> for more information.
            </para>
        </note>

        <note>
            <title>Validation Context</title>

            <para>
                <methodname>Zend_Form_Element::isValid()</methodname> supports an
                additional argument, <varname>$context</varname>.
                <methodname>Zend_Form::isValid()</methodname> passes the entire array of
                data being processed to <varname>$context</varname> when validating a
                form, and <methodname>Zend_Form_Element::isValid()</methodname>, in turn,
                passes it to each validator. This means you can write
                validators that are aware of data passed to other form
                elements. As an example, consider a standard registration form
                that has fields for both password and a password confirmation;
                one validation would be that the two fields match. Such a
                validator might look like the following:
            </para>

            <programlisting language="php"><![CDATA[
class My_Validate_PasswordConfirmation extends Zend_Validate_Abstract
{
    const NOT_MATCH = 'notMatch';

    protected $_messageTemplates = array(
        self::NOT_MATCH => 'Password confirmation does not match'
    );

    public function isValid($value, $context = null)
    {
        $value = (string) $value;
        $this->_setValue($value);

        if (is_array($context)) {
            if (isset($context['password_confirm'])
                && ($value == $context['password_confirm']))
            {
                return true;
            }
        } elseif (is_string($context) && ($value == $context)) {
            return true;
        }

        $this->_error(self::NOT_MATCH);
        return false;
    }
}
]]></programlisting>
        </note>

        <para>
            Validators are processed in order. Each validator is processed,
            unless a validator created with a <constant>TRUE</constant>
            <varname>$breakChainOnFailure</varname> value fails its validation. Be
            sure to specify your validators in a reasonable order.
        </para>

        <para>
            After a failed validation, you can retrieve the error codes and
            messages from the validator chain:
        </para>

        <programlisting language="php"><![CDATA[
$errors   = $element->getErrors();
$messages = $element->getMessages();
]]></programlisting>

        <para>
            (Note: error messages returned are an associative array of error
            code / error message pairs.)
        </para>

        <para>
            In addition to validators, you can specify that an element is
            required, using <methodname>setRequired($flag)</methodname>. By default, this
            flag is <constant>FALSE</constant>. In combination with
            <methodname>setAllowEmpty($flag)</methodname> (<constant>TRUE</constant>
            by default) and <methodname>setAutoInsertNotEmptyValidator($flag)</methodname>
            (<constant>TRUE</constant> by default), the behavior of your validator chain
            can be modified in a number of ways:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    Using the defaults, validating an Element without passing a value, or
                    passing an empty string for it, skips all validators and validates to
                    <constant>TRUE</constant>.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setAllowEmpty(false)</methodname> leaving the two other
                    mentioned flags untouched, will validate against the validator chain
                    you defined for this Element, regardless of the value passed
                    to <methodname>isValid()</methodname>.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setRequired(true)</methodname> leaving the two other
                    mentioned flags untouched, will add a 'NotEmpty' validator
                    on top of the validator chain (if none was already set)), with the
                    <varname>$breakChainOnFailure</varname> flag set. This behavior lends
                    required flag semantic meaning: if no value is passed,
                    we immediately invalidate the submission and notify the
                    user, and prevent other validators from running on what we
                    already know is invalid data.
                </para>

                <para>
                    If you do not want this behavior, you can turn it off by
                    passing a <constant>FALSE</constant> value to
                    <methodname>setAutoInsertNotEmptyValidator($flag)</methodname>; this
                    will prevent <methodname>isValid()</methodname> from placing the
                    'NotEmpty' validator in the validator chain.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            For more information on validators, see the <link
                linkend="zend.validate.introduction">Zend_Validate
                documentation</link>.
        </para>

        <note>
            <title>Using Zend_Form_Elements as general-purpose validators</title>

            <para>
                <classname>Zend_Form_Element</classname> implements
                <classname>Zend_Validate_Interface</classname>, meaning an element may
                also be used as a validator in other, non-form related
                validation chains.
            </para>
        </note>

        <note>
            <title>When is an element detected as empty?</title>

            <para>
                As mentioned the 'NotEmpty' validator is used to detect if an element is empty
                or not. But <classname>Zend_Validate_NotEmpty</classname> does, per default, not
                work like <acronym>PHP</acronym>'s method <methodname>empty()</methodname>.
            </para>

            <para>
                This means when an element contains an integer <emphasis>0</emphasis> or an string
                <emphasis>'0'</emphasis> then the element will be seen as not empty. If you want to
                have a different behaviour you must create your own instance of
                <classname>Zend_Validate_NotEmpty</classname>. There you can define the behaviour of
                this validator. See <ulink
                    url="zend.validate.set.notempty">Zend_Validate_NotEmpty</ulink> for details.
            </para>
        </note>

        <para>
            Methods associated with validation include:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <methodname>setRequired($flag)</methodname> and
                    <methodname>isRequired()</methodname> allow you to set and retrieve the
                    status of the 'required' flag. When set to boolean <constant>TRUE</constant>,
                    this flag requires that the element be in the data processed by
                    <classname>Zend_Form</classname>.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setAllowEmpty($flag)</methodname> and
                    <methodname>getAllowEmpty()</methodname> allow you to modify the
                    behaviour of optional elements (i.e., elements where the
                    required flag is <constant>FALSE</constant>). When the 'allow empty' flag is
                    <constant>TRUE</constant>, empty values will not be passed to the validator
                    chain.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setAutoInsertNotEmptyValidator($flag)</methodname> allows
                    you to specify whether or not a 'NotEmpty' validator will be
                    prepended to the validator chain when the element is
                    required. By default, this flag is <constant>TRUE</constant>.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addValidator($nameOrValidator, $breakChainOnFailure = false, array
                        $options = null)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addValidators(array $validators)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setValidators(array $validators)</methodname> (overwrites all
                    validators)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getValidator($name)</methodname> (retrieve a validator object by
                    name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getValidators()</methodname> (retrieve all validators)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>removeValidator($name)</methodname> (remove validator by name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>clearValidators()</methodname> (remove all validators)
                </para>
            </listitem>
        </itemizedlist>

        <sect3 id="zend.form.elements.validators.errors">
            <title>Custom Error Messages</title>

            <para>
                At times, you may want to specify one or more specific error
                messages to use instead of the error messages generated by the
                validators attached to your element. Additionally, at times you
                may want to mark the element invalid yourself. As of 1.6.0, this
                functionality is possible via the following methods.
            </para>

            <itemizedlist>
                <listitem>
                    <para>
                        <methodname>addErrorMessage($message)</methodname>: add an error message
                        to display on form validation errors. You may call this more
                        than once, and new messages are appended to the stack.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>addErrorMessages(array $messages)</methodname>: add multiple
                        error messages to display on form validation errors.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>setErrorMessages(array $messages)</methodname>: add multiple
                        error messages to display on form validation errors,
                        overwriting all previously set error messages.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>getErrorMessages()</methodname>: retrieve the list of
                        custom error messages that have been defined.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>clearErrorMessages()</methodname>: remove all custom error
                        messages that have been defined.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>markAsError()</methodname>: mark the element as having
                        failed validation.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>hasErrors()</methodname>: determine whether the element has
                        either failed validation or been marked as invalid.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>addError($message)</methodname>: add a message to the custom
                        error messages stack and flag the element as invalid.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>addErrors(array $messages)</methodname>: add several
                        messages to the custom error messages stack and flag the
                        element as invalid.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        <methodname>setErrors(array $messages)</methodname>: overwrite the
                        custom error messages stack with the provided messages and
                        flag the element as invalid.
                    </para>
                </listitem>
            </itemizedlist>

            <para>
                All errors set in this fashion may be translated. Additionally,
                you may insert the placeholder "%value%" to represent the
                element value; this current element value will be substituted
                when the error messages are retrieved.
            </para>
        </sect3>
    </sect2>

    <sect2 id="zend.form.elements.decorators">
        <title>Decorators</title>

        <para>
            One particular pain point for many web developers is the creation
            of the <acronym>XHTML</acronym> forms themselves. For each element, the developer
            needs to create markup for the element itself (typically a label)
            and special markup for displaying
            validation error messages. The more elements on the page, the less
            trivial this task becomes.
        </para>

        <para>
            <classname>Zend_Form_Element</classname> tries to solve this issue through
            the use of "decorators". Decorators are simply classes that have
            access to the element and a method for rendering content. For more
            information on how decorators work, please see the section on <link
                linkend="zend.form.decorators">Zend_Form_Decorator</link>.
        </para>

        <para>
            The default decorators used by <classname>Zend_Form_Element</classname> are:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <emphasis>ViewHelper</emphasis>: specifies a view helper to use
                    to render the element. The 'helper' element attribute can be
                    used to specify which view helper to use. By default,
                    <classname>Zend_Form_Element</classname> specifies the 'formText' view
                    helper, but individual subclasses specify different helpers.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>Errors</emphasis>: appends error messages to the
                    element using <classname>Zend_View_Helper_FormErrors</classname>. If none are
                    present, nothing is appended.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>Description</emphasis>: appends the element
                    description. If none is present, nothing is appended. By
                    default, the description is rendered in a &lt;p&gt; tag with a
                    class of 'description'.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>HtmlTag</emphasis>: wraps the element and errors in
                    an <acronym>HTML</acronym> &lt;dd&gt; tag.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>Label</emphasis>: prepends a label to the element
                    using <classname>Zend_View_Helper_FormLabel</classname>, and wraps it in a
                    &lt;dt&gt; tag. If no label is provided, just the definition term tag is
                    rendered.
                </para>
            </listitem>
        </itemizedlist>

        <note>
            <title>Default Decorators Do Not Need to Be Loaded</title>

            <para>
                By default, the default decorators are loaded during object
                initialization. You can disable this by passing the
                'disableLoadDefaultDecorators' option to the constructor:
            </para>

            <programlisting language="php"><![CDATA[
$element = new Zend_Form_Element('foo',
                                 array('disableLoadDefaultDecorators' =>
                                      true)
                                );
]]></programlisting>

            <para>
                This option may be mixed with any other options you pass,
                both as array options or in a <classname>Zend_Config</classname> object.
            </para>
        </note>

        <para>
            Since the order in which decorators are registered matters- the first
            decorator registered is executed first- you will need to make
            sure you register your decorators in an appropriate order, or
            ensure that you set the placement options in a sane fashion. To
            give an example, here is the code that registers the default
            decorators:
        </para>

        <programlisting language="php"><![CDATA[
$this->addDecorators(array(
    array('ViewHelper'),
    array('Errors'),
    array('Description', array('tag' => 'p', 'class' => 'description')),
    array('HtmlTag', array('tag' => 'dd')),
    array('Label', array('tag' => 'dt')),
));
]]></programlisting>

        <para>
            The initial content is created by the 'ViewHelper' decorator, which
            creates the form element itself. Next, the 'Errors' decorator
            fetches error messages from the element, and, if any are present,
            passes them to the 'FormErrors' view helper to render. If a
            description is present, the 'Description' decorator will append a
            paragraph of class 'description' containing the descriptive text to
            the aggregated content. The next decorator, 'HtmlTag', wraps the
            element, errors, and description in an <acronym>HTML</acronym> &lt;dd&gt; tag.
            Finally, the last decorator, 'label', retrieves the element's label
            and passes it to the 'FormLabel' view helper, wrapping it in an <acronym>HTML</acronym>
            &lt;dt&gt; tag; the value is prepended to the content by default.
            The resulting output looks basically like this:
        </para>

        <programlisting language="html"><![CDATA[
<dt><label for="foo" class="optional">Foo</label></dt>
<dd>
    <input type="text" name="foo" id="foo" value="123" />
    <ul class="errors">
        <li>"123" is not an alphanumeric value</li>
    </ul>
    <p class="description">
        This is some descriptive text regarding the element.
    </p>
</dd>
]]></programlisting>

        <para>
            For more information on decorators, read the <link
                linkend="zend.form.decorators">Zend_Form_Decorator section</link>.
        </para>

        <note>
            <title>Using Multiple Decorators of the Same Type</title>

            <para>
                Internally, <classname>Zend_Form_Element</classname> uses a decorator's
                class as the lookup mechanism when retrieving decorators. As a
                result, you cannot register multiple decorators of the same
                type; subsequent decorators will simply overwrite those that
                existed before.
            </para>

            <para>
                To get around this, you can use <emphasis>aliases</emphasis>.
                Instead of passing a decorator or decorator name as the first
                argument to <methodname>addDecorator()</methodname>, pass an array with a
                single element, with the alias pointing to the decorator object
                or name:
            </para>

            <programlisting language="php"><![CDATA[
// Alias to 'FooBar':
$element->addDecorator(array('FooBar' => 'HtmlTag'),
                       array('tag' => 'div'));

// And retrieve later:
$decorator = $element->getDecorator('FooBar');
]]></programlisting>

            <para>
                In the <methodname>addDecorators()</methodname> and
                <methodname>setDecorators()</methodname> methods, you will need to pass
                the 'decorator' option in the array representing the decorator:
            </para>

            <programlisting language="php"><![CDATA[
// Add two 'HtmlTag' decorators, aliasing one to 'FooBar':
$element->addDecorators(
    array('HtmlTag', array('tag' => 'div')),
    array(
        'decorator' => array('FooBar' => 'HtmlTag'),
        'options' => array('tag' => 'dd')
    ),
);

// And retrieve later:
$htmlTag = $element->getDecorator('HtmlTag');
$fooBar  = $element->getDecorator('FooBar');
]]></programlisting>
        </note>

        <para>
            Methods associated with decorators include:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <methodname>addDecorator($nameOrDecorator, array $options = null)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>addDecorators(array $decorators)</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>setDecorators(array $decorators)</methodname> (overwrites all
                    decorators)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getDecorator($name)</methodname> (retrieve a decorator object by
                    name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getDecorators()</methodname> (retrieve all decorators)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>removeDecorator($name)</methodname> (remove decorator by name)
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>clearDecorators()</methodname> (remove all decorators)
                </para>
            </listitem>
        </itemizedlist>

        <para>
            <classname>Zend_Form_Element</classname> also uses overloading to allow rendering
            specific decorators. <methodname>__call()</methodname> 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
            <emphasis>single</emphasis> decorator. Any arguments passed to the
            method call will be used as content to pass to the decorator's
            <methodname>render()</methodname> method. As an example:
        </para>

        <programlisting language="php"><![CDATA[
// Render only the ViewHelper decorator:
echo $element->renderViewHelper();

// Render only the HtmlTag decorator, passing in content:
echo $element->renderHtmlTag("This is the html tag content");
]]></programlisting>

        <para>
            If the decorator does not exist, an exception is raised.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.metadata">
        <title>Metadata and Attributes</title>

        <para>
            <classname>Zend_Form_Element</classname> handles a variety of attributes and
            element metadata. Basic attributes include:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <emphasis>name</emphasis>: the element name. Uses the
                    <methodname>setName()</methodname> and <methodname>getName()</methodname>
                    accessors.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>label</emphasis>: the element label. Uses the
                    <methodname>setLabel()</methodname> and <methodname>getLabel()</methodname>
                    accessors.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>order</emphasis>: the index at which an element
                    should appear in the form. Uses the <methodname>setOrder()</methodname> and
                    <methodname>getOrder()</methodname> accessors.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>value</emphasis>: the current element value. Uses the
                    <methodname>setValue()</methodname> and <methodname>getValue()</methodname>
                    accessors.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>description</emphasis>: a description of the element;
                    often used to provide tooltip or javascript contextual hinting
                    describing the purpose of the element. Uses the
                    <methodname>setDescription()</methodname> and
                    <methodname>getDescription()</methodname> accessors.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>required</emphasis>: flag indicating whether or not
                    the element is required when performing form validation. Uses
                    the <methodname>setRequired()</methodname> and
                    <methodname>isRequired()</methodname> accessors. This flag is
                    <constant>FALSE</constant> by default.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>allowEmpty</emphasis>: flag indicating whether or not
                    a non-required (optional) element should attempt to validate
                    empty values. If it is set to <constant>TRUE</constant> and the required flag is
                    <constant>FALSE</constant>, empty values are not passed to the validator chain
                    and are presumed <constant>TRUE</constant>. Uses the
                    <methodname>setAllowEmpty()</methodname> and
                    <methodname>getAllowEmpty()</methodname> accessors. This flag is
                    <constant>TRUE</constant> by default.
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>autoInsertNotEmptyValidator</emphasis>: flag
                    indicating whether or not to insert a 'NotEmpty' validator when
                    the element is required. By default, this flag is <constant>TRUE</constant>. Set
                    the flag with <methodname>setAutoInsertNotEmptyValidator($flag)</methodname> and
                    determine the value with
                    <methodname>autoInsertNotEmptyValidator()</methodname>.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Form elements may require additional metadata. For <acronym>XHTML</acronym> form
            elements, for instance, you may want to specify attributes such as
            the class or id. To facilitate this are a set of accessors:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <emphasis>setAttrib($name, $value)</emphasis>: add an attribute
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>setAttribs(array $attribs)</emphasis>: like
                    addAttribs(), but overwrites
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>getAttrib($name)</emphasis>: retrieve a single
                    attribute value
                </para>
            </listitem>

            <listitem>
                <para>
                    <emphasis>getAttribs()</emphasis>: retrieve all attributes as
                    key/value pairs
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Most of the time, however, you can simply access them as object
            properties, as <classname>Zend_Form_Element</classname> utilizes overloading
            to facilitate access to them:
        </para>

        <programlisting language="php"><![CDATA[
// Equivalent to $element->setAttrib('class', 'text'):
$element->class = 'text;
]]></programlisting>

        <para>
            By default, all attributes are passed to the view helper used by
            the element during rendering, and rendered as <acronym>HTML</acronym> attributes of
            the element tag.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.standard">
        <title>Standard Elements</title>

        <para>
            <classname>Zend_Form</classname> ships with a number of standard elements; please read
            the <link linkend="zend.form.standardElements">Standard Elements</link>
            chapter for full details.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.methods">
        <title>Zend_Form_Element Methods</title>

        <para>
            <classname>Zend_Form_Element</classname> has many, many methods. What follows
            is a quick summary of their signatures, grouped by type:
        </para>

        <itemizedlist>
            <listitem>
                <para>Configuration:</para>

                <itemizedlist>
                    <listitem>
                        <para><methodname>setOptions(array $options)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>setConfig(Zend_Config $config)</methodname></para>
                    </listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>I18n:</para>

                <itemizedlist>
                    <listitem>
                        <para>
                            <methodname>setTranslator(Zend_Translate_Adapter $translator
                                = null)</methodname>
                        </para>
                    </listitem>

                    <listitem><para><methodname>getTranslator()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>setDisableTranslator($flag)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>translatorIsDisabled()</methodname></para>
                    </listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>Properties:</para>

                <itemizedlist>
                    <listitem><para><methodname>setName($name)</methodname></para></listitem>
                    <listitem><para><methodname>getName()</methodname></para></listitem>
                    <listitem><para><methodname>setValue($value)</methodname></para></listitem>
                    <listitem><para><methodname>getValue()</methodname></para></listitem>
                    <listitem><para><methodname>getUnfilteredValue()</methodname></para></listitem>
                    <listitem><para><methodname>setLabel($label)</methodname></para></listitem>
                    <listitem><para><methodname>getLabel()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>setDescription($description)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getDescription()</methodname></para></listitem>
                    <listitem><para><methodname>setOrder($order)</methodname></para></listitem>
                    <listitem><para><methodname>getOrder()</methodname></para></listitem>
                    <listitem><para><methodname>setRequired($flag)</methodname></para></listitem>
                    <listitem><para><methodname>isRequired()</methodname></para></listitem>
                    <listitem><para><methodname>setAllowEmpty($flag)</methodname></para></listitem>
                    <listitem><para><methodname>getAllowEmpty()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>setAutoInsertNotEmptyValidator($flag)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>autoInsertNotEmptyValidator()</methodname></para>
                    </listitem>

                    <listitem><para><methodname>setIgnore($flag)</methodname></para></listitem>
                    <listitem><para><methodname>getIgnore()</methodname></para></listitem>
                    <listitem><para><methodname>getType()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>setAttrib($name, $value)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>setAttribs(array $attribs)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getAttrib($name)</methodname></para></listitem>
                    <listitem><para><methodname>getAttribs()</methodname></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>Plugin loaders and paths:</para>

                <itemizedlist>
                    <listitem>
                        <para>
                            <methodname>setPluginLoader(Zend_Loader_PluginLoader_Interface $loader,
                                $type)</methodname>
                        </para>
                    </listitem>

                    <listitem>
                        <para><methodname>getPluginLoader($type)</methodname></para>
                    </listitem>

                    <listitem>
                        <para>
                            <methodname>addPrefixPath($prefix, $path, $type = null)</methodname>
                        </para>
                    </listitem>

                    <listitem>
                        <para><methodname>addPrefixPaths(array $spec)</methodname></para>
                    </listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>Validation:</para>

                <itemizedlist>
                    <listitem>
                        <para>
                            <methodname>addValidator($validator, $breakChainOnFailure = false,
                                $options = array())</methodname>
                        </para>
                    </listitem>

                    <listitem>
                        <para><methodname>addValidators(array $validators)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>setValidators(array $validators)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getValidator($name)</methodname></para></listitem>
                    <listitem><para><methodname>getValidators()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>removeValidator($name)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>clearValidators()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>isValid($value, $context = null)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getErrors()</methodname></para></listitem>
                    <listitem><para><methodname>getMessages()</methodname></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>Filters:</para>

                <itemizedlist>
                    <listitem>
                        <para><methodname>addFilter($filter, $options = array())</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>addFilters(array $filters)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>setFilters(array $filters)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getFilter($name)</methodname></para></listitem>
                    <listitem><para><methodname>getFilters()</methodname></para></listitem>
                    <listitem><para><methodname>removeFilter($name)</methodname></para></listitem>
                    <listitem><para><methodname>clearFilters()</methodname></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem>
                <para>Rendering:</para>

                <itemizedlist>
                    <listitem>
                        <para>
                            <methodname>setView(Zend_View_Interface $view = null)</methodname>
                        </para>
                    </listitem>

                    <listitem><para><methodname>getView()</methodname></para></listitem>

                    <listitem>
                        <para>
                            <methodname>addDecorator($decorator, $options = null)</methodname>
                        </para>
                    </listitem>

                    <listitem>
                        <para><methodname>addDecorators(array $decorators)</methodname></para>
                    </listitem>

                    <listitem>
                        <para><methodname>setDecorators(array $decorators)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>getDecorator($name)</methodname></para></listitem>
                    <listitem><para><methodname>getDecorators()</methodname></para></listitem>

                    <listitem>
                        <para><methodname>removeDecorator($name)</methodname></para>
                    </listitem>

                    <listitem><para><methodname>clearDecorators()</methodname></para></listitem>

                    <listitem>
                        <para>
                            <methodname>render(Zend_View_Interface $view = null)</methodname>
                        </para>
                    </listitem>
                </itemizedlist>
            </listitem>
        </itemizedlist>
    </sect2>

    <sect2 id="zend.form.elements.config">
        <title>Configuration</title>

        <para>
            <classname>Zend_Form_Element</classname>'s constructor accepts either an
            array of options or a <classname>Zend_Config</classname> object containing
            options, and it can also be configured using either
            <methodname>setOptions()</methodname> or <methodname>setConfig()</methodname>. Generally
            speaking, keys are named as follows:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    If 'set' + key refers to a <classname>Zend_Form_Element</classname>
                    method, then the value provided will be passed to that method.
                </para>
            </listitem>

            <listitem>
                <para>
                    Otherwise, the value will be used to set an attribute.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Exceptions to the rule include the following:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <property>prefixPath</property> will be passed to
                    <methodname>addPrefixPaths()</methodname>
                </para>
            </listitem>

            <listitem>
                <para>
                    The following setters cannot be set in this way:
                </para>

                <itemizedlist>
                    <listitem>
                        <para>
                            <property>setAttrib</property> (though
                            <property>setAttribs</property> <emphasis>will</emphasis> work)
                        </para>
                    </listitem>

                    <listitem><para><property>setConfig</property></para></listitem>
                    <listitem><para><property>setOptions</property></para></listitem>
                    <listitem><para><property>setPluginLoader</property></para></listitem>
                    <listitem><para><property>setTranslator</property></para></listitem>
                    <listitem><para><property>setView</property></para></listitem>
                </itemizedlist>
            </listitem>
        </itemizedlist>

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

        <programlisting language="ini"><![CDATA[
[element]
name = "foo"
value = "foobar"
label = "Foo:"
order = 10
required = true
allowEmpty = false
autoInsertNotEmptyValidator = true
description = "Foo elements are for examples"
ignore = false
attribs.id = "foo"
attribs.class = "element"
; For radio button elements
escape = true
listsep = "<br />\n"
; sets 'onclick' attribute
onclick = "autoComplete(this, '/form/autocomplete/element')"
prefixPaths.decorator.prefix = "My_Decorator"
prefixPaths.decorator.path = "My/Decorator/"
disableTranslator = 0
validators.required.validator = "NotEmpty"
validators.required.breakChainOnFailure = true
validators.alpha.validator = "alpha"
validators.regex.validator = "regex"
validators.regex.options.pattern = "/^[A-F].*/$"
filters.ucase.filter = "StringToUpper"
decorators.element.decorator = "ViewHelper"
decorators.element.options.helper = "FormText"
decorators.label.decorator = "Label"
]]></programlisting>
    </sect2>

    <sect2 id="zend.form.elements.custom">
        <title>Custom Elements</title>

        <para>
            You can create your own custom elements by simply extending the
            <classname>Zend_Form_Element</classname> class. Common reasons to do so
            include:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    Elements that share common validators and/or filters
                </para>
            </listitem>

            <listitem>
                <para>
                    Elements that have custom decorator functionality
                </para>
            </listitem>
        </itemizedlist>

        <para>
            There are two methods typically used to extend an element:
            <methodname>init()</methodname>, which can be used to add custom initialization
            logic to your element, and <methodname>loadDefaultDecorators()</methodname>,
            which can be used to set a list of default decorators used by your
            element.
        </para>

        <para>
            As an example, let's say that all text elements in a form you are
            creating need to be filtered with <classname>StringTrim</classname>,
            validated with a common regular expression, and that you want to
            use a custom decorator you've created for displaying them,
            'My_Decorator_TextItem'. In addition, you have a number of standard
            attributes, including 'size', 'maxLength', and 'class' you wish to
            specify. You could define an element to accomplish this as follows:
        </para>

        <programlisting language="php"><![CDATA[
class My_Element_Text extends Zend_Form_Element
{
    public function init()
    {
        $this->addPrefixPath('My_Decorator', 'My/Decorator/', 'decorator')
             ->addFilters('StringTrim')
             ->addValidator('Regex', false, array('/^[a-z0-9]{6,}$/i'))
             ->addDecorator('TextItem')
             ->setAttrib('size', 30)
             ->setAttrib('maxLength', 45)
             ->setAttrib('class', 'text');
    }
}
]]></programlisting>

        <para>
            You could then inform your form object about the prefix path for
            such elements, and start creating elements:
        </para>

        <programlisting language="php"><![CDATA[
$form->addPrefixPath('My_Element', 'My/Element/', 'element')
     ->addElement('text', 'foo');
]]></programlisting>

        <para>
            The 'foo' element will now be of type <classname>My_Element_Text</classname>,
            and exhibit the behaviour you've outlined.
        </para>

        <para>
            Another method you may want to override when extending
            <classname>Zend_Form_Element</classname> is the
            <methodname>loadDefaultDecorators()</methodname> method. This method
            conditionally loads a set of default decorators for your element;
            you may wish to substitute your own decorators in your extending
            class:
        </para>

        <programlisting language="php"><![CDATA[
class My_Element_Text extends Zend_Form_Element
{
    public function loadDefaultDecorators()
    {
        $this->addDecorator('ViewHelper')
             ->addDecorator('DisplayError')
             ->addDecorator('Label')
             ->addDecorator('HtmlTag',
                            array('tag' => 'div', 'class' => 'element'));
    }
}
]]></programlisting>

        <para>
            There are many ways to customize elements. Read the <acronym>API</acronym>
            documentation of <classname>Zend_Form_Element</classname> to learn about all of the
            available methods.
        </para>
    </sect2>
</sect1>
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