Zend_Form

<?php
class Forms_LpaManageEmailForm extends Zend_Form
{
    protected $_actionUrl;
    protected $_entry_id;
    protected $_flag;


    public function __construct($actionUrl, $options=null, $entry_id, $flag)
    {
        $this->addPrefixPath('ZFBlog_Form_Decorator', 'ZFBlog/Form/Decorator/', 'decorator');

        parent::__construct($options);
        $this->setActionUrl($actionUrl);
        $this->setEntryId($entry_id);
        $this->setFlag($flag);
        $this->init();
    }

    public function setActionUrl($actionUrl) {

        $this->_actionUrl = $actionUrl;
        return $this;
    }

    public function setEntryId($entry_id){
        $this->_entry_id = $entry_id;
        return $this;
    }

    public function getEntryId(){
        return $this->_entry_id['entry_id'];
    }

    public function setFlag($flag) {
        $this->_flag = $flag;
    }

    public function getFlag() {
        return $this->_flag;
    }


    public function init()
    {

        $this->setAction($this->_actionUrl)
             ->setMethod('post')
             ->setAttribs(array('id' => 'descriptionform', 'onSubmit' => 'multipleSelectOnSubmit()'));

        $this->clearDecorators();


    ...

        $this->addElement('hidden', 'id', array(
            'validators' => array(
                'Digits'
            ),
            'required' => true,
            'value' => $this->_entry_id['entry_id'],
        ));

        ...

        $this->addElement($submit);


       ...
    }


    private function _addMultiOptionsForMultiSelect()
    {
            ...
    }

    public function render(Zend_View_Interface $view = null)
    {
        $this->_addMultiOptionsForMultiSelect();

        return parent::render($view);
    }

    public function isValid($data)
    {
        $this->_addMultiOptionsForMultiSelect();

        return parent::isValid($data);
    }

}

<?php
class Default_Form_CartReport extends Forms_LpaManageEmailForm
{
    protected $_orderId;

    public function __construct($actionUrl, $options=null, $entry_id, $flag=null, $orderId)
    {
        $this->setOrderId($orderId);
        parent::__construct($actionUrl, $options=null, $entry_id, $flag);
    }

    public function setOrderId($orderId){

        $this->_orderId = $orderId;
        return $this;
    }

    public function setValue($value)
    {
        $strippedValue = stripslashes($value);
        return parent::setValue($strippedValue);
    }

    public function init(){
        parent::init();
        $this->id->setValue('100'); // experimental method. doesn't work... debugger shows
         //["_value":protected] => string(3) "100" ,  but in HTML output it's empty

       /* $this->addElement('hidden', 'id', array(
                'validators' => array(
                        'Digits'
                ),
                'required' => true,
                'value' => '100',
        ));*/ creating the element with the same name doesn't make any sense

        Zend_Debug::dump($this->getElements());

    }

    private function _addMultiOptionsForMultiSelect()
    {
       ...

    }

    public function render(Zend_View_Interface $view = null)
    {
        $this->_addMultiOptionsForMultiSelect();

        return Zend_Form::render($view);
    }

    public function isValid($data)
    {
        $this->_addMultiOptionsForMultiSelect();

        return Zend_Form::isValid($data);
    }

}