use bcspamblock in zend form

I want to integrate the bcspamblock and zend form, so first to do:
为了能自动防止机器人攻击，打算把bcspamblock整合到zend_form中。
1 创建element_bcSpamBlock.php文件，

<?php
class element_bcSpamBlock extends Zend_Form_Element_Xhtml{
    /**
     * Default form view helper to use for rendering
     * @var string
     */
    public $helper = 'bcSpamBlock';   
}

2 创建helper文件：BcSpamBlock.php

<?php
include_once("bcspamblock.php");
class Zend_View_Helper_BcSpamBlock extends Zend_View_Helper_FormElement{

    public function bcSpamBlock($name, $value='', $attribs = null){
       
        $xhtml = bcspamblock_generate(true);
        return $xhtml;
    }
}

3 创建validator，但奇怪的是，这一步经测试，没发生实际作用，不知道是什么原因。

<?php
include_once("bcspamblock.php");
class Validator_SpamBlock extends Zend_Validate_Abstract {
    const NOT_MATCH = '机器人阻止';//'spam blocked!';

    protected $_messageTemplates = array(
        self::NOT_MATCH => '机器人阻止'
    );

    public function isValid($value) {
    	$result=bcspamblock_verify();
      return $result;
    }
}

4 创建自定义的form

<?php

class ContactForm extends Zend_Form
{
    public function __construct($options = null)
    {
        parent::__construct($options);
        $this->setName('Contact');

        $username = new Zend_Form_Element_Text('username');
        $username->setLabel('用户名')->setRequired(true)
        ->addFilter('StripTags') ->addFilter('StringTrim')
        ->addValidator('StringLength',false,array(3,50));
        
       
        $email=new Zend_Form_Element_Text('email');
        $email->setLabel('E-Mail')
        			->setRequired(true)
        			->addFilter('StringTrim')
        			->addValidator('NotEmpty')
        			->addValidator('EmailAddress');
		  
		  $subject=new Zend_Form_Element_Text('subject');
		  $subject->setLabel('主题')->setRequired(true);
		  
		  $body=new Zend_Form_Element_Textarea('body');
		  $body->setLabel('内容')->setRequired(true)->setAttrib('rows',4);
		  
        $id = new Zend_Form_Element_Hidden('id');
        
        $submit = new Zend_Form_Element_Submit('submit');
        $submit->setAttrib('id', 'submitbutton')->setLabel('发送');
        
        $spam=new element_bcSpamBlock('spam');
        $spam->addPrefixPath('Validator','validator/','validate')
        		 ->addValidator('SpamBlock');
        

        $this->addElements(array($id, $spam,$username,$email,$subject,$body,$submit));
    }
}

5 在action中调用此form

function contactAction()
    {
    	$form=new ContactForm();
    	$this->view->form=$form;
    	$this->view->addHelperPath('helper','Zend_View_Helper_');
    	if ($this->_request->isPost()) {
    		//发送邮件
    		$formData=$this->_request->getPost();
    		include_once("bcspamblock.php");
    		if (bcspamblock_verify() && $form->isValid($formData)) {
    			$mail=new Zend_Mail('utf-8');
....

因为第3步中的validator自动调用不成功，因此在此进行了手工的判断。