如何使用zend框架制作自定义图像文件表单

如何通过扩展zend表单元素来创建自定义图像文件？html中的输出如下：

<div class="image-file-wrapper">
     <img src="yourimagepath" />
     <br />
     <input id="image-file" name="image-file" type="file" />
</div>

更新：

我的自定义表单元素

class Engine_Form_Element_ImageFile extends Zend_Form_Element_File {
public $helper = 'FormImageFile';
protected $_image;
public function setImage($src) {
    $this->_image = $src;
    return $this;    
}
public function loadDefaultDecorators() {
    if($this->loadDefaultDecoratorsIsDisabled()) {
        return;
    }
    $decorators = $this->getDecorators();
    if(empty($decorators)) {
        $this->addDecorator('ViewHelper');
        Engine_Form::addDefaultDecorators($this);
    }
}
}

我的自定义视图助手：

class Engine_View_Helper_FormImageFile extends Zend_View_Helper_FormElement {
public function formImageFile($name, $value = null, $attribs = null, $options = null) {
    return '<div class="image-file-wrapper"><img src="test.png" /><input type="file" /></div>';    
}    
}

当我尝试添加它时，

$this->addElement('ImageFile', 'imageFile', array('label' => 'Test Image'));

出现错误：

Warning: Exception caught by form: No file decorator found... unable to render file element Stack Trace: #0 C:'xampp'htdocs'NEOBBS_v6'library'Zend'Form'Decorator'FormElements.php(101): Zend_Form_Element_File->render() #1 C:'xampp'htdocs'NEOBBS_v6'library'Zend'Form.php(2904): Zend_Form_Decorator_FormElements->render('') #2 C:'xampp'htdocs'NEOBBS_v6'library'Zend'Form.php(2920): Zend_Form->render() #3 C:'xampp'htdocs'NEOBBS_v6'application'themes'admin'settings.phtml(8): Zend_Form->__toString() #4 C:'xampp'htdocs'NEOBBS_v6'library'Zend'View.php(108): include('C:'xampp'htdocs...') #5 C:'xampp'htdocs'NEOBBS_v6'library'Zend'View'Abstract.php(880): Zend_View->_run('C:'xampp'htdocs...') #6 C:'xampp'htdocs'NEOBBS_v6'library'Zend'Controller'Action'Helper'ViewRenderer.php(897): Zend_View_Abstract->render('settings.phtml') #7 C:'xampp'htdocs'NEOBBS_v6'library'Zend'Controller'Action.php(243): Zend_Controller_Action_Helper_ViewRenderer->renderScript('settings.phtml', NULL) #8 C:'xampp'htdocs'NEOBBS_v6'application'modules'admin'contr in C:'xampp'htdocs'NEOBBS_v6'library'Zend'Form.php on line 2925

我该怎么修？

提前感谢

Brian