如何使用zend框架制作自定义图像文件格式

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

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);
    }
}
}

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>\';    
}    
}

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

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