问如何在magento admin近重置过滤器按钮中添加自定义选择字段

EN

public function getMainButtonsHtml() {
    $html = parent::getMainButtonsHtml();
    $add_artwork_button = $this->getLayout()->createBlock('adminhtml/widget_button')
        ->setData(array(
            'label'     => Mage::helper('adminhtml')->__('Add artwork to contract'),
            'onclick'   => 'javascript:openArtworks();',
            'class'   => 'save'
        ));
    $html .= $add_artwork_button->toHtml();
    return $html;
}