Php Magento-adminhtml-下拉列表作为自定义网格上的过滤器

我已经在管理面板中创建了一个自定义订单网格，显示了订单的付款方式和发货方式

以下是我的自定义Grid.php：

<?PHP
class Mage_Adminhtml_Block_Sales_Order_Grid extends

 Mage_Adminhtml_Block_Widget_Grid
{

    public function __construct()
    {
        parent::__construct();
        $this->setId('sales_order_grid');
        $this->setUseAjax(true);
        $this->setDefaultSort('created_at');
        $this->setDefaultDir('DESC');
        $this->setSaveParametersInSession(true);
    }

    /**
     * Retrieve collection class
     *
     * @return string
     */
    protected function _getCollectionClass()
    {
        return 'sales/order_grid_collection';
    }

    protected function _prepareCollection()
    {
        $collection = Mage::getResourceModel($this->_getCollectionClass());
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }

    protected function _prepareColumns()
    {

        $this->addColumn('real_order_id', array(
            'header'=> Mage::helper('sales')->__('Order #'),
            'width' => '80px',
            'type'  => 'text',
            'index' => 'increment_id',
        ));

        if (!Mage::app()->isSingleStoreMode()) {
            $this->addColumn('store_id', array(
                'header'    => Mage::helper('sales')->__('Purchased From (Store)'),
                'index'     => 'store_id',
                'type'      => 'store',
                'store_view'=> true,
                'display_deleted' => true,
            ));
        }

        $this->addColumn('created_at', array(
            'header' => Mage::helper('sales')->__('Purchased On'),
            'index' => 'created_at',
            'type' => 'datetime',
            'width' => '100px',
        ));

        $this->addColumn('billing_name', array(
            'header' => Mage::helper('sales')->__('Клиент'),
            'index' => 'billing_name',
        ));

        $this->addColumn('grand_totals', array(
            'header' => Mage::helper('sales')->__('Авансово плащане'),
            'index' => 'increment_id',
            'width' => '100px',         
            'renderer'  => 'Mage_Adminhtml_Block_Sales_Order_AvansRenderer',
        )); 

        $this->addColumn('avans', array(
            'header' => Mage::helper('sales')->__('Плащане при доставка'),
            'index' => 'increment_id',
            'width' => '50px',          
            'renderer'  => 'Mage_Adminhtml_Block_Sales_Order_BeforeDelRenderer',
        ));

        $this->addColumn('grand_total', array(
            'header' => Mage::helper('sales')->__('Тотал'),
            'index' => 'increment_id',
            'width' => '100px',         
            'renderer'  => 'Mage_Adminhtml_Block_Sales_Order_TotalRenderer',
        ));     

        $this->addColumn('shipping_description', array(
            'header' => Mage::helper('sales')->__('Начин на доставка'),
            'index' => 'shipping_description',
        ));

        $this->addColumn('payment_method',
            array(
                'header'=> Mage::helper('catalog')->__('Начин на плащане'),
                'width' => '230px',
                'index' => 'method',
                'renderer'  => 'Mage_Adminhtml_Block_Catalog_Product_PaymentMethodRenderer',
        ));     
        $this->addColumn('shipping_description', array(
            'header' => Mage::helper('sales')->__('Начин на доставка'),
            'index' => 'shipping_description',
        ));



        $this->addColumn('status', array(
            'header' => Mage::helper('sales')->__('Status'),
            'index' => 'status',
            'type'  => 'options',
            'width' => '70px',
            'options' => Mage::getSingleton('sales/order_config')->getStatuses(),
        ));

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/view')) {
            $this->addColumn('action',
                array(
                    'header'    => Mage::helper('sales')->__('Action'),
                    'width'     => '50px',
                    'type'      => 'action',
                    'getter'     => 'getId',
                    'actions'   => array(
                        array(
                            'caption' => Mage::helper('sales')->__('View'),
                            'url'     => array('base'=>'*/sales_order/view'),
                            'field'   => 'order_id',
                            'data-column' => 'action',
                        )
                    ),
                    'filter'    => false,
                    'sortable'  => false,
                    'index'     => 'stores',
                    'is_system' => true,
            ));
        }
        $this->addRssList('rss/order/new', Mage::helper('sales')->__('New Order RSS'));

        $this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV'));
        $this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel XML'));

        return parent::_prepareColumns();
    }

    protected function _prepareMassaction()
    {
        $this->setMassactionIdField('entity_id');
        $this->getMassactionBlock()->setFormFieldName('order_ids');
        $this->getMassactionBlock()->setUseSelectAll(false);

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/cancel')) {
            $this->getMassactionBlock()->addItem('cancel_order', array(
                 'label'=> Mage::helper('sales')->__('Cancel'),
                 'url'  => $this->getUrl('*/sales_order/massCancel'),
            ));
        }

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/hold')) {
            $this->getMassactionBlock()->addItem('hold_order', array(
                 'label'=> Mage::helper('sales')->__('Hold'),
                 'url'  => $this->getUrl('*/sales_order/massHold'),
            ));
        }

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/unhold')) {
            $this->getMassactionBlock()->addItem('unhold_order', array(
                 'label'=> Mage::helper('sales')->__('Unhold'),
                 'url'  => $this->getUrl('*/sales_order/massUnhold'),
            ));
        }

        $this->getMassactionBlock()->addItem('pdfinvoices_order', array(
             'label'=> Mage::helper('sales')->__('Print Invoices'),
             'url'  => $this->getUrl('*/sales_order/pdfinvoices'),
        ));

        $this->getMassactionBlock()->addItem('pdfshipments_order', array(
             'label'=> Mage::helper('sales')->__('Print Packingslips'),
             'url'  => $this->getUrl('*/sales_order/pdfshipments'),
        ));

        $this->getMassactionBlock()->addItem('pdfcreditmemos_order', array(
             'label'=> Mage::helper('sales')->__('Print Credit Memos'),
             'url'  => $this->getUrl('*/sales_order/pdfcreditmemos'),
        ));

        $this->getMassactionBlock()->addItem('pdfdocs_order', array(
             'label'=> Mage::helper('sales')->__('Print All'),
             'url'  => $this->getUrl('*/sales_order/pdfdocs'),
        ));

        $this->getMassactionBlock()->addItem('print_shipping_label', array(
             'label'=> Mage::helper('sales')->__('Print Shipping Labels'),
             'url'  => $this->getUrl('*/sales_order_shipment/massPrintShippingLabel'),
        ));

        return $this;
    }

    public function getRowUrl($row)
    {
        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/view')) {
            return $this->getUrl('*/sales_order/view', array('order_id' => $row->getId()));
        }
        return false;
    }

    public function getGridUrl()
    {
        return $this->getUrl('*/*/grid', array('_current'=>true));
    }

}