为什么产品没有从这段代码中显示出来？

Question

我在php文件中有这段代码，但是在相应的phtml文件上调用这个函数我得不到产品的结果。我认为这个getOnSaleProduct（）函数不会返回任何内容。请帮助!!

<?php
class VJTemplates_OnSaleVertCarousel_Block_Product_OnSale extends       Mage_Catalog_Block_Product_List {

public function getOnSaleProduct()
{

   $product = Mage::getModel('catalog/product');
   $storeId = Mage::app()->getStore()->getId();
   $collection = $product->getCollection()
    ->addStoreFilter($storeId)
    ->addAttributeToSelect(Mage::getSingleton('catalog/config')->getProductAttributes())
    ->addMinimalPrice()
    ->addFinalPrice()
    ->addTaxPercents()
    ->addAttributeToSelect('name')
    ->addAttributeToSelect('price')
    ->addAttributeToSelect('small_image')
    ->addAttributeToFilter('status',         Mage_Catalog_Model_Product_Status::STATUS_ENABLED)
    ->addAttributeToFilter('visibility',    Mage_Catalog_Model_Product_Visibility::VISIBILITY_BOTH)
    ->addAttributeToFilter("special_from_date", array("date" => true, "to" => date("m/d/y")))
    ->addAttributeToFilter("special_to_date", array("or"=> array(
        0 => array("date" => true, "from" => mktime(0, 0, 0, date("m"), date("d")+1, date("y"))),
        1 => array("is" => new Zend_Db_Expr("null")))
        ), "left");

   if($this->getCategoryId()) 
   {
     $CategoryIds = explode(',',$this->getCategoryId());
     foreach($CategoryIds as $CategoryId) {
        $category = Mage::getModel('catalog/category')->load($CategoryId);
        $category->setIsAnchor(1);
        $collection->addCategoryFilter($category);
     }
   }  

   $currentCategory = Mage::getModel('catalog/layer')->getCurrentCategory()->getId();
   $current_category = Mage::getModel('catalog/category')->load($currentCategory );
   $current_category->setIsAnchor(1);
   $collection->addCategoryFilter($current_category);

   if($this->getOrderby()) $collection->getSelect()->order($this->getOrderby());
   if($this->getNumProducts()) $collection->getSelect()->limit($this->getNumProducts());

   return $collection;

}
}

?>