严格的标准错误，无法解决

我尝试过，但无法解决，已检查并在严格标准上得到错误

严格的标准：在…中只有变量应该通过引用传递。。。

我做错了什么-如何纠正

$this->assignRef('prodDet'  , $prodDet);
$this->assignRef('CatName'  , $modelNewcar->getCatName($id));
$this->assignRef('nav'  , $nav);
$this->assignRef('CatList'  , $modelNewcar->loadMainCat($brand,$Carmodel,$minprice,$maxprice,$fuel_type));
    $this->assignRef('CatName'  , $modelNewcar->getCatName);
parent::display($tpl);

下面是原始代码

function display($tpl = null)
{
    $mainframe =JFactory::getApplication();
    $option = JRequest::getCmd('option');
    $db         =JFactory::getDBO();
    $user               = JFactory::getUser();
    // Push a model into the view
    $model              = $this->getModel();
    $modelNewcar    = $this->getModel( 'product' );
    $id = JRequest::getVar('id','','default','int');
    $vid = JRequest::getVar('vid','','default','int');
    $prodDet = $modelNewcar->loadProduct($id,$vid);
    $this->assignRef('prodDet'  , $prodDet);
    $this->assignRef('CatName'  , $modelNewcar->getCatName($id));
    parent::display($tpl);
}
 function display($tpl = null)
{
    $db =JFactory::getDBO();
    $user               = JFactory::getUser();
    // Push a model into the view
    $model              =$this->getModel();
    $modelNewcar    =$this->getModel( 'category' );
    $brand = JRequest::getVar('brand','','default','int');
    $Carmodel = JRequest::getVar('model','','default','int');
    $minprice = JRequest::getVar('minprice','','default','int');
    $maxprice = JRequest::getVar('maxprice','','default','int');
    $fuel_type = JRequest::getVar('fuel_type','','default','');

        $this->assignRef('nav'  , $nav);
    $this->assignRef('CatList'  , $modelNewcar->loadMainCat($brand,$Carmodel,$minprice,$maxprice,$fuel_type));
        $this->assignRef('CatName'  , $modelNewcar->getCatName);
    parent::display($tpl);
}