framework/data/Sort.php
public function getAttributeOrder($attribute)
    {
        $orders = $this->getAttributeOrders();

        return isset($orders[$attribute]) ? $orders[$attribute] : null;
    }
public function getAttributeOrder($attribute)
    {
        $orders = $this->getAttributeOrders();

        return isset($orders[$attribute]) ? $orders[$attribute] : null;
    }
Returns the sort direction of the specified attribute in the current request.
@param string $attribute the attribute name
@return bool|null Sort direction of the attribute. Can be either `SORT_ASC`
for ascending order or `SORT_DESC` for descending order. Null is returned
if the attribute is invalid or does not need to be sorted.