lose filter in pager ,mvc

Question

I have search with dropdownlist , and I have PagedListPager

 

when I request page 2, the value of search still exist, but the value of dropdownlist I lost the selected value of dropdown list

 

I get the value from the URL like this

 

String KEYWORD_NAME = Request.QueryString["Contant.KEYWORD_NAME"];

 

in the first time the KEYWORD_NAME has value but on second page no value while the URL still have the value of"Contant.KEYWORD_NAME "

 

some part of the controller

 

public ActionResult search(int? page, string search )

{

if (search == null )

{

Bindkeyword();

Bindcomany();

return View();

}

else

{

String KEYWORD_NAME = Request.QueryString["Contant.KEYWORD_NAME"];