notifyDataSetChanged() not work ?

Question

Hi Friends

i am developing application for view images from gridview using xml parsing and webveiw,initially i show 16 images in gridview ,user can click last images for view that image in webview and back to grid,this time i call Asysntask for parse another 16 images from other url and set adapter and used notifyDataSetChanged() for reload grid and old and new images(total 32 images) in gridview.but i got last 16 images (2nd url) only diplayed in grid view..what can i do`

public void onActivityResult(int requestCode, int resultCode, Intent data)
   {     
       super.onActivityResult(requestCode, resultCode, data); 
       switch(requestCode) { 
       case (0) : { 
           if (resultCode == Activity.RESULT_OK)
           {                         
               if (data != null)
               {
                  Bundle b= data.getExtras();
                   String s= b.getString("name");
                   int pno=b.getInt("pageno");
                    url="http://www.theblacksheeponline.com/partypics.php?page="+pno;
                  new Task_xmlparser().execute(); 
                  g_adp.notifyDataSetChanged();           
               } 
               break; 

           }
       }
       }
   }
`