unable to add window -- token nu

To avoid BadTokenException, you need to defer showing the popup until after all the lifecycle methods are called (-> activity window is displayed):

findViewById(R.id.main_page_layout).post(new Runnable() {
   public void run() {
     pw.showAtLocation(findViewById(R.id.main_page_layout), Gravity.CENTER, 0, 0);
   }
});