title: android.view.WindowManager$BadTokenException: Unable to add window — token null is not valid
body: <p>I get this error whenever I try to start my window class. I am using separate class, and not just a method within my game class, cause I need to disable back button on that popup window. I am calling this class with a button. This code works fine if I use it within my game class, but not in separate class. Here is my code:</p>
  
  <pre><code>public class Popup_pogresno extends Activity implements OnClickListener{
  
      private PopupWindow pwindow;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          // TODO Auto-generated method stub
          super.onCreate(savedInstanceState);
  
          LayoutInflater layoutInflater 
           = (LayoutInflater)Popup_pogresno.this
            .getSystemService(LAYOUT_INFLATER_SERVICE);  
          View popupView = layoutInflater.inflate(R.layout.popup, null);  
                   pwindow  = new PopupWindow(popupView, 300, 170, true);
  
                   Button btnDismiss = (Button)popupView.findViewById(R.id.bPopupOK);
                   btnDismiss.setOnClickListener(new Button.OnClickListener(){
  
           public void onClick(View v) {
            // TODO Auto-generated method stub
               pwindow.dismiss();
           }});
  
                   pwindow.showAtLocation(popupView, Gravity.CENTER, 0, 0);
  
         }
  
      public void onClick(View v) {
          // TODO Auto-generated method stub
  
      }
      @Override
      public void onBackPressed() {
  
      }
  }
  </code></pre>