Unable to add window -- token null is not valid

如果在 onCreate 中创建该问题，就会报如上异常

【如果activity已经finish掉了。在handlerMessage中调用的时候 也会报异常】

解决办法：在onCreate中执行：

 mHandler.sendEmptyMessageDelayed(SHOWWINDOW, 200);  

 private Handler mHandler = new Handler()
  {
    public void handleMessage(Message msg)
    {
      switch (msg.what)
      {
        case SHOWWINDOW:
          popupWindow = new PopupWindow(popView,
            LayoutParams.FILL_PARENT,
            LayoutParams.FILL_PARENT);
          popupWindow.showAtLocation(popView,
            Gravity.BOTTOM,
            0,
            0);
          Log.debug(TAG,
            "init popupWindow and showing!");
          break;
        case ClOSEWINDOW:
          if (popupWindow != null)
          {
            popupWindow.dismiss();
          }
          Log.debug(TAG,
            "close popupWindow and destory!");
          break;
      }
    }


  };