Android : Download Manager Broadcast Receiver and loop through listview

I have an app with list view of downloadable files. i used Download Manager for handling multiple downloads. Now my problem is i need to update list view row of completed download so in Broadcast Receiver i lop through list view rows to find appropriate row of data and update it but i receive Null pointer Exception in 6th item in list view.

BroadcastReceiver downloadReceiver = new BroadcastReceiver() {

      @Override
      public void onReceive(Context context, Intent intent) {

       long referenceId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);

        final ListView listView = getListView();
        String[] a = null;

        for (int i = 0; i < listView.getCount(); i++) {
            View v = listView.getChildAt(i);
            TextView et = (TextView) v.findViewById(R.id.dmrefrence);
            Log.d( "position",et.getText().toString() );
            Log.d( "i",Integer.toString(i) );
            if(et.getText().toString() == Long.toString(referenceId) ){

                ImageButton cancelButton = (ImageButton) v.findViewById(R.id.cancelButton);
                cancelButton.setVisibility( View.GONE );
            }

        }

      }
};//end of broadcast reciever