public void addHeaderHolder(ViewHolder viewHolder){
  tryThrowAlreadyBoundException("Cannot bind a header holder post-bind due to limitations of view types and recycling.");
  headerHolders.add(viewHolder);
  onItemRangeInserted(getHeadersCount() - 1,1);
}

public void addHeaderHolder ( ViewHolder viewHolder ) { tryThrowAlreadyBoundException ( "Cannot bind a header holder post-bind due to limitations of view types and recycling." ) ; headerHolders . add ( viewHolder ) ; onItemRangeInserted ( getHeadersCount ( ) - 1 , 1 ) ; }
adds a header to this adapter .
