void OnSelectionChanged(Security security)
 {
     if (security != null)
     {
         TrendGraph graph = (TrendGraph)ServiceProvider.GetService(typeof(TrendGraph));
         if (graph != null)
         {
             UpdateGraph(graph, security);
         }
     }
 }
 private void UpdateGraph(TrendGraph graph, Security security)
 {
     // todo: need to make TrendGraph more general.  It should not know about Transactions directly.
 }