public void ReportError(object commandId, string message, Exception ex)
 {
     if (CommandError != null) {
         CommandErrorArgs args = new CommandErrorArgs (commandId, message, ex);
         CommandError (this, args);
     }
 }
 void OnCommandError(object sender, CommandErrorArgs args)
 {
     Runtime.MessageService.ShowError (args.Exception, args.ErrorMessage);
 }