void UpdateAggregates(List <Band> bands)
 {
     foreach (Band band in bands)
     {
         foreach (BaseWidget widget in band.Items)
         {
             ValueWidget vw = widget as ValueWidget;
             if (vw != null && vw.CalcType != CalcEnum.None)
             {
                 vw.Aggregate(GetColumnValue(vw.ColumnName));
             }
         }
     }
 }
 void Update()
 {
     foreach (Band band in _model.Bands)
     {
         foreach (BaseWidget widget in band.Items)
         {
             ValueWidget vw = widget as ValueWidget;
             if (vw != null)
             {
                 object colValue = GetColumnValue(vw.ColumnName);
                 if (vw.CalcType == CalcEnum.None)
                 {
                     vw.SetValue(colValue);
                 }
                 else
                 {
                     vw.Aggregate(colValue);
                 }
             }
         }
     }
 }