Sub SetCellAggregationFormat( _
   ByVal row As Integer, _
   ByVal col As Integer, _
   ByVal format As String _
) 

Dim instance As IAggregationSupport
Dim row As Integer
Dim col As Integer
Dim format As String
 
instance.SetCellAggregationFormat(row, col, format)

void SetCellAggregationFormat( 
   int row,
   int col,
   string format
)

fpSpread1.Sheets[0].RowCount=8;
fpSpread1.Sheets[0].ColumnCount = 15;
fpSpread1.Sheets[0].GroupBarInfo.Visible = true;
fpSpread1.Sheets[0].AllowGroup = true;
fpSpread1.Sheets[0].GroupFooterVisible = true;
fpSpread1.Sheets[0].ColumnFooter.Visible = true;
fpSpread1.Sheets[0].ColumnFooter.RowCount = 2;
fpSpread1.Sheets[0].ColumnFooter.Columns[12].HorizontalAlignment = FarPoint.Win.Spread.CellHorizontalAlignment.Left;
fpSpread1.Sheets[0].ColumnFooter.Cells[0, 12].RowSpan = 2; 
//Value
for (int r = 0; r < fpSpread1.Sheets[0].RowCount; r++)
{
        for (int j = 0; j < fpSpread1.Sheets[0].ColumnCount; j++)
    {
        fpSpread1.Sheets[0].Models.Data.SetValue(r, j, j + r * fpSpread1.Sheets[0].ColumnCount); 
    }
}
int i=0;
fpSpread1.Sheets[0].ColumnFooter.SetAggregationFormat(0, 1, "Sum:{0}");
fpSpread1.Sheets[0].ColumnFooter.SetAggregationType(0,1, FarPoint.Win.Spread.Model.AggregationType.Sum); 
fpSpread1.Sheets[0].Models.ColumnFooterRowAxis.SetResizable(1, true);
fpSpread1.Sheets[0].ColumnFooter.Cells[0, i].Value = "Sum"; 

private void fpSpread1_Grouped(object sender, EventArgs e)
 {
  FarPoint.Win.Spread.Model.GroupDataModel gdm;
  gdm = (FarPoint.Win.Spread.Model.GroupDataModel)fpSpread1.ActiveSheet.Models.Data;
  gdm.GroupFooterVisible = true;
  FarPoint.Win.Spread.Model.Group g1 = (FarPoint.Win.Spread.Model.Group)gdm.Groups[1];           
  ((FarPoint.Win.Spread.Model.IAggregationSupport)g1.GroupFooter.DataModel).SetCellAggregationType(0, 0, FarPoint.Win.Spread.Model.AggregationType.Sum);
((FarPoint.Win.Spread.Model.IAggregationSupport)g1.GroupFooter.DataModel).SetCellAggregationFormat(0, 0, "Sum: {0}");
  fpSpread1.ActiveSheet.Models.Data = gdm;
  }

FpSpread1.Sheets(0).RowCount = 8
FpSpread1.Sheets(0).ColumnCount = 15
FpSpread1.Sheets(0).GroupBarInfo.Visible = True
FpSpread1.Sheets(0).AllowGroup = True
FpSpread1.Sheets(0).GroupFooterVisible = True
FpSpread1.Sheets(0).ColumnFooter.Visible = True
FpSpread1.Sheets(0).ColumnFooter.RowCount = 2
fpSpread1.Sheets(0).ColumnFooter.Columns(12).HorizontalAlignment = FarPoint.Win.Spread.CellHorizontalAlignment.Left
'Value
        Dim r As Integer
        Dim j As Integer
        For r = 0 To FpSpread1.Sheets(0).RowCount
            For j = 0 To FpSpread1.Sheets(0).ColumnCount
                FpSpread1.Sheets(0).Models.Data.SetValue(r, j, j + r * FpSpread1.Sheets(0).ColumnCount)
            Next j
        Next r
        Dim i As Integer
        i = 0
FpSpread1.Sheets(0).ColumnFooter.SetAggregationFormat(0, 1, "Sum:{0}")
FpSpread1.Sheets(0).ColumnFooter.SetAggregationType(0, 1, FarPoint.Win.Spread.Model.AggregationType.Sum)
FpSpread1.Sheets(0).Models.ColumnFooterRowAxis.SetResizable(1, True)
FpSpread1.Sheets(0).ColumnFooter.Cells(0, i).Value = "Sum"

Private Sub FpSpread1_Grouped(ByVal sender As Object, ByVal e As System.EventArgs) Handles FpSpread1.Grouped
        Dim gdm As FarPoint.Win.Spread.Model.GroupDataModel
        Dim g1 As FarPoint.Win.Spread.Model.Group
        gdm = FpSpread1.Sheets(0).Models.Data
        gdm.GroupFooterVisible = True
        g1 = gdm.Groups(1)
        CType(g1.GroupFooter.DataModel, FarPoint.Win.Spread.Model.IAggregationSupport).SetCellAggregationType(0, 0, FarPoint.Win.Spread.Model.AggregationType.Sum)
CType(g1.GroupFooter.DataModel, FarPoint.Win.Spread.Model.IAggregationSupport).SetCellAggregationFormat(0, 0, "Sum: {0}")
        FpSpread1.ActiveSheet.Models.Data = gdm
    End Sub