How to calculate summaries for both minimum and maximum values of the date field in WinForms GridGroupingControl?

public sealed class DateMaxSummary : SummaryBase
{
    DateTime _max;
    public DateMaxSummary(DateTime max)
    {
        _max = max;
    }
    public static readonly DateMaxSummary Empty = new DateMaxSummary(DateTime.MinValue);
    // Assign this CreateSummaryDelegate handler method to SummaryDescriptor.CreateSummaryMethod
    public static ISummary CreateSummaryMethod(SummaryDescriptor sd, Record record)
    {
        object obj = sd.GetValue(record);
        bool isNull = (obj == null || obj is DBNull);
        if(isNull)
           return Empty;
        else
        {
           DateTime val = Convert.ToDateTime(obj);
           return new DateMaxSummary(val);
        }
    }
    // This will return Max value of this summary
    public DateTime Max
    {
        get
        {
            return _max;
        }
    }
    public override SummaryBase Combine(SummaryBase other)
    {
        return Combine((DateMaxSummary)other);
    }
    // Combines this summary information with another objects summary and returns a new object.
    public DateMaxSummary Combine(DateMaxSummary other)
    {
        // Return the Maximum value
        if(Max > other.Max)
           return new DateMaxSummary(this.Max);
        else
           return new DateMaxSummary(other.Max);
    }
}

Public NotInheritable Class DateMaxSummary
    Inherits SummaryBase
    Private _max As DateTime
    Public Sub New(ByVal max As DateTime)
        _max = max
    End Sub
    Public Shared ReadOnly Empty As New DateMaxSummary(DateTime.MinValue)
        ' Assign this CreateSummaryDelegate handler method to SummaryDescriptor.CreateSummaryMethod
   Public Shared Function CreateSummaryMethod(ByVal sd As SummaryDescriptor, ByVal record As Record) As ISummary
       Dim obj As Object = sd.GetValue(record)
       Dim isNull As Boolean = (obj Is Nothing OrElse TypeOf obj Is DBNull)
       If isNull Then
          Return Empty
       Else
          Dim val As DateTime = Convert.ToDateTime(obj)
          Return New DateMaxSummary(val)
       End If
   End Function
    ' This will return Max value of this summary
    Public ReadOnly Property Max() As DateTime
        Get
            Return _max
        End Get
    End Property
    Public Overrides Function Combine(ByVal other As SummaryBase) As SummaryBase
        Return Combine(CType(other, DateMaxSummary))
    End Function
    ' Combines this summary information with another objects summary and returns a new object.
    Public Function Combine(ByVal other As DateMaxSummary) As DateMaxSummary
        ' Return the Maximum value
        If Max > other.Max Then
           Return New DateMaxSummary(Me.Max)
        Else
           Return New DateMaxSummary(other.Max)
        End If
    End Function
End Class

GridSummaryColumnDescriptor sd1 = new GridSummaryColumnDescriptor();
sd1.Name = "MaxDate";
sd1.DataMember = "Date";
sd1.DisplayColumn = "Date";
sd1.Format = "{Max}";
sd1.SummaryType = SummaryType.Custom;
//Adding the Custom Summary rows
this.gridGroupingControl1.TableDescriptor.SummaryRows.Add(new GridSummaryRowDescriptor("Row 1", "Max", sd1));

Dim sd1 As New GridSummaryColumnDescriptor()
sd1.Name = "MaxDate"
sd1.DataMember = "Date"
sd1.DisplayColumn = "Date"
sd1.Format = "{Max}"
sd1.SummaryType = SummaryType.Custom
'Adding the Custom Summary rows
Me.gridGroupingControl1.TableDescriptor.SummaryRows.Add(New GridSummaryRowDescriptor("Row 1", "Max", sd1))

//Hook the QueryCustomSummary event In Form_Load to create summary method while adding the CustomSummary
this.gridGroupingControl1.QueryCustomSummary += gridGroupingControl1_QueryCustomSummary;
private void gridGroupingControl1_QueryCustomSummary(object sender, GridQueryCustomSummaryEventArgs e)
{
   switch (e.SummaryColumn.Name)
   {
      case "MaxDate":
              {
                   e.SummaryDescriptor.CreateSummaryMethod = new CreateSummaryDelegate(DateMaxSummary.CreateSummaryMethod);
                   break;
              }
      case "MinDate":
              {
                   e.SummaryDescriptor.CreateSummaryMethod = new CreateSummaryDelegate(DateMinSummary.CreateSummaryMethod);
                   break;
              }
    }
}

'Hook the QueryCustomSummary event In Form_Load to create summary method while adding the CustomSummary
Private Me.gridGroupingControl1.QueryCustomSummary += AddressOf gridGroupingControl1_QueryCustomSummary
Private Sub gridGroupingControl1_QueryCustomSummary(ByVal sender As Object, ByVal e As GridQueryCustomSummaryEventArgs)
   Select Case e.SummaryColumn.Name
       Case "MaxDate"
               e.SummaryDescriptor.CreateSummaryMethod = New CreateSummaryDelegate(DateMaxSummary.CreateSummaryMethod)
               Exit Select
       Case "MinDate"
               e.SummaryDescriptor.CreateSummaryMethod = New CreateSummaryDelegate(DateMinSummary.CreateSummaryMethod)
               Exit Select
   End Select
End Sub

//Hook the event in Form_Load
this.gridGroupingControl1.CurrentRecordContextChange += gridGroupingControl1_CurrentRecordContextChange;
private void gridGroupingControl1_CurrentRecordContextChange(object sender, CurrentRecordContextChangeEventArgs e)
{
   if(e.Action == CurrentRecordAction.EndEditComplete)
   {
      //Invalidate the Record to Update Summary Values
      e.Record.InvalidateCounterBottomUp();
      this.gridGroupingControl1.Refresh();
   }
}

'Hook the event in Form_Load
Private Me.gridGroupingControl1.CurrentRecordContextChange += AddressOf gridGroupingControl1_CurrentRecordContextChange
Private Sub gridGroupingControl1_CurrentRecordContextChange(ByVal sender As Object, ByVal e As CurrentRecordContextChangeEventArgs)
   If e.Action = CurrentRecordAction.EndEditComplete Then
      'Invalidate the Record to Update Summary Values
      e.Record.InvalidateCounterBottomUp()
      Me.gridGroupingControl1.Refresh()
   End If
End Sub