How to show the sum of two column values in a summary in WinForms GridGroupingControl?

//Sum of col2 and Col3
GridSummaryColumnDescriptor sumCol2 = GetSumSummaryColumnDescriptor("SampleData1", "SampleData2");
GridSummaryRowDescriptor rowDescriptor = new GridSummaryRowDescriptor("Row0", "Sum of SampleData1 and SampleData2 columns", new GridSummaryColumnDescriptor[] { sumCol2 });
this.gridGroupingControl1.TableDescriptor.SummaryRows.Add(rowDescriptor);

/// <summary>
/// Creating a CustomSummaary method.
/// </summary>
private void gridGroupingControl1_QueryCustomSummary(object sender, GridQueryCustomSummaryEventArgs e)
{
    if (e.SummaryDescriptor.SummaryType == SummaryType.Custom)
    {
        e.SummaryDescriptor.CreateSummaryMethod =
            new CreateSummaryDelegate(CustomSummary.CreateSummaryMethod);
    }
    e.Handled = true;
}

/// <summary>
/// Applying WeightedSummary for Given Columns
/// </summary>
private GridSummaryColumnDescriptor GetSumSummaryColumnDescriptor(string col1, string col2)
{
    GridSummaryColumnDescriptor col2Summary = new GridSummaryColumnDescriptor();
    col2Summary.Name = string.Format("{0}_{1}", col1, col2); //special name following the convention above
    col2Summary.DataMember = col1; //the column this summary is applied to
    col2Summary.DisplayColumn = col1; //where this summary is displayed
    col2Summary.Format = "{TotalSummary:#.##}"; //what is displayed in the summary
    col2Summary.SummaryType = SummaryType.Custom; //marks this as a CustomSummary
    col2Summary.Appearance.AnySummaryCell.HorizontalAlignment = GridHorizontalAlignment.Right;
    col2Summary.MaxLength = 6;
    return col2Summary;
}

' Sum of col2 and col3
Dim sumCol2 As GridSummaryColumnDescriptor = GetSumSummaryColumnDescriptor("SampleData1", "SampleData2")
Dim rowDescriptor As New GridSummaryRowDescriptor("Row0", "Sum of SampleData1 and SampleData2 columns", New GridSummaryColumnDescriptor() {sumCol2})
Me.gridGroupingControl1.TableDescriptor.SummaryRows.Add(rowDescriptor)

''' <summary>
''' Creating a CustomSummaary method.
''' </summary>
Private Sub gridGroupingControl1_QueryCustomSummary(ByVal sender As Object, ByVal e As GridQueryCustomSummaryEventArgs)
    If e.SummaryDescriptor.SummaryType = SummaryType.Custom Then
        e.SummaryDescriptor.CreateSummaryMethod = New CreateSummaryDelegate(AddressOf CustomSummary.CreateSummaryMethod)
    End If
    e.Handled = True
End Sub

''' <summary>
''' Applying WeightedSummary for Given Columns
''' </summary>
Private Function GetSumSummaryColumnDescriptor(ByVal col1 As String, ByVal col2 As String) As GridSummaryColumnDescriptor
    Dim col2Summary As New GridSummaryColumnDescriptor()
    col2Summary.Name = String.Format("{0}_{1}", col1, col2) ' special name following the convention above
    col2Summary.DataMember = col1 ' the column this summary is applied to
    col2Summary.DisplayColumn = col1 ' where this summary is displayed
    col2Summary.Format = "{TotalSummary:#.##}" ' what is displayed in the summary
    col2Summary.SummaryType = SummaryType.Custom ' marks this as a CustomSummary
    col2Summary.Appearance.AnySummaryCell.HorizontalAlignment = GridHorizontalAlignment.Right
    col2Summary.MaxLength = 6
    Return col2Summary
End Function

/// <summary>
/// Syncfusion Custom Summary class that computes the weighted average of the of entries 
/// where the weights come in from a column passed in through a naming convention. 
/// </summary>
public sealed class CustomSummary : SummaryBase
{
    #region "API Definition"

    double _valTotal;
    double _wgtTotal;
    public static readonly CustomSummary Empty = new CustomSummary(0, 0);

    #endregion

    #region Constructor
    public CustomSummary()
    {

    }

    /// <summary>
    /// Initializes a new summary object.
    /// </summary>
    /// <param name="valTotal"></param>
    /// <param name="wgtTotal"></param>
    public CustomSummary(double valTotal, double wgtTotal)
    {
        _wgtTotal = wgtTotal;
        _valTotal = valTotal;
    }

    #endregion

    #region CreateSummaryMethod
    /// <summary>
    /// Assign this CreateSummaryDelegate handler method to SummaryDescriptor.CreateSummaryMethod 
    /// </summary>
    /// <param name="sd"></param>
    /// <param name="record"></param>
    /// <returns></returns>
    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
        {
            int i = sd.Name.LastIndexOf('_') + 1;
            string col2 = sd.Name.Substring(i);
            object obj1 = record.GetValue(col2);
            if (obj1 == null)
            {
                throw new ArgumentException(string.Format("[{0}] not a column.", col2));
            }

            double col2Value = Convert.ToDouble(obj1);
            double col1 = Convert.ToDouble(obj);

            return new CustomSummary(col1, col2Value);
        }
    }

    #endregion

    #region "Weighted Summary Calculation"        
    /// <summary>
    /// The running weighted sum of this summary
    /// </summary>
    public double TotalSummary
    {
        get
        {
            if (_wgtTotal == 0)
                return _wgtTotal;
            return _valTotal + _wgtTotal;
        }
    }

    /// <summary>
    /// Combines this summary information with another objects summary and returns a new object.  
    /// </summary>
    /// <param name="other"></param>
    /// <returns></returns>
    /// <remarks>
    /// This method must honor the immutable characteristics of summary objects and return 
    /// a new summary object instead of modifying an existing summary object.
    /// </remarks>
    public override SummaryBase Combine(SummaryBase other)
    {
        return Combine((CustomSummary)other);
    }

    /// <summary>
    /// Combines this summary information with another objects summary and returns a new object.  
    /// </summary>
    /// <remarks>
    /// This method must honor the immutable characteristics of summary objects and return 
    /// a new summary object instead of modifying an existing summary object.
    /// </remarks>
    public CustomSummary Combine(CustomSummary other)
    {
        // Summary objects are immutable. That means properties cannot be modified for an 
        // existing object. Instead every time a change is made a new object must be created (just like 
        // System.String). 
        return new CustomSummary(this._valTotal + other._valTotal, this._wgtTotal + other._wgtTotal);
    }

    /// <override/>
    public override string ToString()
    {
        return String.Format("TotalSummary = {0:0.00}", TotalSummary);
    }
    #endregion
}

''' <summary>
''' Syncfusion Custom Summary class that computes the weighted average of the of entries 
''' where the weights come in from a column passed in through a naming convention. 
''' </summary>
Public NotInheritable Class CustomSummary
    Inherits SummaryBase
#Region "API Definition"

    Private _valTotal As Double
    Private _wgtTotal As Double
    Public Shared ReadOnly Empty As New CustomSummary(0, 0)

#End Region

#Region "Constructor"
    Public Sub New()
    End Sub
    ''' <summary>
    ''' Initializes a new summary object.
    ''' </summary>
    ''' <param name="valTotal"></param>
    ''' <param name="wgtTotal"></param>
    Public Sub New(ByVal valTotal As Double, ByVal wgtTotal As Double)
        _wgtTotal = wgtTotal
        _valTotal = valTotal
    End Sub

#End Region

#Region "CreateSummaryMethod"
    ''' <summary>
    ''' Assign this CreateSummaryDelegate handler method to SummaryDescriptor.CreateSummaryMethod 
    ''' </summary>
    ''' <param name="sd"></param>
    ''' <param name="record"></param>
    ''' <returns></returns>
    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 i As Integer = sd.Name.LastIndexOf("_"c) + 1
            Dim col2 As String = sd.Name.Substring(i)
            Dim obj1 As Object = record.GetValue(col2)
            If obj1 Is Nothing Then
                Throw New ArgumentException(String.Format("[{0}] not a column.", col2))
            End If

            Dim col2Value As Double = Convert.ToDouble(obj1)
            Dim col1 As Double = Convert.ToDouble(obj)
            Return New CustomSummary(col1, col2Value)
        End If
    End Function

#End Region

#Region "Weighted Summary Calculation"
    ''' <summary>
    ''' The running weighted sum of this summary
    ''' </summary>
    Public ReadOnly Property TotalSummary() As Double
        Get
            If _wgtTotal = 0 Then
                Return _wgtTotal
            End If
            Return _valTotal + _wgtTotal
        End Get
    End Property

    ''' <summary>
    ''' Combines this summary information with another objects summary and returns a new object.  
    ''' </summary>
    ''' <param name="other"></param>
    ''' <returns></returns>
    ''' <remarks>
    ''' This method must honor the immutable characteristics of summary objects and return 
    ''' a new summary object instead of modifying an existing summary object.
    ''' </remarks>
    Public Overrides Function Combine(ByVal other As SummaryBase) As SummaryBase
        Return Combine(CType(other, CustomSummary))
    End Function

    ''' <summary>
    ''' Combines this summary information with another objects summary and returns a new object.  
    ''' </summary>
    ''' <remarks>
    ''' This method must honor the immutable characteristics of summary objects and return 
    ''' a new summary object instead of modifying an existing summary object.
    ''' </remarks>
    Public Function Combine(ByVal other As CustomSummary) As CustomSummary
        ' Summary objects are immutable. That means properties cannot be modified for an 
        ' existing object. Instead every time a change is made a new object must be created (just like 
        ' System.String).   
        Return New CustomSummary(Me._valTotal + other._valTotal, Me._wgtTotal + other._wgtTotal)
    End Function

    ''' <override/>
    Public Overrides Function ToString() As String
        Return String.Format("TotalSummary = {0:0.00}", TotalSummary)
    End Function
#End Region
End Class