public event ASPxGridViewColumnDataEventHandler CustomUnboundColumnData

Public Event CustomUnboundColumnData As ASPxGridViewColumnDataEventHandler

<dx:ASPxGridView ID="Grid" ClientInstanceName="Grid" runat="server" AutoGenerateColumns="false"
        DataSourceID="ProductsDataSource" KeyFieldName="OrderID" OnInit="Grid_Init" OnCustomUnboundColumnData="Grid_CustomUnboundColumnData">
        <SettingsPager PageSize="5" />
        <Columns>
            <dx:GridViewDataTextColumn FieldName="ProductName" />
            <dx:GridViewDataSpinEditColumn FieldName="UnitPrice" >
                <PropertiesSpinEdit DisplayFormatString="c" DecimalPlaces="2" />
            </dx:GridViewDataSpinEditColumn>
            <dx:GridViewDataSpinEditColumn FieldName="Quantity" >
            </dx:GridViewDataSpinEditColumn>
            <dx:GridViewDataSpinEditColumn FieldName="Discount" >
                <PropertiesSpinEdit DisplayFormatString="p0"></PropertiesSpinEdit>
            </dx:GridViewDataSpinEditColumn>
        </Columns>
</dx:ASPxGridView>
<ef:EntityDataSource runat="server" ID="ProductsDataSource" ContextTypeName="DevExpress.Web.Demos.NorthwindContext" EntitySetName="Invoices" />

using DevExpress.Web.ASPxGridView;

protected void Grid_Init(object sender, EventArgs e) {
    // Creates a column, customizes its settings, and appends it to the Columns collection.
    GridViewDataTextColumn colTotal = new GridViewDataTextColumn();
    colTotal.FieldName = "Total";
    colTotal.UnboundType = DevExpress.Data.UnboundColumnType.Decimal;
    colTotal.VisibleIndex = Grid.VisibleColumns.Count;
    colTotal.PropertiesTextEdit.DisplayFormatString = "c2";
    Grid.Columns.Add(colTotal);
}
// Populates the unbound column.
protected void Grid_CustomUnboundColumnData(object sender,
    ASPxGridViewColumnDataEventArgs e) {
    if (e.Column.FieldName == "Total") {
        decimal unitPrice = Convert.ToDecimal(e.GetListSourceFieldValue("UnitPrice"));
        int quantity = Convert.ToInt32(e.GetListSourceFieldValue("Quantity"));
        decimal discount = Convert.ToDecimal(e.GetListSourceFieldValue("Discount"));
        e.Value = unitPrice * quantity * (1 - discount);
    }
}

Imports DevExpress.Web.ASPxGridView

Protected Sub Grid_Init(ByVal sender As Object, ByVal e As System.EventArgs)_
    Handles Grid.Init
    ' Creates a column, customizes its settings, and appends it to the Columns collection.
    Dim colTotal As GridViewDataTextColumn = New GridViewDataTextColumn()
    colTotal.FieldName = "Total"
    colTotal.UnboundType = DevExpress.Data.UnboundColumnType.Decimal
    colTotal.VisibleIndex = Grid.VisibleColumns.Count
    colTotal.PropertiesTextEdit.DisplayFormatString = "c2"
    Grid.Columns.Add(colTotal)
End Sub

' Populates the unbound column.
Protected Sub Grid_CustomUnboundColumnData(ByVal sender As Object,_
   ByVal e As DevExpress.Web.ASPxGridViewColumnDataEventArgs)_
    Handles Grid.CustomUnboundColumnData
    If e.Column.FieldName = "Total" Then
        Dim unitPrice As Decimal = Convert.ToDecimal(e.GetListSourceFieldValue("UnitPrice"))
        Dim quantity As Integer = Convert.ToInt32(e.GetListSourceFieldValue("Quantity"))
        Dim discount As Decimal = Convert.ToDecimal(e.GetListSourceFieldValue("Discount"))
        e.Value = unitPrice * quantity * (1 - discount)
    End If
End Sub