How to: Use a Custom Converter for Export to a DataTable

• Dec 12, 2022
• 4 minutes to read

The DataTableExportOptions.CustomConverters property enables you to specify a custom converter for a specific DataTable column. To do this, create a class that implements the ICellValueToColumnTypeConverter interface. The ICellValueToColumnTypeConverter.Convert method should perform the required conversion. Subsequently, add an instance of a custom converter to the collection of custom converters available via the DataTableExporter.Options.CustomConverters notation using the Add method.

The Convert method is called for each cell that is exported to the specified column.

The following code snippet illustrates the technique. The converter transforms DateTime values into strings in MMMM-yyyy format, and displays the “N/A” text if a cell contains an error.

View Example

Form1.cs

using DevExpress.Spreadsheet;
using DevExpress.Spreadsheet.Export;
        private void barButtonItemUseCustomConverter_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
        {
            Worksheet worksheet = spreadsheetControl1.Document.Worksheets[0];
            CellRange range = worksheet.Tables[0].Range;

            // Create a data table with column names obtained from the first row in a range.
            // Column data types are obtained from cell value types of cells in the first data row of the worksheet range.
            DataTable dataTable = worksheet.CreateDataTable(range, true);
            // Change the data type of the "As Of" column to text.
            dataTable.Columns["As Of"].DataType = System.Type.GetType("System.String");
            // Create the exporter that obtains data from the specified range and populates the specified data table. 
            DataTableExporter exporter = worksheet.CreateDataTableExporter(range, dataTable, true);
            // Handle value conversion errors.
            exporter.CellValueConversionError += exporter_CellValueConversionError;

            // Specify a custom converter for the "As Of" column.
            DateTimeToStringConverter toDateStringConverter = new DateTimeToStringConverter();
            exporter.Options.CustomConverters.Add("As Of", toDateStringConverter);
            // Set the export value for empty cell.
            toDateStringConverter.EmptyCellValue = "N/A";
            // Specify that empty cells and cells with errors should be processed.
            exporter.Options.ConvertEmptyCells = true;
            exporter.Options.DefaultCellValueToColumnTypeConverter.SkipErrorValues = false;

            // Perform the export.
            exporter.Export();

            // A custom method that displays the resulting data table.
            ShowResult(dataTable);
        }

        // A custom converter that converts DateTime values to "Month-Year" text strings.
        class DateTimeToStringConverter : ICellValueToColumnTypeConverter
        {
            public bool SkipErrorValues { get; set; }
            public CellValue EmptyCellValue { get; set; }

            public ConversionResult Convert(Cell readOnlyCell, CellValue cellValue, Type dataColumnType, out object result)
            {
                result = DBNull.Value; 
                ConversionResult converted = ConversionResult.Success;
                if (cellValue.IsEmpty) {
                    result = EmptyCellValue;
                    return converted;
                }
                if (cellValue.IsError) {
                    // You can return an error, subsequently the exporter throws an exception if the CellValueConversionError event is unhandled.
                    //return SkipErrorValues ? ConversionResult.Success : ConversionResult.Error;
                    result = "N/A";
                    return ConversionResult.Success;
                }
                result =  String.Format("{0:MMMM-yyyy}",cellValue.DateTimeValue);
                return converted;
            }
        }
        void exporter_CellValueConversionError(object sender, CellValueConversionErrorEventArgs e)
        {
            MessageBox.Show("Error in cell " + e.Cell.GetReferenceA1());
            e.DataTableValue = null;
            e.Action = DataTableExporterAction.Continue;
        }

Form1.vb

Imports DevExpress.Spreadsheet
Imports DevExpress.Spreadsheet.Export
        Private Sub barButtonItemUseCustomConverter_ItemClick(ByVal sender As Object, ByVal e As DevExpress.XtraBars.ItemClickEventArgs) Handles barButtonItemUseCustomConverter.ItemClick
            Dim worksheet As Worksheet = spreadsheetControl1.Document.Worksheets(0)
            Dim range As CellRange = worksheet.Tables(0).Range

            ' Create a data table with column names obtained from the first row in a range.
            ' Column data types are obtained from cell value types of cells in the first data row of the worksheet range.
            Dim dataTable As DataTable = worksheet.CreateDataTable(range, True)
            ' Change the data type of the "As Of" column to text.
            dataTable.Columns("As Of").DataType = System.Type.GetType("System.String")
            ' Create the exporter that obtains data from the specified range and populates the specified data table. 
            Dim exporter As DataTableExporter = worksheet.CreateDataTableExporter(range, dataTable, True)
            ' Handle value conversion errors.
            AddHandler exporter.CellValueConversionError, AddressOf exporter_CellValueConversionError

            ' Specify a custom converter for the "As Of" column.
            Dim toDateStringConverter As New DateTimeToStringConverter()
            exporter.Options.CustomConverters.Add("As Of", toDateStringConverter)
            ' Set the export value for empty cell.
            toDateStringConverter.EmptyCellValue = "N/A"
            ' Specify that empty cells and cells with errors should be processed.
            exporter.Options.ConvertEmptyCells = True
            exporter.Options.DefaultCellValueToColumnTypeConverter.SkipErrorValues = False

            ' Perform the export.
            exporter.Export()

            ' A custom method that displays the resulting data table.
            ShowResult(dataTable)
        End Sub

        ' A custom converter that converts DateTime values to "Month-Year" text strings.
        Private Class DateTimeToStringConverter
            Implements ICellValueToColumnTypeConverter

            Public Property SkipErrorValues() As Boolean
            Public Property EmptyCellValue() As CellValue Implements ICellValueToColumnTypeConverter.EmptyCellValue

            Public Function Convert(ByVal readOnlyCell As Cell, ByVal cellValue As CellValue, ByVal dataColumnType As Type, <System.Runtime.InteropServices.Out()> ByRef result As Object) As ConversionResult Implements ICellValueToColumnTypeConverter.Convert
                result = DBNull.Value
                Dim converted As ConversionResult = ConversionResult.Success
                If cellValue.IsEmpty Then
                    result = EmptyCellValue
                    Return converted
                End If
                If cellValue.IsError Then
                    ' You can return an error, subsequently the exporter throws an exception if the CellValueConversionError event is unhandled.
                    'return SkipErrorValues ? ConversionResult.Success : ConversionResult.Error;
                    result = "N/A"
                    Return ConversionResult.Success
                End If
                result = String.Format("{0:MMMM-yyyy}", cellValue.DateTimeValue)
                Return converted
            End Function
        End Class
        Private Sub exporter_CellValueConversionError(ByVal sender As Object, ByVal e As CellValueConversionErrorEventArgs)
            MessageBox.Show("Error in cell " & e.Cell.GetReferenceA1())
            e.DataTableValue = Nothing
            e.Action = DataTableExporterAction.Continue
        End Sub