在專案中, 因為要保存格式, 故用cell的dataformat 進行轉換, 若轉換不到才用回原本的CellNumericValue. 部份程式碼如下:

 // NPOI issue, it will calculate value in double format, so need to change in string format with cell data format and convert back to double.
                                                // Append below if any specif char. found.
                                                double castValue;
                                                bool castResult=  double.TryParse(cell.NumericCellValue.ToString(cell.CellStyle.GetDataFormatString())
                                                    .Replace(",", "")
                                                    .Replace("_", "")
                                                    .Replace("(", "")
                                                    .Replace(")", "")
                                                    .Replace("$", "")
                                                    , out castValue);
                                                if (castResult == false)
                                                    castValue = cell.NumericCellValue;
                                                dr[i] = castValue;

ExcelHelper.cs

 public class ExcelHelper
    {
public DataTable readExcelToDataTable(string filePath, int sheetNum, int headerLine, int contentLine)
        {
            this.loadExcelFile(filePath);
            this.resetCurrentDataTable();
            this.readExcelHeader(sheetNum, headerLine, contentLine);
            return this.readExcelData(sheetNum, contentLine);     //line 0 is header, data start from line 1
        }
 public void loadExcelFile(string filePath)
        {
            using (FileStream file = new FileStream(filePath, FileMode.Open, FileAccess.Read))
            {
                currentExcelFileType = Path.GetExtension(filePath);

                if (currentExcelFileType == ExcelFileType.xls)
                {
                    currentWorkbook = new HSSFWorkbook(file);
                }
                else if (currentExcelFileType == ExcelFileType.xlsx)
                {
                    currentWorkbook = new XSSFWorkbook(file);
                }
            }
        }
 public void resetCurrentDataTable()
        {
            currentTable = new DataTable();
        }
public void readExcelHeader(int sheetNum, int headerline, int contentline)
        {
            ISheet sheet = currentWorkbook.GetSheetAt(sheetNum);
            IRow row = sheet.GetRow(headerline);
            IRow contentRow = sheet.GetRow(contentline);
            

            for (int i = 0; i < row.LastCellNum; i++)
            {
                ICell cell = row.GetCell(i);
                ICell contentCell = contentRow.GetCell(i);

                // Handle incorrect format import if 1st content row has empty data.
                while (contentCell.IsCellEmpty())
                {
                    contentRow = sheet.GetRow(contentline++);
                    contentCell = contentRow.GetCell(i);
                }

                // Base on content value to decide Data coulumn type.
                if ((cell != null) && (contentCell != null))
                {
                    // ToDo: Refactor repeatable code.
                    if (contentCell.CellType == CellType.Numeric)
                    {
                        // Handle date time format.
                        if (HSSFDateUtil.IsCellDateFormatted(contentCell))
                            this.addImportTableColumn(cell.StringCellValue, TableColumnType.DateTime);
                        else
                            this.addImportTableColumn(cell.StringCellValue, TableColumnType.Decimal);
                    }
                    else if (contentCell.CellType == CellType.Formula)
                    {
                        switch (contentCell.CachedFormulaResultType)
                        {
                            case CellType.String:
                                this.addImportTableColumn(cell.StringCellValue, TableColumnType.String);
                                break;
                            case CellType.Numeric:
                                if (HSSFDateUtil.IsCellDateFormatted(contentCell))
                                    this.addImportTableColumn(cell.StringCellValue, TableColumnType.DateTime);
                                else
                                    this.addImportTableColumn(cell.StringCellValue, TableColumnType.Decimal);
                                break;
                        }
                    }
                    else if (contentCell.CellType == CellType.String)
                    {
                        this.addImportTableColumn(cell.StringCellValue, TableColumnType.String);
                    }
                    else
                    {
                        this.addImportTableColumn(cell.StringCellValue, TableColumnType.String);
                    }
                }
            }

        }
 public DataTable readExcelData(int sheetNum, int offsetLineNum)
        {
            ISheet sheet = currentWorkbook.GetSheetAt(sheetNum);
            int numOfRows = sheet.LastRowNum;

            for (int r = offsetLineNum; r < numOfRows - 1; r++)
            {
                IRow row = sheet.GetRow(r);
                DataRow dr = currentTable.NewRow();

                for (int i = 0; i < row.LastCellNum; i++)
                {
                    ICell cell = row.GetCell(i);
                    
                    if (cell == null)
                    {
                        dr[i] = null;
                        
                    }
                    else
                    {
                        if ((cell.CellType == CellType.Numeric) && (currentTable.Columns[i].DataType.IsNumericType()))
                        {
                            if (HSSFDateUtil.IsCellDateFormatted(cell))
                                dr[i] = cell.DateCellValue;
                            else
                                dr[i] = cell.NumericCellValue;
                        }
                        else if (cell.CellType == CellType.Formula)
                        {
                            switch (cell.CachedFormulaResultType)
                            {
                                case CellType.String:
                                    dr[i] = cell.StringCellValue;
                                    break;
                                case CellType.Numeric:
                                    if (HSSFDateUtil.IsCellDateFormatted(cell))
                                        dr[i] = cell.DateCellValue;
                                    else
                                        dr[i] = cell.NumericCellValue;
                                    break;
                            }
                        }
                        else if (cell.CellType == CellType.String)
                        {
                            dr[i] = cell.StringCellValue;
                        }
                        // Create default empty value.
                        else if (cell.IsCellEmpty())
                        {
                            dr[i] = Activator.CreateInstance(currentTable.Columns[i].DataType);
                        }
                        else
                        {
                            dr[i] = cell.ToString();
                        }
                    }
                }

                currentTable.Rows.Add(dr);
            }

            return currentTable;
        }
}

NPOI 是一套以POI 為基礎的Library, 它可以存取Word / Excel / PowerPoint / Outlook / Visio 及Publisher 檔案. 因為工作需要, 所以只研究了Excel 方面. 在示範中會讀取Excel 檔案並將內容顯示在DataGrid 內.

MainWindow.xaml

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:PoC.NPOI.Excel.VB"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Style TargetType="{x:Type Control}">
            <Setter Property="Margin" Value="10" />
        </Style>
        <Style TargetType="Button">
            <Setter Property="Width" Value="120" />
            <Setter Property="Margin" Value="10" />
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <StackPanel Grid.Row="0">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>
                <StackPanel Grid.Column="0">
                    <Button Width="100" Name="btnImport" Click="btnImport_Click">Import</Button>
                </StackPanel>
                <StackPanel Grid.Column="1" Orientation="Horizontal">
                    <TextBlock Text="Path: "/>
                    <TextBlock Name="txtPath" />
                </StackPanel>
            </Grid>
        </StackPanel>
        <DataGrid Grid.Row="1" Name="dgFileContent" HorizontalAlignment="Stretch" ItemsSource="{Binding }" />
    </Grid>
</Window>

MainWindow.xaml.vb

Imports System.Data
Imports System.IO
Imports Microsoft.Win32
Imports NPOI.HSSF.UserModel
Imports NPOI.SS.UserModel
Imports NPOI.XSSF.UserModel

Class MainWindow

    Public dataTable As DataTable

    Private Sub btnImport_Click(sender As Object, e As RoutedEventArgs)
        ' Create Dialog and get input file.
        Dim openFileDialog As OpenFileDialog = New OpenFileDialog() With
        {
            .Filter = "Excel 97-2000 Files (*.xls; *.xlsx)|*.xls; *.xlsx|Comma spearated Files (*.csv)|*.csv",
            .Multiselect = False
        }
        Dim openResult As Boolean?
        openResult = openFileDialog.ShowDialog(Me)

        ' Get file content and update datagrid.
        If (openResult.HasValue) And (openResult) Then
            ' Update text block.
            Me.txtPath.Text = openFileDialog.FileName

            Using fileStream As FileStream = openFileDialog.OpenFile()
                ' Open file and get first sheet.
                Dim excelWorkBook As IWorkbook
                Select Case Path.GetExtension(openFileDialog.FileName).ToUpper()
                    Case ".XLSX"
                        excelWorkBook = New XSSFWorkbook(fileStream)
                    Case Else
                        excelWorkBook = New HSSFWorkbook(fileStream)
                End Select

                Dim excelSheet As ISheet = excelWorkBook.GetSheetAt(0)

                If (excelSheet IsNot Nothing) Then
                    dataTable = New DataTable()
                    ' Create column for datatable.
                    Dim refRow As IRow = excelSheet.GetRow(0)
                    For c = refRow.FirstCellNum To refRow.LastCellNum - 1
                        Select Case refRow.GetCell(c).CellType
                            Case CellType.Numeric
                                dataTable.Columns.Add(New DataColumn("Header" & c, GetType(Decimal)))
                            Case CellType.String
                                dataTable.Columns.Add(New DataColumn("Header" & c, GetType(String)))
                            Case Else
                                dataTable.Columns.Add(New DataColumn("Header" & c, GetType(String)))
                        End Select
                    Next

                    ' Get each row and column data and add to DataGrid.
                    For r = 0 To excelSheet.LastRowNum - 1
                        Dim excelRow As IRow = excelSheet.GetRow(r)
                        Dim dataRow As DataRow = dataTable.NewRow()

                        For c = 0 To excelRow.LastCellNum - 1
                            dataRow(c) = excelRow.GetCell(c)
                        Next
                        dataTable.Rows.Add(dataRow)
                    Next
                    dgFileContent.DataContext = dataTable.DefaultView
                End If
            End Using
        End If
    End Sub
End Class