1

使用 NPOI 并尝试在此处遵循教程： http ://www.zachhunter.com/2010/05/npoi-excel-template/ ，我遇到了“对象引用未设置为对象实例”错误在这一行：

sheet.GetRow(1).GetCell(1).SetCellValue("some test value")

尝试使用此代码时：

Imports System.IO
Imports System.Web.Security
Imports NPOI.HSSF.UserModel
Imports NPOI.SS.UserModel
Imports NPOI.SS.Util
Imports NPOI.HSSF.Util
Imports NPOI.POIFS.FileSystem
Imports NPOI.HPSF



Partial Public Class NPOI_01
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    End Sub

    Public Shared Sub ExportDataTableToExcel(ByVal memoryStream As MemoryStream, ByVal fileName As String)
        Dim response As HttpResponse = HttpContext.Current.Response
        response.ContentType = "application/vnd.ms-excel"
        response.AddHeader("Content-Disposition", String.Format("attachment;filename={0}", fileName))
        response.Clear()

        response.BinaryWrite(memoryStream.GetBuffer())
        response.[End]()
    End Sub

    Protected Sub DownloadReport_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim fs As New FileStream(Server.MapPath("spr_files\Book1.xls"), FileMode.Open, FileAccess.Read)

        Dim templateWorkbook As New HSSFWorkbook(fs, True)

        Dim sheet As HSSFSheet = templateWorkbook.GetSheet("Sheet1")

        sheet.GetRow(1).GetCell(1).SetCellValue("some test value")

        sheet.ForceFormulaRecalculation = True

        Dim ms As New MemoryStream()

        templateWorkbook.Write(ms)

        ExportDataTableToExcel(ms, "MyBook1Report.xls")
    End Sub


End Class

更新 我发现这种格式有效，如这篇博文所示 - http://www.leniel.net/2009/10/npoi-with-excel-table-and-dynamic-chart.html：

    Protected Sub DownloadReport_Click(ByVal sender As Object, ByVal e As EventArgs)
    Dim fs As New FileStream(Server.MapPath("spr_files\Book1.xls"), FileMode.Open, FileAccess.Read)

    Dim templateWorkbook As New HSSFWorkbook(fs, True)

    Dim sheet1 As HSSFSheet = templateWorkbook.GetSheet("Sheet1")
    Dim row1 As HSSFRow

    row1 = sheet1.CreateRow(1)
    row1.CreateCell(1).SetCellValue("some test value")
    'sheet1.GetRow(1).CreateCell(1).SetCellValue("some test value")

    sheet1.ForceFormulaRecalculation = True

    Dim ms As New MemoryStream()

    templateWorkbook.Write(ms)

    ExportDataTableToExcel(ms, "MyBook1Report.xls")
End Sub

然而问题仍然悬而未决……为什么第一个示例中的代码不起作用？您是否必须声明每一行新数据？当你有很多行数据库数据时会发生什么？

4

1 回答 1

3

在您的示例中，第一个用途sheet.GetRow(1)是抓取工作表中的现有行。第二个使用sheet1.CreateRow(1)，它在工作表中创建一个新行。从未使用/初始化过的行不存在，并且在使用创建它们之前无法访问CreateRow。

为了证明这一点，您可以制作一个有 1 行的工作表，并在一个单元格中输入一个值。您可以使用GetRow(1)抓取行，然后尝试GetRow(10)在不存在的行上使用。你会得到对象不存在，因为行还不能被创建。

于 2011-06-08T20:10:25.473 回答