c# winforms VS2017与excel链接：关闭表单时出错

Question

see image

这被认为是重复的帖子，因为确切的代码用于另一个问题（大约 5 年前。）。基本上，我收到错误 System.NullreferenceException: 'Object reference not set to an instance on an object '. 每次我关闭表单时，xlWorkBook.Close(true, misValue, misValue); 行（见图）。基于原来的问题：Inserting multiple textbox data into an Excel file，我找不到和我有同样问题的人。我使用的代码与链接相同：

`using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using Excel = Microsoft.Office.Interop.Excel;
 using System.Windows.Forms;

 namespace Vehicledettry
   {
     public partial class Form1 : Form
      {
    Microsoft.Office.Interop.Excel.Application xlexcel;
    Microsoft.Office.Interop.Excel.Workbook xlWorkBook;
    Microsoft.Office.Interop.Excel.Worksheet xlWorkSheet;
    object misValue = System.Reflection.Missing.Value;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        xlexcel = new Excel.Application();

        xlexcel.Visible = true;

        // Open a File
        xlWorkBook = xlexcel.Workbooks.Open(" C:\\vehicledet.xlsx", 0, true, 5, "", "", true,
        Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);

        xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);

        xlWorkSheet.Cells[1, 1] = "Plate Number";
        xlWorkSheet.Cells[1, 2] = "Car Model";
        xlWorkSheet.Cells[1, 3] = "Car Brand";
        xlWorkSheet.Cells[1, 4] = "Mileage";
    }

    private void button2_Click(object sender, EventArgs e)
    {
        int _lastRow = xlWorkSheet.Cells[xlWorkSheet.Rows.Count, 1].End[Excel.XlDirection.xlUp].Row + 1;

        xlWorkSheet.Cells[_lastRow, 1] = Plate Number.Text;
        xlWorkSheet.Cells[_lastRow, 2] = Car Model.Text;
        xlWorkSheet.Cells[_lastRow, 3] = Car Brand.Text;
        xlWorkSheet.Cells[_lastRow, 4] = Mileage.Text;

    }

    private void button3_Click(object sender, EventArgs e)
    {
        xlWorkBook.Close(true, misValue, misValue);
        xlexcel.Quit();

        releaseObject(xlWorkSheet);
        releaseObject(xlWorkBook);
        releaseObject(xlexcel);

    }

    private void releaseObject(object obj)
    {
        try
        {
            System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
            obj = null;
        }
        catch (Exception ex)
        {
            obj = null;
            MessageBox.Show("Unable to release the Object " + ex.ToString());
        }
        finally
        {
            GC.Collect();
        }
    }

}

我尝试在每个按钮事件单击后复制xlWorkBook = xlexcel.Workbooks.Open(" C:\\vehicledet.xlsx", 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);，但同样的错误不断发生。希望我能得到一些帮助。谢谢。

Answer 1

最近，我也有一个项目，它将数据发送到一个 excel 文件中，但与你的不同，我的数据来自一个文本文件，这个网站上的某个人帮助我弄清楚如何导出我的数组的值在 Excel 文件中。在您的情况下，此代码可能会有所帮助。

using Excel = Microsoft.Office.Interop.Excel;
Excel.Application exc = new Excel.Application();
exc.Interactive = true;
var excelTemplate = "CompareResult.xlsx"; //Change it with your filename
string FromPath = Path.GetFullPath(excelTemplate); //Get the full path of your excel 
//file.
Excel.Workbook wb = exc.Workbooks.Open(FromPath);
Excel.Worksheet sh = wb.Sheets[1];
int _lastRow = xlWorkSheet.Cells[xlWorkSheet.Rows.Count, 1].End[Excel.XlDirection.xlUp].Row + 1;
sh.Cells[row, 1].Value2 = textBox1.Text;
sh.Cells[row, 2].Value2 = textBox1.Text;
sh.Cells[row, 3].Value2 = textBox1.Text;
sh.Cells[row, 4].Value2 = textBox1.Text;
wb.Save(); \\Saving the file when changing
wb.Close(); 
exc.Quit();

Answer 2

（根据反馈编辑）见下文。文本框中的数据将自动进入现有的选择的 Excel 文件。非常感谢https://support.microsoft.com/en-in/help/302084/how-to-automate-microsoft-excel-from-microsoft-visual-c-net 的帮助

using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Excel = Microsoft.Office.Interop.Excel;
using System.Reflection;
using System.Windows.Forms;


namespace exceltry
  {
    public partial class Form1 : Form
     {
       public Form1()
        {
           InitializeComponent();
        }

private void button1_Click(object sender, System.EventArgs e)
  {
        Excel.Application xlexcel = null;
        Excel._Workbook xlWorkbook = null;
        Excel._Worksheet xlWorkSheet = null;
        Excel.Range oRng;

    try
       {
          //start excel and get application object
          oXL = new Microsoft.Office.Interop.Excel.Application();


          //open existing workbook
            oWB = oXL.Workbooks.Open("C:\\vehicledet.xlsx");
            oSheet = (Excel._Worksheet)oWB.ActiveSheet;

         //Add table headers going cell by cell.
          xlWorkSheet.Cells[1, 1] = "Plate Number";
          xlWorkSheet.Cells[1, 2] = "Car Model";
          xlWorkSheet.Cells[1, 3] = "Car Brand";
          xlWorkSheet.Cells[1, 4] = "Mileage";

         //Format A1:D1 as bold, vertical alignment = center.
          xlWorkSheet.get_Range("A1", "D1").Font.Bold = true;
          xlWorkSheet.get_Range("A1", "D1").VerticalAlignment = 
          Excel.XlVAlign.xlVAlignCenter;

          // insert text at every last row
            int _lastRow = xlWorkSheet.Range["A" +    xlWorkSheet.Rows.Count].End[Excel.XlDirection.xlUp].Row + 1;

            xlWorkSheet.Cells[_lastRow, 1] = textBox1.Text;
            xlWorkSheet.Cells[_lastRow, 2] = textBox2.Text;
            xlWorkSheet.Cells[_lastRow, 3] = textBox3.Text;
            xlWorkSheet.Cells[_lastRow, 4] = textBox4.Text;


            //AutoFit columns A:D.
            oRng = xlWorkSheet.get_Range("A1", "D1");
            oRng.EntireColumn.AutoFit();

            //Make sure Excel is not visible and give the user control of Microsoft Excel's lifetime.
            xlexcel.Visible = false;
            xlexcel.UserControl = true;

            //can save update to same file but wont close unless user press x button
            xlWorkbook.Save();
            MessageBox.Show("Data saved successfully");
            xlWorkbook.Close();

            //allow excel to auto close by itself 
            oXL.Quit();
            Marshal.ReleaseComObject(oXL);

        }
        catch (Exception theException)
        {
            String errorMessage;
            errorMessage = "Error: ";
            errorMessage = String.Concat(errorMessage, theException.Message);
            errorMessage = String.Concat(errorMessage, " Line: ");
            errorMessage = String.Concat(errorMessage, theException.Source);

            MessageBox.Show(errorMessage, "Error");
        }
    }
}