C# WinForm导出Excel

概述

在.NET应用中，导出Excel是很常见的需求，在我维护的一个应用中就遇到到了这样的需求，需要每月定时从不同的Server的不同数据库中获取Excel报表，手动生成实在是非常蛋疼。导出Excel报表大致有以下三种方式：Office PIA，文件流和NPOI开源库，本文只介绍前两种方式。

Office PIA

.NET开发人员首选的方法，通过COM组件调用Office软件本身来实现文件的创建和读写，但是数据量较大的时候异常缓慢；如下代码所示已经做了优化，将一个二维对象数组赋值到一个单元格区域中（下面的代码中只能用于导出列数不多于26列的数据导出）：

public static void ExportToExcel(DataSet dataSet, string outputPath)
{
    Excel.ApplicationClass excel = new Excel.ApplicationClass();
    Excel.Workbook workbook = excel.Workbooks.Add(Type.Missing);
    int sheetIndex = 0;
    foreach (System.Data.DataTable dt in dataSet.Tables)
    {
        object[,] data = new object[dt.Rows.Count + 1, dt.Columns.Count];
        for (int j = 0; j < dt.Columns.Count; j++)
        {
            data[0, j] = dt.Columns[j].ColumnName;
        }
        for (int j = 0; j < dt.Columns.Count; j++)
        {
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                data[i + 1, j] = dt.Rows[i][j];
            }
        }
        string finalColLetter = string.Empty;

        string colCharset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        int colCharsetLen = colCharset.Length;
        if (dt.Columns.Count > colCharsetLen)
        {
            finalColLetter = colCharset.Substring(
                (dt.Columns.Count - 1) / colCharsetLen - 1, 1);
        }
        finalColLetter += colCharset.Substring(
                (dt.Columns.Count - 1) % colCharsetLen, 1);
        
        Excel.Worksheet sheet = (Excel.Worksheet)workbook.Sheets.Add(
            workbook.Sheets.get_Item(++sheetIndex),
            Type.Missing, 1, Excel.XlSheetType.xlWorksheet);
        sheet.Name = dt.TableName;
        string range = string.Format("A1:{0}{1}", finalColLetter, dt.Rows.Count + 1);
        sheet.get_Range(range, Type.Missing).Value2 = data;
        ((Excel.Range)sheet.Rows[1, Type.Missing]).Font.Bold = true;
    }
    workbook.SaveAs(outputPath, Excel.XlFileFormat.xlWorkbookNormal, Type.Missing,
        Type.Missing, Type.Missing, Type.Missing, Excel.XlSaveAsAccessMode.xlExclusive,
        Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
    workbook.Close(true, Type.Missing, Type.Missing);
    workbook = null;
    excel.Quit();
    KillSpecialExcel(excel);
    excel = null;
    GC.Collect();
    GC.WaitForPendingFinalizers();
}

[DllImport("user32.dll", SetLastError = true)]
static extern int GetWindowThreadProcessId(IntPtr hWnd, out int processId);

static void KillSpecialExcel(Excel.Application app)
{
    try
    {
        if (app != null)
        {
            int processId;
            GetWindowThreadProcessId(new IntPtr(app.Hwnd), out processId);
            System.Diagnostics.Process.GetProcessById(processId).Kill();
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

文件流

这种方法的效率明显高于第一种，而且也不需要安装Office，但是导出的xls文件并不符合Excel的格式标准，在打开生成的xls文件时会提示：The file you are trying to open is in a different format that specified by the file extension. Verify that the file is not corrupted and is from a trusted source before opening the file.

public static void ExportToExcel(System.Data.DataSet ds, string path)
{
    StreamWriter sw = null;
    try
    {
        long totalCount = ds.Tables[0].Rows.Count;
        sw = new StreamWriter(path, false, Encoding.Unicode);
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < ds.Tables[0].Columns.Count; i++)
        {
            sb.Append(ds.Tables[0].Columns[i].ColumnName + "\t");
        }
        sb.Append(Environment.NewLine);
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            for (int j = 0; j < ds.Tables[0].Columns.Count; j++)
            {
                sb.Append(ds.Tables[0].Rows[i][j].ToString() + "\t");
            }
            sb.Append(Environment.NewLine);
        }
        sw.Write(sb.ToString());
        sw.Flush();
    }
    catch (IOException ioe)
    {
        throw ioe;
    }
    finally
    {
        if (sw != null)
        {
            sw.Close();
        }
    }
}