1.引入EPPlus.dll,舊版的是OfficeOpenXml.dll，最好使用EPPlus
2.調用 string path = UploadExecl(batchUpload.BinaryExcel, "xlsx");，獲取上傳的xlsx路徑
3. 下載Execl
3.1 如果是<a> 標簽的連接，可以將方法直接寫在 href上就能直接下載
<a href="/FangAn/DetailAuditOutPut/" target="_blank" style="color:#fff;"><el-button type="primary">導出Execl</el-button></a>
後臺方法調用：
byte[] result = GetExcelByte(model);
返回值為 File();
return File(result, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", model.OrderName + ".xlsx");

3.2 如果是js異步操作,需要下載的話：
後臺方法調用：
byte[] result = GetExcelByte(dt, modelReturn.errMessage);
string basestr = Convert.ToBase64String(result);
返回值為base64的字符串
return basestr;
而前臺，在需要多加一步操作，可以直接下載：
//res.data 為異步返回值，就是basestr
window.location.href = "data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64," + res.data;

/// <summary>
/// datatable導出
/// </summary>
/// <param name="dt"></param>
/// <returns></returns>
public byte[] GetExcelByte(DataTable dt, string err)
{
using (ExcelPackage package = new ExcelPackage())
{
ExcelWorksheet workSheet = package.Workbook.Worksheets.Add("候車亭批量導入");
workSheet.Cells[1, 1].Value = "媒體類型*";
workSheet.Cells[1, 2].Value = "類型子類*";
workSheet.Cells[1, 3].Value = "媒體位置*";
for (int i = 1; i < dt.Rows.Count; i++)
{
DataRow dr = dt.Rows[i];
workSheet.Cells[i + 1, 1].Value = dr[0];
workSheet.Cells[i + 1, 2].Value = dr[1];
workSheet.Cells[i + 1, 3].Value = dr[2];
}
return package.GetAsByteArray();
}
}

/// <summary>
/// execl轉成table
/// </summary>
/// <param name="path"></param>
/// <returns></returns>
public DataTable ExcelToTable(string path)
{
DataTable vTable = new DataTable();
FileInfo existingFile = new FileInfo(path);
try
{
FileInfo file = new FileInfo(path);
using (ExcelPackage package = new ExcelPackage(file))
{
ExcelWorksheet worksheet = package.Workbook.Worksheets[1];
int vSheetCount = package.Workbook.Worksheets.Count;
//獲取總Sheet頁
int maxColumnNum = worksheet.Dimension.End.Column;//最大列
int minColumnNum = worksheet.Dimension.Start.Column;//最小列
int maxRowNum = worksheet.Dimension.End.Row;//最小行
int minRowNum = worksheet.Dimension.Start.Row;//最大行

DataColumn vC;
for (int j = 1; j <= maxColumnNum; j++)
{
vC = new DataColumn("A_" + j, typeof(string));
vTable.Columns.Add(vC);
}
for (int n = 1; n <= maxRowNum; n++)
{
DataRow vRow = vTable.NewRow();
for (int m = 1; m <= maxColumnNum; m++)
{
vRow[m - 1] = worksheet.Cells[n, m].Value;
}
vTable.Rows.Add(vRow);
}
}

}
catch (Exception vErr)
{
Console.WriteLine(vErr.Message);
}
return vTable;
}
/// <summary>
/// 把二進制流轉成文件
/// </summary>
/// <param name="path">二進制流，類似(data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,)開頭的字符串</param>
/// <param name="path">文件擴展名</param>
/// <returns></returns>
public string UploadExecl(string path, string extension)
{
string sPath = host.ContentRootPath + "\\BatchUpload";//保存的路徑
if (!Directory.Exists(sPath))
{
Directory.CreateDirectory(sPath);
}
var regex = new Regex(@"data:(?<mime>[\w/\-\.]+);(?<encoding>\w+),(?<data>.*)", RegexOptions.Compiled);
var match = regex.Match(path);

var mimeType = match.Groups["mime"].Value;
var encodingCode = match.Groups["encoding"].Value;
var data = match.Groups["data"].Value;
byte[] targetFileByte = Convert.FromBase64String(data);

string[] mimeExtension = mimeType.Split(‘/‘);
string fileExtension = extension;
Random random = new Random();
//文件保存
string fileName = string.Format("{0:yyyyMMddHHmmss}{1}", DateTime.Now, random.Next());
string filePath = string.Format("{0}\\{1}.{2}", sPath, fileName, fileExtension);
FileStream file = new FileStream(filePath, FileMode.CreateNew, FileAccess.Write);
file.Write(targetFileByte,0, targetFileByte.Length);
file.Close();

return filePath;
}

ExcelPackage導入導出,命名空間一定要是EPPlus