C# web三层架构 实现选择文件的导出路径并导出为excel

首先，你需要在前端页面上添加一个文件选择框，让用户选择要导出的文件。然后，将文件路径传递到后台，进行处理和导出。

在后台，你需要实现以下步骤：

1. 从前端获取文件路径

string filePath = Request.Form["filePath"];

2. 将数据导出为 Excel 文件

//创建Excel文件对象
ExcelPackage excel = new ExcelPackage();
//创建工作表
var sheet = excel.Workbook.Worksheets.Add("Sheet1");
//设置表头
sheet.Cells[1, 1].Value = "姓名";
sheet.Cells[1, 2].Value = "年龄";
//填充数据
sheet.Cells[2, 1].Value = "张三";
sheet.Cells[2, 2].Value = 18;
sheet.Cells[3, 1].Value = "李四";
sheet.Cells[3, 2].Value = 20;
//保存文件
string fileName = "export.xlsx";
string savePath = filePath + "\\" + fileName;
FileInfo file = new FileInfo(savePath);
excel.SaveAs(file);

3. 返回文件下载链接

Response.Clear();
Response.ContentType = "application/octet-stream";
Response.AppendHeader("Content-Disposition", "attachment;filename=" + fileName);
Response.TransmitFile(savePath);
Response.End();

完整的代码示例：

public ActionResult ExportExcel()
{
    string filePath = Request.Form["filePath"];
    if (string.IsNullOrEmpty(filePath))
    {
        return Content("请选择导出路径！");
    }

    //创建Excel文件对象
    ExcelPackage excel = new ExcelPackage();
    //创建工作表
    var sheet = excel.Workbook.Worksheets.Add("Sheet1");
    //设置表头
    sheet.Cells[1, 1].Value = "姓名";
    sheet.Cells[1, 2].Value = "年龄";
    //填充数据
    sheet.Cells[2, 1].Value = "张三";
    sheet.Cells[2, 2].Value = 18;
    sheet.Cells[3, 1].Value = "李四";
    sheet.Cells[3, 2].Value = 20;
    //保存文件
    string fileName = "export.xlsx";
    string savePath = filePath + "\\" + fileName;
    FileInfo file = new FileInfo(savePath);
    excel.SaveAs(file);

    //返回文件下载链接
    Response.Clear();
    Response.ContentType = "application/octet-stream";
    Response.AppendHeader("Content-Disposition", "attachment;filename=" + fileName);
    Response.TransmitFile(savePath);
    Response.End();

    return Content("导出成功！");
}