将代码移动到类会导致HttpException错误

本文关键字：HttpException 错误 代码移动 | 更新日期: 2023-09-27 18:27:05

我已经编写了使用EPPlus将数据从网页导出到excel的代码，我想在整个项目中多次重用这些代码，所以我已经将代码移到了它自己的类中。

在页面上的代码中，它可以很好地工作，但当我将它移到自己的类中时，我在Response.Clear()行上得到以下错误：

System.Web.HttpException (0x80004005): Response is not available in this context

这是我的代码

ExcelHelper类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Data;
using OfficeOpenXml;
using OfficeOpenXml.Table;
namespace myClassLib
{
    public class ExcelHelper : System.Web.UI.Page
    {
        public void exportExcel(DataTable myDataTable)
        {
            Response.Clear();
            Response.Charset = "";
            Response.ContentEncoding = System.Text.Encoding.UTF8;
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
            Response.AddHeader("content-disposition", "attachment;filename=Output.xlsx");
            DataTable dt= myDataTable;
            ExcelPackage pck = new ExcelPackage();
            using(pck)
            {
                ExcelWorksheet wsDt = pck.Workbook.Worksheets.Add("Sheet1");
                wsDt.Cells["A1"].LoadFromDataTable(dt, true, TableStyles.None);
                int colNumber = 1;
                foreach (DataColumn col in dt.Columns) 
                {
                    if (col.DataType == typeof(DateTime))
                    {
                        wsDt.Column(colNumber).Style.Numberformat.Format = "yyyy-mm-dd";
                    }
                    colNumber = colNumber + 1;
                }
                wsDt.Cells[wsDt.Dimension.Address].AutoFitColumns();
                Response.BinaryWrite(pck.GetAsByteArray());
            }
            Response.Flush();
            Response.End();
        }
    }
}

调用类的代码

ExcelHelper myExcelHelper = new ExcelHelper();
myExcelHelper.exportExcel(myDataTable);

非常感谢您的任何帮助

将代码移动到类会导致HttpException错误

您从Page继承了帮助程序，可能是因为您希望访问Response属性中提供的HttpResponse实例。但是，Page类应该由ASP.NET http管道实例化，以便正确设置其所有内部状态。在你的场景中不会发生这种情况。如果您按照如下方式重构它，您可以在一个助手类中生成Excel，并将一些额外的好东西导出到文件中。

public class ExcelExporter 
{
    DataTable dt;
    string filename = "Output.xlsx";
    // create exporter for datatable
    public ExcelExporter(DataTable dt)
    {
        this.dt = dt;
    }
    // creates an exporter for a datatable and filename
    public ExcelExporter(DataTable dt, string filename):this(dt)
    {
        this.filename = filename;
    }
    // exports excel to given httpResponse
    public void Export(HttpResponse response)
    {
        Response.Clear();
        Response.Charset = "";
        Response.ContentEncoding = System.Text.Encoding.UTF8;
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
        Response.AddHeader(
            "content-disposition", 
            String.Format("attachment;filename={0}",filename));
        Response.BinaryWrite(Export());
        Response.Flush();
        Response.End();
    }
    // export excel package in path with defaukt name
    public void Export(string path)
    {
        Export(path, filename);
    }
    // export excel package as file in path
    public void Export(string path, string file)
    {
        var full = Path.Combine(path, file);
        File.WriteAllBytes(full, Export());
    }
    //exort Excel package as Byte array
    public byte[] Export()
    {
        ExcelPackage pck = new ExcelPackage();
        using (pck)
        {
            ExcelWorksheet wsDt = pck.Workbook.Worksheets.Add("Sheet1");
            wsDt.Cells["A1"].LoadFromDataTable(dt, true, TableStyles.None);
            int colNumber = 1;
            foreach (DataColumn col in dt.Columns)
            {
                if (col.DataType == typeof(DateTime))
                {
                    wsDt.Column(colNumber).Style.Numberformat.Format = "yyyy-mm-dd";
                }
                colNumber = colNumber + 1;
            }
            wsDt.Cells[wsDt.Dimension.Address].AutoFitColumns();
            return pck.GetAsByteArray();   
        }
    }
}

要使用这个新版本，您将在ASP.NET页面上如下调用它：

myExcelHelper = new ExcelExproter(myDataTable);
myExcelHelper.Export(Response); // Response will be the HttpResponse of the current executing page
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