在 ASP.NET 中处理文件下载答案

【问题标题】：Handling file download in ASP.NET在 ASP.NET 中处理文件下载
【发布时间】：2010-10-25 08:02:36
【问题描述】：

可以接受 C# 或 VB.NET 中的建议。

我有一个类来处理文件下载链接 ASP.NET 项目，如下所示：

Public Class AIUFileHandler    
    Public Shared Sub DownloadFileHandler(ByVal fileName As String, ByVal filePath As String)    
        Dim r As HttpResponse    
        r.ContentType = "application/vnd.openxmlformats-officedocument.presentationml.presentation"
        r.AddHeader("content-disposition", String.Format("attachment;filename={0}", fileName))
        r.TransmitFile(filePath)    
        r.[End]()    
    End Sub    
End Class

然后，我从 ASP.NET 页面后面的代码中调用该函数，如下所示：

Protected Sub btnGetForm_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnGetForm.Click
    Dim fileName = "test.docx"
    Dim filePath = Server.MapPath("~/pub/test.docx")  
    AIUFileHandler.DownloadFileHandler(fileName, filePath)
End Sub

我收到这样的错误消息：

对象引用未设置为对象的实例。

r.ContentType = "application/vnd.openxmlformats-officedocument.presentationml.presentation"

但是如果我这样使用它而不创建另一个类，它会起作用：

Protected Sub btnGetForm_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnGetForm.Click
    Dim fileName = "test.docx"
    Dim filePath = Server.MapPath("~/pub/test.docx")  
    Response.ContentType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
    Response.AddHeader("content-disposition", String.Format("attachment;filename={0}", fileName))
    Response.TransmitFile(filePath)
    Response.[End]()  
End Sub

我的班级有什么问题？

谢谢。

【问题讨论】：

标签： c# asp.net vb.net

【解决方案1】：

替换

Dim r As HttpResponse

与

Dim r as HttpResponse  = HttpContext.Current.Response

在AIUFileHandler 类中

【讨论】：

【解决方案2】：

在使用之前，您需要在DownloadFileHandler 方法中初始化r 变量：

Dim r As HttpResponse = HttpContext.Current.Response

或将其作为参数传递：

Public Class AIUFileHandler
    Public Shared Sub DownloadFileHandler(ByVal fileName As String, ByVal filePath As String, ByVal r as HttpResponse)
        r.ContentType = "application/vnd.openxmlformats-officedocument.presentationml.presentation"
        r.AddHeader("content-disposition", String.Format("attachment;filename={0}", fileName))
        r.TransmitFile(filePath)
        r.[End]()
    End Sub
End Class

并调用：

Protected Sub btnGetForm_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnGetForm.Click
    Dim fileName = "test.docx"
    Dim filePath = Server.MapPath("~/pub/test.docx")
    AIUFileHandler.DownloadFileHandler(fileName, filePath, Response)
End Sub

【讨论】：

【解决方案3】：

顺便说一句，我使用下一个代码将文件作为附件发送给用户：

var info = new FileInfo(Server.MapPath(path));
Response.Clear();
Response.AppendHeader("Content-Disposition", String.Concat("attachment; filename=", info.Name));
Response.AppendHeader("Content-Length", info.Length.ToString(CultureInfo.InvariantCulture));
Response.ContentType = type;
Response.WriteFile(info.FullName, true);
Response.End();

如果目标文件是以编程方式生成的，您也可以将其包装到 try-finally 块中：

var info = ..
try
{
    // do stuff
}
finally
{
    File.Delete(info.FullName);
}

【讨论】：