ASP.NET file download from server

Question

After a user clicks a button, I want a file to be downloaded. I've tried the following which seems to work, but not without throwing an exception (ThreadAbort) which is not acceptable.

    System.Web.HttpResponse response = System.Web.HttpContext.Current.Response;     response.ClearContent();     response.Clear();     response.ContentType = "text/plain";     response.AddHeader("Content-Disposition", "attachment; filename=" + fileName + ";");     response.TransmitFile(Server.MapPath("FileDownload.csv"));     response.Flush();     response.End();   

Answer 1

You can use an HTTP Handler (.ashx) to download a file, like this:

DownloadFile.ashx:

public class DownloadFile : IHttpHandler  {     public void ProcessRequest(HttpContext context)     {            System.Web.HttpResponse response = System.Web.HttpContext.Current.Response;         response.ClearContent();         response.Clear();         response.ContentType = "text/plain";         response.AddHeader("Content-Disposition",                             "attachment; filename=" + fileName + ";");         response.TransmitFile(Server.MapPath("FileDownload.csv"));         response.Flush();             response.End();     }      public bool IsReusable     {         get         {             return false;         }     } } 

Then you can call the HTTP Handler from the button click event handler, like this:

Markup:

<asp:Button ID="btnDownload" runat="server" Text="Download File"              OnClick="btnDownload_Click"/> 

Code-Behind:

protected void btnDownload_Click(object sender, EventArgs e) {     Response.Redirect("PathToHttpHandler/DownloadFile.ashx"); } 

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Passing a parameter to the HTTP Handler:

You can simply append a query string variable to the Response.Redirect(), like this:

Response.Redirect("PathToHttpHandler/DownloadFile.ashx?yourVariable=yourValue"); 

Then in the actual handler code you can use the Request object in the HttpContext to grab the query string variable value, like this:

System.Web.HttpRequest request = System.Web.HttpContext.Current.Request; string yourVariableValue = request.QueryString["yourVariable"];  // Use the yourVariableValue here 

Note - it is common to pass a filename as a query string parameter to suggest to the user what the file actually is, in which case they can override that name value with Save As...