How To: Provide Save File Dialog for an Image Request in ASP.Net

It is the default behavior of the web browsers, when you click on the image link, to open the image and display it over there. There are instances when you might want your users to remain on the page and simply download and save the image after clicking on the image link.

This functionality can be achieved in ASP.Net. Here I am going to show how to:

Create a blank ASP.Net Web Application. Now you have to create a folder to store the image to be downloaded and add and image to it.

Your solution should look similar to this:

Open the Default.aspx and create a HyperLink to the image like this:

<asp:HyperLink ID="hlDownloadImage" runat="server" NavigateUrl="~/Images/image001.jpg?Action=Download">Download Image</asp:HyperLink>

Note that the image URL is having additional parameter “Action” with value “Download”. We will see the utilization of the same in a moment.

now go and add a new file of Type ASP.Net Module ImageDownload.cs to the solution and modify the code as below:

public class ImageDownload : IHttpModule
{
    #region IHttpModule Members
    public void Dispose() { }

    public void Init(HttpApplication context)
    {
        context.BeginRequest += new EventHandler(context_BeginRequest);
    }
    #endregion

    public void context_BeginRequest(object sender, EventArgs e)
    {
        HttpApplication app = (HttpApplication)sender;
        HttpRequest req = app.Request;
        HttpResponse res = app.Response;
        if (req.Params["Action"] != null && req.Params["Action"].ToString() == "Download")
        {
            string path = req.AppRelativeCurrentExecutionFilePath;
            res.ContentType = "image/jpeg";
            res.AppendHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(path));
            res.TransmitFile(app.Server.MapPath(path));
            res.End();
        }
    }
}

Modify the web.config file to include following in <httpModules> section:

<add name="ImageDownload" type="WebUploadManager.ImageDownload"/>

You are done. Run the application and click on the Link for the image and you will see the Run/Save dialog. Try removing the Action parameter from the NavigationURL of the hyperlink; image will be displayed on screen as the default behavior of the browser.

Server.MapPath

In general whenever we need to get physical location of the file in ASP.Net Application, we use Server.MapPath. This is the most commonly adopted method. If you want the file to be located with reference to the path of the current WebPage, then the implementation holds good, but, in case you have to always refer the file from the application root, this method gives you different results. Take the following scenario, where the application directory structure is as follows:

  • Root
    • Data
      • Data.XML
    • ClassA.cs (uses Server.MapPath(“\Data\Data.XML”))
    • ClassB.cs (uses ClassA to get the XML file contents)
    • SubDir
      • ClassC.cs (uses ClassA to get the XML file contents)

In the above scenario the ClassC will fail to retrive the contents in case of the WebApplication is hosted in a virtual directory. The application will work fine if it is a website. So the implementation will not show any errors when we run the application from the Visual Studio. to make it more generic we can replace the Server.MapPath with

System.Web.Hosting.HostingEnvironment.ApplicationPhysicalPath + @”Data\Data.XML”.

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