In versions of ASP.NET before 4.5 there was no direct way to enable a user to upload multiple files at once. The FileUpload control only supported a single file at the time. Common solutions to uploading multiple files were to use a server-side control such as those from Telerik or DevExpress or to use a client-side solution using a jQuery plugin for example. In the latter case, you would access Request.Files to get at the uploaded files, rather than retrieving them form a FileUpload control directly. Fortunately, in ASP.NET 4.5 uploading multiple files is now really easy.

The FileUpload Control with HTML5 Support

The FileUpload control has been enhanced in ASP.NET to support the HTML5 multiple attribute on an input with its type set to file. The server control has been expanded with an AllowMultiple attribute that renders the necessary HTML5 attribute. In addition, the control now has properties such as HasFiles and PostedFiles that enable you to work with a collection of uploaded files, rather than with just a single file as was the case with previous versions of the control.

All you need to do to enable multiple file uploads is set the AllowMultiple property of the FileUpload control to true:

<asp:FileUpload ID="FileUpload1" runat="server" AllowMultiple="true" />

In the browser, this renders the following HTML:

<input type="file" multiple="multiple" name="FileUpload1" id="FileUpload1" />

Notice how the multiple="multiple" attribute tells the browser to enable support for multiple files. Each browser that supports this feature uses a slight different interface. For example, in Chrome it looks like this:

while in Opera it looks like this:

All major browsers (Firefox, Chrome, Opera and Safari) except Internet Explorer 9 support this feature. IE 10 will support uploading multiple files as well, so hopefully this limitation is soon a thing of the past. While Safari seems to officially support this feature, I couldn't make the example work with multiple files. This could be a bug in Safari.

Working with the uploaded files at the server is similar to how you used to work with the control, except that you now work with a collection of files, rather than with a single instance. The following code snippet demonstrates how to save the uploaded files to disk and assign their names to a simple Label control, reporting back to the user which files were uploaded:

protected void Upload_Click(object sender, EventArgs e)
  if (FileUpload1.HasFiles)
    string rootPath = Server.MapPath("~/App_Data/");
    foreach (HttpPostedFile file in FileUpload1.PostedFiles)
      file.SaveAs(Path.Combine(rootPath, file.FileName));
      Label1.Text += String.Format("{0}<br />", file.FileName);

With this code, each uploaded file is saved in the App_Data folder in the root of the web site. Notice that this is just a simple example, and you would still need to write code you normally would to prevent existing files from being overwritten, and to block specific files types from being uploaded.