foreach on Request.Files

I'm attempting upload multiple files in ASP.NET MVC and I have this simple foreach loop in my controller

foreach (HttpPostedFileBase f in Request.Files)
{
    if (f.ContentLength > 0)
        FileUpload(f);
}

The previous code generates this error:

Unable to cast object of type 'System.String' to type 'System.Web.HttpPostedFile'. 

What I don't understand is why Request.Files[1] returns an HttpPostedFileBase but when it's iterated over, it returns strings (presumably the file names).

Note: I know this can be solved with a for loop. Also, I tried using HttpPostedFile, with the same error.

The enumerator on the HttpFileCollection returns the keys (names) of the files, not the HttpPostedFileBase objects. Once you get the key, use the Item ([]) property with the key (filename) to get the HttpPostedFileBase object.

foreach (string fileName in Request.Files)
{
    HttpPostedFileBase file = Request.Files[fileName];

    ...
}

With my tab HTML is:

<input class="valid" id="file" name="file" multiple="" type="file">

Request.Files will have duplicate name in array. So you should solve like this:

for (int i = 0; i < Request.Files.Count; i++ ){
    HttpPostedFileBase fileUpload = Request.Files[i];

We can use LINQ to do this and still use foreach as asked:

var files = Enumerable.Range(0, Request.Files.Count)
    .Select(i => Request.Files[i]);

foreach (var file in files)
{
    // file.FileName
}

As @tvanfosson said, the enumerator returns the file names as strings, not the HttpPostedFileBase. This method HttpPostedFileBase this[string name] returns the object we want. If HttpFileCollectionBase implemented IEnumerable<HttpPostedFileBase> then we could do the foreach normally. However, it implements a non-generic IEnumerable.