asp.net MVC 2 Validating File uploads with data annotation

You can just use data annotations as per general usage.

For example, a viewmodel such as:

public class UpdateSomethingViewModel {
    [DisplayName("evidence")]
    [Required(ErrorMessage="You must provide evidence")]
    [RegularExpression(@"^abc123.jpg$", ErrorMessage="Stuff and nonsense")]
    public HttpPostedFileWrapper Evidence { get; set; }
}

Then in your controller just the usual:

[HttpPost]
public ActionResult UpdateSomething(UpdateHSomethingViewModel model)
{
    if (ModelState.IsValid)
    {
        // do stuff - plenty of stuff
        // weee, we're off to see the wizard.

        return RedirectToAction("UpdateSomethingSuccess", model);
    }

    return View(model);
}

I've just tested (albeit in MVC2/.net 4) and it worked a treat.

Hope that helps.

Cheers, Terry