Question

I have the below controller. I return the view if a error occurs but the form data is lost.
Would anyone have a idea how I could return the form data with the view?

[AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Register(FormCollection collection)
    {
        string usrname = collection["UserName"];
        string email = collection["Email"];
        string password = collection["Password"];
        string serial = collection["Serial"];
        ViewData["PasswordLength"] = MembershipService.MinPasswordLength;
        // In a real app, actually register the user now
        if (ValidateRegistration(usrname, email, password, password))
        {
            // Attempt to register the user
            MembershipCreateStatus createStatus = MembershipService.CreateUser(usrname, password, email, serial);

            if (createStatus == MembershipCreateStatus.Success)
            {
                //TODO userinformation

                datacontext.SaveChanges();
                FormsAuth.SignIn(collection["UserName"], false /* createPersistentCookie */);
                return RedirectToAction("Index", "Home");
            }
            else
            {
                ModelState.AddModelError("_FORM", ErrorCodeToString(createStatus));

                //I would like to return the view with the form data

                return View();
            }
        }

Answer 1

You should definitely use view models, strongly typed views and get rid of any FormCollection and magic strings, like this:

public class RegisterUserViewModel
{
    public string UserName { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }
    public string Serial { get; set; }
    public int PasswordLength { get; set; }
}

and then:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Register(RegisterUserViewModel model)
{
    model.PasswordLength = MembershipService.MinPasswordLength;
    // In a real app, actually register the user now
    if (ValidateRegistration(model.UserName, model.Email, model.Password, model.Password))
    {
        // Attempt to register the user
        MembershipCreateStatus createStatus = MembershipService.CreateUser(model.UserName, model.Password, model.Email, model.Serial);
        if (createStatus == MembershipCreateStatus.Success)
        {
            //TODO userinformation
            datacontext.SaveChanges();
            FormsAuth.SignIn(model.UserName, false /* createPersistentCookie */);
            return RedirectToAction("Index", "Home");
        }
        else
        {
            ModelState.AddModelError("_FORM", ErrorCodeToString(createStatus));
            return View(model);
        }
    }

    ...
}

The Visual Studio’s default ASP.NET MVC 3 application wizard creates an example of how to do this in the AccountController.