Multiple models in a view

I'd recommend using Html.RenderAction and PartialViewResults to accomplish this; it will allow you to display the same data, but each partial view would still have a single view model and removes the need for a BigViewModel

So your view contain something like the following:

@Html.RenderAction("Login")
@Html.RenderAction("Register")

Where Login & Register are both actions in your controller defined like the following:

public PartialViewResult Login( )
{
    return PartialView( "Login", new LoginViewModel() );
}

public PartialViewResult Register( )
{
    return PartialView( "Register", new RegisterViewModel() );
}

The Login & Register would then be user controls residing in either the current View folder, or in the Shared folder and would like something like this:

/Views/Shared/Login.cshtml: (or /Views/MyView/Login.cshtml)

@model LoginViewModel
@using (Html.BeginForm("Login", "Auth", FormMethod.Post))
{
    @Html.TextBoxFor(model => model.Email)
    @Html.PasswordFor(model => model.Password)
}

/Views/Shared/Register.cshtml: (or /Views/MyView/Register.cshtml)

@model ViewModel.RegisterViewModel
@using (Html.BeginForm("Login", "Auth", FormMethod.Post))
{
    @Html.TextBoxFor(model => model.Name)
    @Html.TextBoxFor(model => model.Email)
    @Html.PasswordFor(model => model.Password)
}

And there you have a single controller action, view and view file for each action with each totally distinct and not reliant upon one another for anything.

Another way is to use:

@model Tuple<LoginViewModel,RegisterViewModel>

I have explained how to use this method both in the view and controller for another example: Two models in one view in ASP MVC 3

In your case you could implement it using the following code:

In the view:

@using YourProjectNamespace.Models;
@model Tuple<LoginViewModel,RegisterViewModel>

@using (Html.BeginForm("Login1", "Auth", FormMethod.Post))
{
        @Html.TextBoxFor(tuple => tuple.Item2.Name, new {@Name="Name"})
        @Html.TextBoxFor(tuple => tuple.Item2.Email, new {@Name="Email"})
        @Html.PasswordFor(tuple => tuple.Item2.Password, new {@Name="Password"})
}

@using (Html.BeginForm("Login2", "Auth", FormMethod.Post))
{
        @Html.TextBoxFor(tuple => tuple.Item1.Email, new {@Name="Email"})
        @Html.PasswordFor(tuple => tuple.Item1.Password, new {@Name="Password"})
}

Note that I have manually changed the Name attributes for each property when building the form. This needs to be done, otherwise it wouldn't get properly mapped to the method's parameter of type model when values are sent to the associated method for processing. I would suggest using separate methods to process these forms separately, for this example I used Login1 and Login2 methods. Login1 method requires to have a parameter of type RegisterViewModel and Login2 requires a parameter of type LoginViewModel.

if an actionlink is required you can use:

@Html.ActionLink("Edit", "Edit", new { id=Model.Item1.Id })

in the controller's method for the view, a variable of type Tuple needs to be created and then passed to the view.

Example:

public ActionResult Details()
{
    var tuple = new Tuple<LoginViewModel, RegisterViewModel>(new LoginViewModel(),new RegisterViewModel());
    return View(tuple);
}

or you can fill the two instances of LoginViewModel and RegisterViewModel with values and then pass it to the view.

Use a view model that contains multiple view models:

   namespace MyProject.Web.ViewModels
   {
      public class UserViewModel
      {
          public UserDto User { get; set; }
          public ProductDto Product { get; set; }
          public AddressDto Address { get; set; }
      }
   }

In your view:

  @model MyProject.Web.ViewModels.UserViewModel

  @Html.LabelFor(model => model.User.UserName)
  @Html.LabelFor(model => model.Product.ProductName)
  @Html.LabelFor(model => model.Address.StreetName)

There are lots of ways...

1. with your BigViewModel you do:

   @model BigViewModel    
   @using(Html.BeginForm()) {
       @Html.EditorFor(o => o.LoginViewModel.Email)
       ...
   }
   

2. you can create 2 additional views

   Login.cshtml

   @model ViewModel.LoginViewModel
   @using (Html.BeginForm("Login", "Auth", FormMethod.Post))
   {
       @Html.TextBoxFor(model => model.Email)
       @Html.PasswordFor(model => model.Password)
   }
   

   and register.cshtml same thing

   after creation you have to render them in the main view and pass them the viewmodel/viewdata

   so it could be like this:

   @{Html.RenderPartial("login", ViewBag.Login);}
   @{Html.RenderPartial("register", ViewBag.Register);}
   

   or

   @{Html.RenderPartial("login", Model.LoginViewModel)}
   @{Html.RenderPartial("register", Model.RegisterViewModel)}
   

3. using ajax parts of your web-site become more independent

4. iframes, but probably this is not the case