ASP.NET Cross session list - html

Question

I'm attempting to make a simple page that will compare multiple form submissions.
I have a html page with a form, and a for-loop that generates a div for each item in a list of form submissions. The list is passed from the controller. I am trying to maintain the list in the controller rather than rely on a database.
When I try to resubmit the form, which should add another object to the list, the list re initializes.
In debugging, I see that the list is empty when the form gets submitted. I'm unsure as to the correct terminology, but it seems that the list is emptied whenever the view is rendered. Is there a way to maintain list contents?
I know there are better ways to do this, and welcome any advice. I'm still learning, so pleas go easy.
Thanks!
This is the simplified controller.
namespace MvcApplication2.Controllers
{
public class HomeController : Controller
{
List<paymentPlan> plansList = new List<paymentPlan>();
public ActionResult Index()
{
return View(plansList);
}
[HttpPost]
public ActionResult Index(FormCollection collection)
{
paymentPlan Project = new paymentPlan();
Project.customerName = Convert.ToString(collection["customerName"]);
plansList.Add(Project);
return View(plansList);
}
}
}
This is my simplified view.
#model List<MvcApplication2.Models.paymentPlan>
#using (Html.BeginForm("index", "home", FormMethod.Post, new { Id = "signupForm" }))
{
<label for="customerName">Customer Name:</label>
<input type="text" name="customerName" class="form-control required" />
#Html.ValidationSummary(true)
<input type="submit" value="Calculate" class="btn btn-primary" />
}
#{
bool isEmpty = !Model.Any();
if (!isEmpty)
{
foreach (var i in Model)
{
<div>
Name: #i.customerName
</div>
}
}
}
This is my simplified model.
namespace MvcApplication2.Models
{
public class paymentPlan
{
public string customerName { get; set; }
}
}

Answer 1

I think that's a question of controller and asp.Net MVC lifecycle !
A controller lifetime is the same as the request, for each request a new controller is created and once the work is done it's disposed!
So try to remove this List<paymentPlan> plansList = new List<paymentPlan>(); and work with TempData[] or ViewData[] or Session[] like this :
Controller
public class HomeController : Controller
{
public ActionResult Index()
{
Session["plansList"] = ((List<paymentPlan>)Session["plansList"])!=null? (List<paymentPlan>)Session["plansList"] : new List<paymentPlan>();
return View((List<paymentPlan>)Session["plansList"]);
}
[HttpPost]
public ActionResult Index(FormCollection collection)
{
paymentPlan Project = new paymentPlan();
Project.customerName = Convert.ToString(collection["customerName"]);
((List<paymentPlan>)Session["plansList"]).Add(Project);
return View(plansList);
}
}
check this : http://www.asp.net/mvc/overview/getting-started/lifecycle-of-an-aspnet-mvc-5-application