Model values not being preserved - asp.net-mvc-4

Question

I'm very new to ASP.NET MVC and I'm having trouble with something that seems like it should be a no-brainer.
With this ViewModel:
public enum Step
{
One = 1,
Two = 2,
Three = 3
}
public class TestViewModel
{
public string Description
{
get
{
return "Current step is " + this.Step;
}
}
public Step Step { get; set; }
public string Dummy{ get; set; }
public TestViewModel()
{ }
public TestViewModel(Step step)
{
this.Step = step;
}
}
and this view:
#using MvcApplication1
#model TestViewModel
#using (Html.BeginForm("Test", "Home"))
{
if (Model.Step == Step.One)
{
#Html.HiddenFor(m => m.Step)
#Html.HiddenFor(m => m.Dummy)
<p>#Model.Description</p>
}
else if (Model.Step == Step.Two)
{
#Html.HiddenFor(m => m.Step)
#Html.HiddenFor(m => m.Dummy)
<p>#Model.Description</p>
}
else if (Model.Step == Step.Three)
{
#Html.HiddenFor(m => m.Step)
#Html.HiddenFor(m => m.Dummy)
<p>#Model.Description</p>
}
<input type="submit" value="Continue" />
}
and this controller:
public ActionResult Test()
{
TestViewModel model = new TestViewModel(Step.One);
return View(model);
}
[HttpPost]
public ActionResult Test(TestViewModel model)
{
Debug.Print("Enter: Step = {0}", model.Step);
switch (model.Step)
{
case Step.One:
model.Step = Step.Two;
model.Dummy = "2";
break;
case Step.Two:
model.Step = Step.Three;
model.Dummy = "3";
break;
case Step.Three:
model.Step = Step.One;
model.Dummy = "1";
break;
}
Debug.Print("Enter: Step = {0}", model.Step);
return View(model);
}
On the first click of the button the controller sets model.Step to Step.Two and my view is updated correctly.
But on the second (and any subsequent) click of the button model.Step is read as Step.One instead of Step.Two so nothing is updated on my view.
Is there anything obvious that I'm missing here? Why are the values not being read/saved correctly?

Answer 1

You don't need if else blocks in your view. You are basically doing the same thing. This will also work:
#using (Html.BeginForm("Test", "Home"))
{
#Html.HiddenFor(m => m.Step)
<p>#Model.Description</p>
<input type="submit" value="Continue" />
}
After posting the form, you are returning a view in the same action. ASP.NET MVC only uses values from the POST request in HTML helpers, ignoring the updated values in your action. You can see it in HTML after you make the first request and here's the reason why it's implemented that way.
I would suggest implementing Post-Redirect-Get pattern. After updating the value, make a redirection to other action.
[HttpPost]
public ActionResult Test(TestViewModel model)
{
Debug.Print("Enter: Step = {0}", model.Step);
switch (model.Step)
{
case Step.One:
model.Step = Step.Two;
break;
case Step.Two:
model.Step = Step.Three;
break;
case Step.Three:
model.Step = Step.One;
break;
}
Debug.Print("Enter: Step = {0}", model.Step);
return RedirectToAction("SomeAction", model);
}
This will serialize the model into querystring. Better way would be to pass some ID as a parameter.