How to redirect to Details View? - asp.net-mvc-3

Question

This is my LearnController and here is the create.
[HttpPost]
public ActionResult Create(Learn learn)
{
if (ModelState.IsValid)
{
db.Learns.Add(learn);
db.SaveChanges();
return RedirectToAction("Details", new { id = learn.ModuleId });
}
ViewBag.ModuleId = new SelectList(db.Modules, "ModuleId", "Code", learn.ModuleId);
return View(learn);
}
Here is the detail in my LearnController
public ViewResult Details(int id)
{
var mod = db.Modules.Include("Learns").Single(g => g.ModuleId == id);
return View(mod);
}
In my create view of the learning controller, I place a HTMLActionLink but I can't seem to be redirected. Is there something wrong with my codes?
#Html.ActionLink("Back to List", "Details")
This is the error.
The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ViewResult Details(Int32)' in 'Module1.Controllers.LearnController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters

Answer 1

The link would need to be #Html.ActionLink("Back to List", "Details", new { id = # }) where # is the id of the Module to display. So when you create a new Learn the GET method would need to be something like
public ActionResult Create(int ID) // ID is the ModuleId your creating the Learn for
{
Learn model = new Learn();
model.ModuleID = ID;
return View(model);
}
and in the view
#model Learn
....
#Html.ActionLink("Back to List", "Details", new { id = Model.ModuleID })
This is assuming that the Details view contains a link to create a new Learn for the Module, where the link would be #Html.ActionLink("Add new Learn", "Create", new { id = Model.ID})
If you can create a new Learn from some other view (where you don't have access to the ID property of Module), and where the view to create a new Learn allows you to select the Module form a drop down list, then you would need javascript/jquery to update the href value of the link based on the selected Module

Answer 2

"The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32", the parameters should be nullable type, change to this
public ViewResult Details(int? id)
{
try
{
if (id.HasValue)
{
var mod = db.Modules.Include("Learns").Single(g => g.ModuleId == id);
if (mod == null)
throw new ArgumentException("Invalid ID");
return View(mod);
}
else
{
throw new ArgumentException("Invalid ID");
}
}
catch (ArgumentException ex)
{
return View(new Modules()); // assumed Details view model is Modules class
}
catch
{
return View(new Modules()); // assumed Details view model is Modules class
}
}
or
public ViewResult Details(string id)
{
try
{
int intId;
if(int.TryParse(id, out intId))
{
var mod = db.Modules.Include("Learns").Single(g => g.ModuleId == intId);
if (mod == null) throw new ArgumentException("Invalid ID");
return View(mod);
}
else
{
throw new ArgumentException("Invalid ID");
}
}
catch (ArgumentException ex)
{
return View(new Modules()); // assumed Details view model is Modules class
}
catch
{
return View(new Modules()); // assumed Details view model is Modules class
}
}
Update
I think I misunderstood your question, all you need to do is change
#Html.ActionLink("Back to List", "Details" })
to
#Html.ActionLink("Back to List", "Details", new { id = Model.ModuleId })
as suggested by Stephen Muecke