Question

I’m new to MVC 3 / Razor and working on a simple site to learn the basics. To that end, I’ve created a simple view that renders a DropDownList on a page at /Home/SignedInAs.

The logic in my Home Controller is:

public class HomeController : Controller  
{  
  public ActionResult SignedInAs()  
  {  
    SignedInAsViewModel siavm = new SignedInAsViewModel();  
    siavm.SignedInAsOptions = db.GetSignedInAsOptions();  
    return View(siavm);
  }  
}  

where SignedInAsViewModel is a simple:

public class SignedInAsViewModel  
{  
  public SignedInAsViewModel()  
  {  
    this.SignedInAsOptions = new List<SignedInAs>();  
  }  

  public IEnumerable<SignedInAs> SignedInAsOptions { get; set; }  
}

and the method, db.GetSignedInAsOptions() returns a List of SignedInAs objects with the properties, ID and Name.

And in Views/Home/SignedInAs.cshtml, I have:

@model myMVCApp.Views.SignedInAsViewModel  
...  
@Html.DropDownList("ddlSignedInAs", new SelectList(Model.SignedInAsOptions, "ID", "Name", selectedValue))
...

And the Select list renders exactly as expected on my page at /Home/SignedInAs.

What I really want to do is render the DropDownList at the top of every page. So, I created a partial view, _SignedInAsPartial:

@model myMVCApp.Views.SignedInAsViewModel
@if (Request.IsAuthenticated)
{   
  <text><div>@Html.DropDownList("ddlSignedInAs", new SelectList(Model.SignedInAsOptions, "ID", "Name", selectedValue))</div></text>
}  

And a controller, SignedInAsController:

public class SignedInAsController : Controller
{
  public ActionResult ShowSignedInAs()
  {
    SignedInAsViewModel siavm = new SignedInAsViewModel();
    siavm.SignedInAsOptions = GetSignedInAsOptions();
    return PartialView(siavm);
  }
}  

(I have tried return View(siavm) here as well.)

And in my _Layout.cshtml used by all pages I have:

@Html.Partial("_SignedInAsPartial")  

Trying to load any page now results in a NullReferenceException and the visual debugger stops at _SignedInAsPartial.cshtml

Breakpoints never get hit in the SignedInAsController.

I obviously don’t understand something here, and I’ve read everything I can find. But I can’t figure it out. Why does the select list render fine on a page view, but not on a partial view?

Answer 1

You have to either pass the model to the partial view or you can use Html.RenderAction, which would require a controller action to back that view.