Asp.Net MVC DropDownListFor : how can the value be the whole object

Question

I need on one view to only choose between several element in a list. Element of my list are complex type.

I receive in the viewBag the list of all elements I can choose.

I tried several things without success, the most approaching thing of what I want is this:

@{SelectList list = new SelectList(ViewBag.Entities, Model);}
@Html.DropDownListFor(x => x, list);

Have you an idea about how to use this?

EDIT: Tried this too:

@Html.DropDownListFor(x => x, new SelectList(ViewBag.Entities, "", "Name"));

EDIT2: also tried to change my model, having a "int" as id, representing the current id of entity

@Html.DropDownListFor(x => x, new SelectList(ViewBag.Entities, "Id", "Name"));

Still have this exception:

System.ArgumentException was unhandled by user code
  Message=Value cannot be null or empty.
Parameter name: name
  Source=System.Web.Mvc
  ParamName=name
  StackTrace:
       at System.Web.Mvc.Html.SelectExtensions.SelectInternal(HtmlHelper htmlHelper, String optionLabel, String name, IEnumerable`1 selectList, Boolean allowMultiple, IDictionary`2 htmlAttributes)
       at System.Web.Mvc.Html.SelectExtensions.DropDownListFor[TModel,TProperty](HtmlHelper`1 htmlHelper, Expression`1 expression, IEnumerable`1 selectList, String optionLabel, IDictionary`2 htmlAttributes)
       at System.Web.Mvc.Html.SelectExtensions.DropDownListFor[TModel,TProperty](HtmlHelper`1 htmlHelper, Expression`1 expression, IEnumerable`1 selectList)
       at ASP._Page_Areas_Account_Views_Auth_EntityChooser_cshtml.Execute() in d:\Workspace\XYZ\Main\Code\AdManager\Areas\Account\Views\Auth\EntityChooser.cshtml:line 20
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
       at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
       at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
       at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
       at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
       at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19()
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
  InnerException: 

Answer 1

Solution I finally found a way to do it:

@Html.DropDownListFor(x => x.SelectedId, new SelectList(
    Model.AvailableEntities, "Id", "Name"));

I had to put a property on my model which can store the value. It seems that the DropDownListFor doesn't really likes that I've this x=>x

Answer 2

The method you're calling, defines Model as the SelectedValue. You should give the names to use for dataValueField and dataTextField:

@{SelectList list = new SelectList(ViewBag.Entities, "Key", "Value");}
@Html.DropDownListFor(x => x, list);

Given that ViewBag.Entities is a Dictionary. If it contains a list of your own objects, simply point to the properties you want to use, instead of Key and Value.