This is my DropdownList :

                        <div class="editor-label">
    <p>
        <%: Html.LabelFor(model => model.Gov) %>
    </p>
    </div>
    <div class="editor-field">
    <p>
        <%=Html.DropDownListFor(model => model.Gov, ViewBag.gov as SelectList)%>
        <%: Html.ValidationMessageFor(model => model.Gov) %>
    </p>

and this is my view controller :

        public ActionResult TestR()
    {
        ViewBag.gov = new SelectList(entity.gouvernerat, "Idgov", "Nomg");
        return View();
    }

With HttpPost :

 [HttpPost]
    public ActionResult TestR(LogModel.preRegister Model)
    {
        if (ModelState.IsValid)
        {
            if (LogModel.preRegister.Verifuser(Model.IDag))
            {
                ModelState.AddModelError("", "Agence existe deja");
                return View(Model);
            }
            else
            {
                int ins = LogModel.preRegister.Register(Model);
                if (ins > 0)
                {

                    return View("Index");
                }
                else return View();
            }
        }
        else
        {
            return View();
        }

    }

Now Dropdown list show me the list of Gov in my DB(that's what i want), but when i clic on create i got this error in my DropdownLisrt There is no ViewData item of type 'IEnumerable <SelectListItem>' with key 'Gov'.

• asp.net-mvc
• ado.net

This is pretty easy with LINQ to SQL. Let's say you have a table Govs that contains your "Tunis", "Ariana", etc. strings. You can then create your select list like this:

govs.Select( x => new SelectListItem { Text = x.Name, Value = x.Name } );

Of course you can even be more flexible and assign the value to something else, like an ID.

Update: more details to answer questions posed in comments:

Add the select list items in the view model:

public IEnumerable<SelectListItem> GovItems { get; set; }

Then, in the controller, before returning your view:

// database code to get "Govs" table goes here....

var vm = new MyViewModel {
  GovItems = govs.Select( x => new SelectListItem { Text = x.Name, Value = x.Name } );
}

Then in your view:

@Html.DropDownListFor( x => x.Gov, Model.Govs )

I hope this helps. If you're still confused, I recommend reading some tutorials about ASP.NET MVC. I recommend Microsoft's official one:

http://www.asp.net/mvc/tutorials/getting-started-with-aspnet-mvc3/getting-started-with-mvc3-part1-cs