I'm just picking up .net MVC and I've come across something that I can't work out. I'm obviously missing some basic principle but would love some help.
I have a ViewModel with two IEnumerables that I want to use to create dropdownlistfors. My GET works fine, the lists are populated as expected.
Now I'm posting the ViewModel back to a POST method, not to do anything useful but just to try and understand how mvc works. I expected that I would simply be able to re-populate the dropdownlistfors from the model that was posted back - but I get a null reference exception.
Other values, such as partyid, in the ViewModel survive the POST so i'm confused.
I can get it to work if I repopulate the lists but that seems wrong.
Can someone give me a pointer?
My ViewModel
public class DemoViewModel
{
//properties
public IEnumerable<tbl_server_lookup> servers { get; set; }
public int serverId { get; set; }
public IEnumerable<tbl_site_lookup> sites { get; set; }
public int siteId { get; set; }
public int partyid { get; set; }
public string message { get; set; }
public DemoViewModel()
{
}
}
My Controller
// GET: /Demos/Test/
[HttpGet]
public ActionResult Test()
{
DemoViewModel demo = new DemoViewModel();
using (var dbContext = new ADAPI.Models.db_ad_apiEntities2())
{
var serverList = dbContext.tbl_server_lookup.Where(s => s.server_name != null);
demo.servers = serverList.ToList();
var siteList = dbContext.tbl_site_lookup.Where(w => w.site_name != null);
demo.sites = siteList.ToList();
}
demo.message = "Enter the user id you would like to look up in the box below.";
return View(demo);
}
//
//POST: /Demos/Test/
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Test(DemoViewModel demo)
{
//It works if I uncomment this block...
/*using (var dbContext = new ADAPI.Models.db_ad_apiEntities2())
{
var myQuery = dbContext.tbl_server_lookup.Where(s => s.server_name != null);
demo.servers = myQuery.ToList();
var siteList = dbContext.tbl_site_lookup.Where(w => w.site_name != null);
demo.sites = siteList.ToList();
}*/
demo.message = "the user id you posted is: " + demo.partyid + ". The Server you selected is: ";// +demo.serverId;
return View(demo);
}
My View
@model ADAPI.ViewModels.DemoViewModel
<h2>Demos</h2>
<h3>@Model.message</h3>
@using (Html.BeginForm("Test","Demos"))
{
@Html.AntiForgeryToken()
<div class="">
<h4>Party ID</h4>
@Html.ValidationSummary(true)
<!-- input box for party id-->
@Html.TextBoxFor(model => model.partyid)
<!-- dropdown list of server types eg live vs test-->
@Html.DropDownListFor(model => model.serverId, new SelectList(Model.servers, "server_Id","server_name"))
@Html.DropDownListFor(model => model.siteId, new SelectList(Model.sites, "site_short_name","site_name"))
<input type="submit" value="Try" />
</div>
}
The Error
